VUDEEVUDEE'S GEOGRAPHY BLOG

THE UNDERLYING THEORIES AND MODELS OF POPULATION

noreply@blogger.com (Unknown) — Wed, 29 Feb 2012 13:47:00 +0000

1. Malthusian Population Theories

Malthus argued that "Population grow at a rate that exceeds available food supply"
Population can survive only because of positive checks on population growth. That is, in mortality due to famines, epidemics, wars and natural causes, preventive checks e.g. abstinence and contraception.

2. Neo-Malthusian

Contemporary follower of the Malthus ideas
They focus more on the health and mortality consequences of a changing environment e.g. Each argue that the impact on the environment is a function of population size, level of affluence and technology.

3. Marxist Theories

In Marx's view, population growth is closely linked to the mode of production and level of development.
He argued that there are too many poor people due to capitalist exploitation.
Proper economic and social arrangements could accommodate population growth.

4. Demographic Transition Theory

Follow demographic theory of Europe.
When the population has a high rate and high death rate that population will not grow. That is, population growth is equal to zero.

This theory has four stages

Stage I : Low Growth

-If the population has a very high and varied birth and death rates due to poverty and poor sanitation, there will be virtually low population growth.

-Most of human history was spent in stage I.

-Currently there is no stage I country today.

Stage II : High Growth

-In this stage, Death rate drops due to: Improved sanitation and food nutrients.

-Countries in Europe and North America entered stage II in the late 18^th-19^thcentury.

Stage III : Moderate Growth

-Birth rate begins to drop sharply due to industrialization and changing attitudes towards ideal family size.

-Death rate continues to fall but at a much lower rate than in stage II.

-Population continue to grow at a more moderate rate.

-Countries in Europe and North America entered this Stage during the first half of the 20^th century. Some countries in Asia, Africa and Latin America entered Stage III recently.

Stage IV : Low Growth

-Birth rate decline to the point where it almost equals to the death rate.

-Natural growth rate approaches to zero.

-Sweden, Denmark, Germany, U.K have entered stage IV

STRENGTH OF DEMOGRAPHIC TRANSITION THEORY

Strongly descriptively.
It provides trends in birth and death rate in western countries during the Industrial Revolution.
Demographic transition, as a framework is useful for classifying population. Example, developing nations belong in stage I or II while developed nations fit in stage III or IV.
Demographic transition has predict population growth.

WEAKNESS OF DEMOGRAPHIC TRANSITION THEORY

Poor explanation of population change, it does not specify mechanism of such change.
Progress through demographic transition is not automatic.
It fails to account for any reversal that might occur in the process.
It is silent on the role of migration.

5. Epidemiological Transition Theory

Explains pattern of health and disease and its influence to mortality.
Base on patterns experienced in developed countries.

Has four stages

Predominant of famine and pestilence
Decline of infectious diseases.
Rise of degenerative diseases.
Rise of "hubristic" behavior (smoking, unprotected sex)

GEOGRAPHIC INFORMATION SYSTEM

noreply@blogger.com (Unknown) — Mon, 30 Jan 2012 18:15:00 +0000

The advent of cheap and powerful computers over the last few decades has allowed for the development of innovative software applications for the storage, analysis, and display of geographic data. Many of these applications belong to a group of software known as Geographic Information Systems (GIS). Many definitions have been proposed for what constitutes a GIS. Each of these definitions conforms to the particular task that is being performed. Instead of repeating each of these definitions, I would like to broadly define GIS according to what it does. Thus, the activities normally carried out on a GIS include:

The measurement of natural and human made phenomena and processes from a spatial perspective. These measurements emphasize three types of properties commonly associated with these types of systems: elements, attributes, and relationships.
The storage of measurements in digital form in a computer database. These measurements are often linked to features on a digital map. The features can be of three types: points, lines, or areas (polygons).
The analysis of collected measurements to produce more data and to discover new relationships by numerically manipulating and modeling different pieces of data.
The depiction of the measured or analyzed data in some type of display - maps, graphs, lists, or summary statistics.

The first computerized GIS began its life in 1964 as a project of the Rehabilitation and Development Agency Program within the government of Canada. The Canada Geographic Information System (CGIS) was designed to analyze Canada's national land inventory data to aid in the development of land for agriculture. The CGIS project was completed in 1971 and the software is still in use today. The CGIS project also involved a number of key innovations that have found their way into the feature set of many subsequent software developments.

From the mid-1960s to 1970s, developments in GIS were mainly occurring at government agencies and at universities. In 1964, Howard Fisher established the Harvard Lab for Computer Graphics where many of the industries early leaders studied. The Harvard Lab produced a number of mainframe GIS applications including: SYMAP (Synagraphic Mapping System),CALFORM, SYMVU, GRID, POLYVRT, and ODYSSEY. ODYSSEY was first modern vector GIS and many of its features would form the basis for future commercial applications. Automatic Mapping System was developed by the United States Central Intelligence Agency (CIA) in the late 1960s.

This project then spawned the CIA's World Data Bank, a collection of coastlines, rivers, and political boundaries, and the CAM software package that created maps at different scales from this data. This development was one of the first systematic map databases. In 1969, Jack Dangermond, who studied at the Harvard Lab for Computer Graphics, co-founded Environmental Systems Research Institute (ESRI) with his wife Laura. ESRI would become in a few years the dominate force in the GIS marketplace and create ArcInfo and ArcView software. The first conference dealing with GIS took place in 1970 and was organized by Roger Tomlinson (key individual in the development of CGIS) and Duane Marble (professor at Northwestern University and early GIS innovator). Today, numerous conferences dealing with GIS run every year attracting thousands of attendants.

In the 1980s and 1990s, many GIS applications underwent substantial evolution in terms of features and analysis power. Many of these packages were being refined by private companies who could see the future commercial potential of this software. Some of the popular commercial applications launched during this period include: ArcInfo, ArcView, MapInfo, SPANS GIS, PAMAP GIS, INTERGRAPH, and SMALLWORLD. It was also during this period that many GIS applications moved from expensive minicomputer workstations to personal computer hardware.

Components of a GIS

A Geographic Information System combines computer cartography with a database management system. Figure 1 describes some of the major components common to a GIS. This diagram suggests that a GIS consists of three subsystems: (1) an input system that allows for the collection of data to be used and analyzed for some purpose; (2) computer hardware and software systems that store the data, allow for data management and analysis, and can be used to display data manipulations on a computer monitor; (3) an output system that generates hard copy maps, images, and other types of output.

Figure 1: Three major components of a Geographic Information System. These components consist of input, computer hardware and software, and output subsystems.

Two basic types of data are normally entered into a GIS. The first type of data consists of real world phenomena and features that have some kind of spatial dimension. Usually, these data elements are depicted mathematically in the GIS as either points, lines, or polygons that are referenced geographically (or geocoded) to some type of coordinate system. This type data is entered into the GIS by devices like scanners, digitizers, GPS, air photos, and satellite imagery. The other type of data is sometimes referred to as an attribute. Attributes are pieces of data that are connected or related to the points, lines, or polygons mapped in the GIS. This attribute data can be analyzed to determine patterns of importance. Attribute data is entered directly into a database where it is associated with element data.

The difference between element and attribute data can be illustrated in Figures 2 and 3. Figure 2 shows the location of some of the earthquakes that have occurred in the last century. These plotted data points can be defined as elements because their main purpose is to describe the location of the earthquakes. For each of the earthquakes plotted on this map, the GIS also has data on their depth. These measurements can be defined as attribute data because they are connected to the plotted earthquake locations in Figure 2. Figure 3 shows the attribute earthquake depth organized into three categories: shallow; intermediate; and deep. This analysis indicates a possible relationship between earthquake depth and spatial location - deep earthquakes do not occur at the mid-oceanic ridges.

Figure 2: Distribution of earthquake events that have occurred over the last century.

Figure 3: Earthquake events organized according to depth (yellow (shallow) = surface to 25 kilometers below the surface, red (intermediate) = 26 to 75 kilometers below the surface, and black (deep) = 76 to 660 kilometers below the surface).

Within the GIS database a user can enter, analyze, and manipulate data that is associated with some spatial element in the real world. The cartographic software of the GIS enables one to display the geographic information at any scale or projection and as a variety of layers which can be turned on or off. Each layer would show some different aspect of a place on the Earth. These layers could show things like a road network, topography, vegetation cover, streams and water bodies, or the distribution of annual precipitation received. The output illustrated in Figure 4 merges data layers for vegetation community type, glaciers and ice fields, and water bodies (streams, lakes, and ocean).

Figure 4: Graphic output from a GIS. This GIS contains information about the major plant communities, lakes and streams, and glaciers and ice fields found occupying the province of British Columbia, Canada. The output shows Vancouver Island and part of the British Columbia mainland.

CITATION: Pidwirny, M. (2006). "Introduction to Geographic Information Systems". Fundamentals of Physical Geography, 2nd Edition. 30/1/2012.

REMOTE SENSING

noreply@blogger.com (Unknown) — Mon, 30 Jan 2012 17:55:00 +0000

Remote sensing can be defined as the collection of data about an object from a distance. Humans and many other types of animals accomplish this task with aid of eyes or by the sense of smell or hearing. Geographers use the technique of remote sensing to monitor or measure phenomena found in the Earth's lithosphere, biosphere, hydrosphere, and atmosphere. Remote sensing of the environment by geographers is usually done with the help of mechanical devices known as remote sensors. These gadgets have a greatly improved ability to receive and record information about an object without any physical contact. Often, these sensors are positioned away from the object of interest by using helicopters, planes, and satellites. Most sensing devices record information about an object by measuring an object's transmission of electromagnetic energy from reflecting and radiating surfaces.

Remote sensing imagery has many applications in mapping land-use and cover, agriculture, soils mapping, forestry, city planning, archaeological investigations, military observation, and geomorphological surveying, among other uses. For example, foresters use aerial photographs for preparing forest cover maps, locating possible access roads, and measuring quantities of trees harvested. Specialized photography using color infrared film has also been used to detect disease and insect damage in forest trees.

The simplest form of remote sensing uses photographic cameras to record information from visible or near infrared wavelengths (Table 1). In the late 1800s, cameras were positioned above the Earth's surface in balloons or kites to take oblique aerial photographs of the landscape. During World War I, aerial photography played an important role in gathering information about the position and movements of enemy troops. These photographs were often taken from airplanes. After the war, civilian use of aerial photography from airplanes began with the systematic vertical imaging of large areas of Canada, the United States, and Europe. Many of these images were used to construct topographic and other types of reference maps of the natural and human-made features found on the Earth's surface.

Table 1: Major regions of the electromagnetic spectrum.

Region Name	Wavelength	Comments
Gamma Ray	< 0.03 nanometers	Entirely absorbed by the Earth's atmosphere and not available for remote sensing.
X-ray	0.03 to 30 nanometers	Entirely absorbed by the Earth's atmosphere and not available for remote sensing.
Ultraviolet	0.03 to 0.4 micrometers	Wavelengths from 0.03 to 0.3 micrometers absorbed by ozone in the Earth's atmosphere.
Photographic Ultraviolet	0.3 to 0.4 micrometers	Available for remote sensing the Earth. Can be imaged with photographic film.
Visible	0.4 to 0.7 micrometers	Available for remote sensing the Earth. Can be imaged with photographic film.
Infrared	0.7 to 100 micrometers	Available for remote sensing the Earth. Can be imaged with photographic film.
Reflected Infrared	0.7 to 3.0 micrometers	Available for remote sensing the Earth. Near Infrared 0.7 to 0.9 micrometers. Can be imaged with photographic film.
Thermal Infrared	3.0 to 14 micrometers	Available for remote sensing the Earth. This wavelength cannot be captured with photographic film. Instead, mechanical sensors are used to image this wavelength band.
Microwave or Radar	0.1 to 100 centimeters	Longer wavelengths of this band can pass through clouds, fog, and rain. Images using this band can be made with sensors that actively emit microwaves.
Radio	> 100 centimeters	Not normally used for remote sensing the Earth.

The development of color photography following World War II gave a more natural depiction of surface objects. Color aerial photography also greatly increased the amount of information gathered from an object. The human eye can differentiate many more shades of color than tones of gray (Figure 1 and 2). In 1942, Kodak developed color infrared film, which recorded wavelengths in the near-infrared part of the electromagnetic spectrum. This film type had good haze penetration and the ability to determine the type and health of vegetation.

Figure 1: The rows of color tiles are replicated in the right as complementary gray tones. On the left, we can make out 18 to 20 different shades of color. On the right, only 7 shades of gray can be distinguished.

Figure 2: Comparison of black and white and color images of the same scene. Note how the increased number of tones found on the color image make the scene much easier to interpret. (Source: University of California at Berkley - Earth Sciences and Map Library).

Satellite Remote Sensing

In the 1960s, a revolution in remote sensing technology began with the deployment of space satellites. From their high vantage-point, satellites have a greatly extended view of the Earth's surface. The first meteorological satellite, TIROS-1 (Figure 3), was launched by the United States using an Atlas rocket on April 1, 1960. This early weather satellite used vidicon cameras to scan wide areas of the Earth's surface.

Early satellite remote sensors did not use conventional film to produce their images. Instead, the sensors digitally capture the images using a device similar to a television camera. Once captured, this data is then transmitted electronically to receiving stations found on the Earth's surface. The image below (Figure 4) is from TIROS-7 of a mid-latitude cyclone off the coast of New Zealand.

Figure 3: TIROS-1 satellite. (Source: NASA - Remote Sensing Tutorial).

Figure 4: TIROS-7 image of a mid-latitude cyclone off the coast of New Zealand, August 24, 1964. (Source: NASA - Looking at Earth From Space).

Today, the GOES (Geostationary Operational Environmental Satellite) system of satellites provides most of the remotely sensed weather information for North America. To cover the complete continent and adjacent oceans two satellites are employed in a geostationary orbit. The western half of North America and the eastern Pacific Ocean is monitored by GOES-10, which is directly above the equator and 135° West longitude. The eastern half of North America and the western Atlantic are cover by GOES-8.

The GOES-8 satellite is located overhead of the equator and 75° West longitude. Advanced sensors aboard the GOES satellite produce a continuous data stream so images can be viewed at any instance. The imaging sensor produces visible and infrared images of the Earth's terrestrial surface and oceans (Figure 5). Infrared images can depict weather conditions even during the night. Another sensor aboard the satellite can determine vertical temperature profiles, vertical moisture profiles, total precipitable water, and atmospheric stability.

Figure 5: Color image from GOES-8 of hurricanes Madeline and Lester off the coast of Mexico, October 17, 1998. (Source: NASA - Looking at Earth From Space).

In the 1970s, the second revolution in remote sensing technology began with the deployment of the Landsat satellites. Since this 1972, several generations of Landsat satellites with their Multispectral Scanners (MSS) have been providing continuous coverage of the Earth for almost 30 years. Current, Landsat satellites orbit the Earth's surface at an altitude of approximately 700 kilometers. Spatial resolution of objects on the ground surface is 79 x 56 meters. Complete coverage of the globe requires 233 orbits and occurs every 16 days.

The Multispectral Scanner records a zone of the Earth's surface that is 185 kilometers wide in four wavelength bands: band 4 at 0.5 to 0.6 micrometers, band 5 at 0.6 to 0.7 micrometers, band 6 at 0.7 to 0.8 micrometers, and band 7 at 0.8 to 1.1 micrometers. Bands 4 and 5 receive the green and red wavelengths in the visible light range of the electromagnetic spectrum. The last two bands image near-infrared wavelengths.

A second sensing system was added to Landsat satellites launched after 1982. This imaging system, known as the Thematic Mapper, records seven wavelength bands from the visible to far-infrared portions of the electromagnetic spectrum (Figure 6). In addition, the ground resolution of this sensor was enhanced to 30 x 20 meters. This modification allows for greatly improved clarity of imaged objects.

Figure 6: The Landsat 7 enhanced Thematic Mapper instrument. (Source: Landsat 7 Home Page).

The usefulness of satellites for remote sensing has resulted in several other organizations launching their own devices. In France, the SPOT (Satellite Pour l'Observation de la Terre) satellite program has launched five satellites since 1986. Since 1986, SPOT satellites have produced more than 10 million images. SPOT satellites use two different sensing systems to image the planet.

One sensing system produces black and white panchromatic images from the visible band (0.51 to 0.73 micrometers) with a ground resolution of 10 x 10 meters. The other sensing device is multispectral capturing green, red, and reflected infrared bands at 20 x 20 meters (Figure 7). SPOT-5, which was launched in 2002, is much improved from the first four versions of SPOT satellites. SPOT-5 has a maximum ground resolution of 2.5 x 2.5 meters in both panchromatic mode and multispectral operation.

Figure 7: SPOT false-color image of the southern portion of Manhatten Island and part of Long Island, New York. The bridges on the image are (left to right): Brooklyn Bridge, Manhattan Bridge, and the Williamsburg Bridge. (Source: SPOT Image).

Radarsat-1 was launched by the Canadian Space Agency in November, 1995. As a remote sensing device, Radarsat is quite different from the Landsat and SPOT satellites. Radarsat is an active remote sensing system that transmits and receives microwave radiation. Landsat and SPOT sensors passively measure reflected radiation at wavelengths roughly equivalent to those detected by our eyes.

Radarsat's microwave energy penetrates clouds, rain, dust, or haze and produces images regardless of the Sun's illumination allowing it to image in darkness. Radarsat images have a resolution between 8 to 100 meters. This sensor has found important applications in crop monitoring, defence surveillance, disaster monitoring, geologic resource mapping, sea-ice mapping and monitoring, oil slick detection, and digital elevation modeling (Figure 8).

Figure 8: Radarsat image acquired on March 21, 1996, over Bathurst Island in Nunavut, Canada. This image shows Radarsat's ability to distinguish different types of bedrock. The light shades on this image (C) represent areas of limestone, while the darker regions (B) are composed of sedimentary siltstone. The very dark area marked A is Bracebridge Inlet which joins the Arctic ocean. (Source: Canadian Centre for Remote Sensing - Geological Mapping Bathurst Island, Nunavut, Canada March 21, 1996).

Principles of Object Identification

Most people have no problem identifying objects from photographs taken from an oblique angle. Such views are natural to the human eye and are part of our everyday experience. However, most remotely sensed images are taken from an overhead or vertical perspective and from distances quite removed from ground level. Both of these circumstances make the interpretation of natural and human-made objects somewhat difficult. In addition, images obtained from devices that receive and capture electromagnetic wavelengths outside human vision can present views that are quite unfamiliar.

To overcome the potential difficulties involved in image recognition, professional image interpreters use a number of characteristics to help them identify remotely sensed objects. Some of these characteristics include:

Shape: this characteristic alone may serve to identify many objects. Examples include the long linear lines of highways, the intersecting runways of an airfield, the perfectly rectangular shape of buildings, or the recognizable shape of an outdoor baseball diamond (Figure 9).

Figure 9: Yankee stadium in Bronx, New York. Baseball stadiums have an obvious shape that can be easily recognized even from vertical aerial photographs. (Source: Google Earth).

Size: noting the relative and absolute sizes of objects is important in their identification. The scale of the image determines the absolute size of an object. As a result, it is very important to recognize the scale of the image to be analyzed.
Image Tone or Color: all objects reflect or emit specific signatures of electromagnetic radiation. In most cases, related types of objects emit or reflect similar wavelengths of radiation. Also, the types of recording device and recording media produce images that are reflective of their sensitivity to particular range of radiation. As a result, the interpreter must be aware of how the object being viewed will appear on the image examined. For example, on color infrared images vegetation has a color that ranges from pink to red rather than the usual tones of green.
Pattern: many objects arrange themselves in typical patterns. This is especially true of human-made phenomena. For example, orchards have a systematic arrangement imposed by a farmer, while natural vegetation usually has a random or chaotic pattern (Figure 10).

Figure 10: Black and white aerial photograph of natural coniferous vegetation (left) and adjacent apple orchards (center and right).

Shadow: shadows can sometimes be used to get a different view of an object. For example, an overhead photograph of a towering smokestack or a radio transmission tower normally presents an identification problem. This difficulty can be over come by photographing these objects at Sun angles that cast shadows. These shadows then display the shape of the object on the ground. Shadows can also be a problem to interpreters because they often conceal things found on the Earth's surface.
Texture: imaged objects display some degree of coarseness or smoothness. This characteristic can sometimes be useful in object interpretation. For example, we would normally expect to see textural differences when comparing an area of grass with a field corn. Texture, just like object size, is directly related to the scale of the image.

CITATION: Pidwirny, M. (2006). "Introduction to Geographic Information Systems". Fundamentals of Physical Geography, 2nd Edition. 30/1/2012.

LOCATION, DISTANCE, AND DIRECTION ON MAP

noreply@blogger.com (Unknown) — Sun, 29 Jan 2012 17:26:00 +0000

Location on Maps

Most maps allow us to specify the location of points on the Earth's surface using a coordinate system. For a two-dimensional map, this coordinate system can use simple geometric relationships between the perpendicular axes on a grid system to define spatial location. Figure 1 illustrates how the location of a point can be defined on a coordinate system.

Figure 1: A grid coordinate system defines the location of points from the distance traveled along two perpendicular axes from some stated origin. In the example above, the two axes are labeled X and Y. The origin is located in the lower left hand corner. Unit distance traveled along each axis from the origin is shown. In this coordinate system, the value associated with the X-axis is given first, following by the value assigned from the Y-axis. The location represented by the star has the coordinates 7 (X-axis), 4 (Y-axis).

Two types of coordinate systems are currently in general use in geography: the geographical coordinate system and the rectangular (also called Cartesian) coordinate system.

Geographical Coordinate System

The geographical coordinate system measures location from only two values, despite the fact that the locations are described for a three-dimensional surface. The two values used to define location are both measured relative to the polar axis of the Earth. The two measures used in the geographic coordinate system are called latitude and longitude.

Figure 2: Lines of latitude or parallels are drawn parallel to the equator (shown in red) as circles that span the Earth's surface. These parallels are measure in degrees (°). There are 90 angular degrees of latitude from the equator to each of the poles. The equator has an assigned value of 0°. Measurements of latitude are also defined as being either north or south of equator to distinguish the hemisphere of their location. Lines of longitude or meridians are circular arcs that meet at the poles. There are 180° of longitude either side of a starting meridian which is known the Prime Meridian. The Prime Meridian has a designated value of 0°. Measurements of longitude are also defined as being either west or east of the Prime Meridian.

Latitude measures the north-south position of locations on the Earth's surface relative to a point found at the center of the Earth (Figure 2). This central point is also located on the Earth's rotational or polar axis. The equator is the starting point for the measurement of latitude. The equator has a value of zero degrees. A line of latitude or parallel of 30° North has an angle that is 30° north of the plane represented by the equator (Figure 3). The maximum value that latitude can attain is either 90° North or South. These lines of latitude run parallel to the rotational axis of the Earth.

Figure 3: Measurement of latitude and longitude relative to the equator and the Prime Meridian and the Earth's rotational or polar axis.

Longitude measures the west-east position of locations on the Earth's surface relative to a circular arc called the Prime Meridian (Figure 2). The position of the Prime Meridian was determined by international agreement to be in-line with the location of the former astronomical observatory at Greenwich, England. Because the Earth's circumference is similar to circle, it was decided to measure longitude in degrees. The number of degrees found in a circle is 360.

The Prime Meridian has a value of zero degrees. A line of longitude or meridian of 45° West has an angle that is 45° west of the plane represented by the Prime Meridian (Figure 3). The maximum value that a meridian of longitude can have is 180° which is the distance halfway around a circle. This meridian is called the International Date Line. Designations of west and east are used to distinguish where a location is found relative to the Prime Meridian. For example, all of the locations in North America have a longitude that is designated west.

Universal Transverse Mercator System (UTM)

Another commonly used method to describe location on the Earth is the Universal Transverse Mercator (UTM) grid system. This rectangular coordinate system is metric, incorporating the meter as its basic unit of measurement. UTM also uses the Transverse Mercator projection system to model the Earth's spherical surface onto a two-dimensional plane. The UTM system divides the world's surface into 60 - six degree longitude wide zones that run north-south (Figure 5).

These zones start at the International Date Line and are successively numbered in an eastward direction (Figure 5). Each zone stretches from 84° North to 80° South (Figure 4). In the center of each of these zones is a central meridian. Location is measured in these zones from a false origin which is determined relative to the intersection of the equator and the central meridian for each zone. For locations in the Northern Hemisphere, the false origin is 500,000 meters west of the central meridian on the equator. Coordinate measurements of location in the Northern Hemisphere using the UTM system are made relative to this point in meters in eastings (longitudinal distance) and northings (latitudinal distance).

The point defined by the intersection of 50° North and 9° West would have a UTM coordinate of Zone 29, 500000 meters east (E), 5538630 meters north (N) (see Figures 4 and 5). In the Southern Hemisphere, the origin is 10,000,000 meters south and 500,000 meters west of the equator and central meridian, respectively. The location found at 50° South and 9° West would have a UTM coordinate of Zone 29, 500000 meters E, 4461369 meters N (remember that northing in the Southern Hemisphere is measured from 10,000,000 meters south of the equator - see Figures 4 and 5).

Figure 4: The following illustration describes the characteristics of the UTM zone "29" found between 12 to 6° West longitude. Note that the zone has been split into two halves. The half on the left represents the area found in the Northern Hemisphere. The Southern Hemisphere is located on the right. The blue line represents the central meridian for this zone. Locations measurements for this zone are calculated relative to a false origin. In the Northern Hemisphere, this origin is located 500,000 meters west of the equator. The Southern Hemisphere UTM measurements are determined relative to a origin located at 10,000,000 meters south and 500,000 meters west of the equator and central meridian, respectively.

The UTM system has been modified to make measurements less confusing. In this modification, the six degree wide zones are divided into smaller pieces or quadrilaterals that are eight degrees of latitude tall. Each of these rows is labeled, starting at 80° South, with the letters C to X consecutively with I and O being omitted (Figure 2b-5). The last row X differs from the other rows and extends from 72 to 84° North latitude (twelve degrees tall). Each of the quadrilaterals or grid zones are identified by their number/letter designation. In total, 1200 quadrilaterals are defined in the UTM system.

The quadrilateral system allows us to further define location using the UTM system. For the location 50° North and 9° West, the UTM coordinate can now be expressed as Grid Zone 29U, 500000 meters E, 5538630 meters N.

Figure 5: The UTM system also uses a grid system to break the Earth up into 1200 quadrilaterals. To keep the illustration manageable, most of these zones have been excluded. Designation of each quadrilaterals is accomplished with a number-letter system. Along the horizontal bottom, the six degree longitude wide zones are numbered, starting at 180° West longitude, from 1 to 60. The twenty vertical rows are assigned letters C to X with I and O excluded. The letter, C, begins at 80° South latitude. Note that the rows are 8 degrees of latitude wide, except for the last row X which is 12 degrees wide. According to the reference system, the bright green quadrilateral has the grid reference 29V (note that in this system west-east coordinate is given first, followed by the south-north coordinate). This grid zone is found between 56 and 64° North latitude and 6 and 12° West longitude.

Each UTM quadrilateral is further subdivided into a number of 100,000 by 100,000 meter zones. These subdivisions are coded by a system of letter combinations where the same two-letter combination is not repeated within 18 degrees of latitude and longitude. Within each of the 100,000 meter squares one can specify location to one-meter accuracy using a 5 digit eastings and northings reference system.

The UTM grid system is displayed on all United States Geological Survey (USGS) and National Topographic Series (NTS) of Canada maps. On USGS 7.5-minute quadrangle maps (1:24,000 scale), 15-minute quadrangle maps (1:50,000, 1:62,500, and standard-edition 1:63,360 scales), and Canadian 1:50,000 maps the UTM grid lines are drawn at intervals of 1,000 meters, and are shown either with blue ticks at the edge of the map or by full blue grid lines.

On USGS maps at 1:100,000 and 1:250,000 scale and Canadian 1:250,000 scale maps a full UTM grid is shown at intervals of 10,000 meters. Figure 2b-6 describes how the UTM grid system can be used to determine location on a 1:50,000 National Topographic Series of Canada map.

Figure 6: The top left hand corner the "Tofino" 1:50,000 National Topographic Series of Canada map is shown above. The blue lines and associated numbers on the map margin are used to determine location by way of the UTM grid system. Abbreviated UTM 1,000-meter values or principle digits are shown by numbers on the map margin that vary from 0 to 100 (100 is actually given the value 00). In each of the corners of the map, two of the principle digits are expressed in their full UTM coordinate form. On the image we can see 283000 m E. and 5458000 m N. The red dot is found in the center of the grid defined by principle numbers 85 to 86 easting and 57 to 58 northing. A more complete UTM grid reference for this location would be 285500 m E. and 5457500 m N. Information found on the map margin also tells us (not shown) that the area displayed is in Grid Zone 10U and the 100,000 m squares BK and CK are located on this map.

Distance on Maps

We have learned that depicting the Earth's three-dimensional surface on a two-dimensional map creates a number of distortions that involve distance, area, and direction. It is possible to create maps that are somewhat equidistance. However, even these types of maps have some form of distance distortion. Equidistance maps can only control distortion along either lines of latitude or lines of longitude. Distance is often correct on equidistance maps only in the direction of latitude.

On a map that has a large scale, 1:125,000 or larger, distance distortion is usually insignificant. An example of a large-scale map is a standard topographic map. On these maps measuring straight line distance is simple. Distance is first measured on the map using a ruler. This measurement is then converted into a real world distance using the map's scale. For example, if we measured a distance of 10 centimeters on a map that had a scale of 1:10,000, we would multiply 10 (distance) by 10,000 (scale). Thus, the actual distance in the real world would be 100,000 centimeters.

Measuring distance along map features that are not straight is a little more difficult. One technique that can be employed for this task is to use a number of straight-line segments. The accuracy of this method is dependent on the number of straight-line segments used (Figure 7). Another method for measuring curvilinear map distances is to use a mechanical device called an opisometer. This device uses a small rotating wheel that records the distance traveled. The recorded distance is measured by this device either in centimeters or inches.

Figure 7: Measurement of distance on a map feature using straight-line segments.

Direction on Maps

Like distance, direction is difficult to measure on maps because of the distortion produced by projection systems. However, this distortion is quite small on maps with scales larger than 1:125,000. Direction is usually measured relative to the location of North or South Pole. Directions determined from these locations are said to be relative to True North or True South.

The magnetic poles can also be used to measure direction. However, these points on the Earth are located in spatially different spots from the geographic North and South Pole. The North Magnetic Pole is located at 78.3° North, 104.0° West near Ellef Ringnes Island, Canada. In the Southern Hemisphere, the South Magnetic Pole is located in Commonwealth Day, Antarctica and has a geographical location of 65° South, 139° East. The magnetic poles are also not fixed overtime and shift their spatial position overtime.

Topographic maps normally have a declination diagram drawn on them (Figure 8). On Northern Hemisphere maps, declination diagrams describe the angular difference between Magnetic North and True North. On the map, the angle of True North is parallel to the depicted lines of longitude. Declination diagrams also show the direction of Grid North. Grid North is an angle that is parallel to the easting lines found on the Universal Transverse Mercator (UTM) grid system (Figure 8).

Figure 8: This declination diagram describes the angular difference between Grid, True, and Magnetic North. This illustration also shows how angles are measured relative grid, true, and magnetic azimuth.

In the field, the direction of features is often determined by a magnetic compass which measures angles relative to Magnetic North. Using the declination diagram found on a map, individuals can convert their field measures of magnetic direction into directions that are relative to either Grid or True North. Compass directions can be described by using either the azimuth system or the bearing system. The azimuth system calculates direction in degrees of a full circle. A full circle has 360 degrees (Figure 9). In the azimuth system, north has a direction of either the 0 or 360°. East and west have an azimuth of 90° and 270°, respectively. Due south has an azimuth of 180°.

Figure 9: Azimuth system for measuring direction is based on the 360 degrees found in a full circle. The illustration shows the angles associated with the major cardinal points of the compass. Note that angles are determined clockwise from north.

The bearing system divides direction into four quadrants of 90 degrees. In this system, north and south are the dominant directions. Measurements are determined in degrees from one of these directions. The measurement of two angles based on this system are described in Figure 10.

Figure 10: The bearing system uses four quadrants of 90 degrees to measure direction. The illustration shows two direction measurements. These measurements are made relative to either north or south. North and south are given the measurement 0 degrees. East and west have a value of 90 degrees. The first measurement (green) is found in the north - east quadrant. As a result, its measurement is north 75 degrees to the east or N75°E. The first measurement (orange) is found in the south - west quadrant. Its measurement is south 15 degrees to the west or S15°W.

Global Positioning Systems

Determination of location in field conditions was once a difficult task. In most cases, it required the use of a topographic map and landscape features to estimate location. However, technology has now made this task very simple. Global Positioning Systems (GPS) can calculate one's location to an accuracy of about 30-meters (Figure 11).

These systems consist of two parts: a GPS receiver and a network of many satellites. Radio transmissions from the satellites are broadcasted continually. The GPS receiver picks up these broadcasts and through triangulation calculates the altitude and spatial position of the receiving unit. A minimum of three satellite is required for triangulation.

Figure 11: Handheld Global Positioning Systems (GPS). GPS receivers can determine latitude, longitude, and elevation anywhere on or above the Earth's surface from signals transmitted by a number of satellites. These units can also be used to determine direction, distance traveled, and determine routes of travel in field situations.

CITATION: Pidwirny, M. (2006). "Location, Distance, and Direction on Maps". Fundamentals of Physical Geography, 2nd Edition. 29/1/2012.

MAP

noreply@blogger.com (Unknown) — Sun, 29 Jan 2012 16:43:00 +0000

A map can be simply defined as a graphic representation of the real world. This representation is always an abstraction of reality. Because of the infinite nature of our Universe it is impossible to capture all of the complexity found in the real world. For example, topographic maps abstract the three-dimensional real world at a reduced scale on a two-dimensional plane of paper.

Maps are used to display both cultural and physical features of the environment. Standard topographic maps show a variety of information including roads, land-use classification, elevation, rivers and other water bodies, political boundaries, and the identification of houses and other types of buildings. Some maps are created with very specific goals in mind.

The art of map construction is called cartography. People who work in this field of knowledge are called cartographers. The construction and use of maps has a long history. Some academics believe that the earliest maps date back to the fifth or sixth century BC. Even in these early maps, the main goal of this tool was to communicate information.

Early maps were quite subjective in their presentation of spatial information. Maps became more objective with the dawn of Western science. The application of scientific method into cartography made maps more ordered and accurate. Today, the art of map making is quite a sophisticated science employing methods from cartography, engineering, computer science, mathematics, and psychology.

Cartographers classify maps into two broad categories:

Reference maps : Reference maps normally show natural and human-made objects from the geographical environment with an emphasis on location. Examples of general reference maps include maps found in atlases and topographic maps.

Thematic maps : Thematic maps are used to display the geographical distribution of one phenomenon or the spatial associations that occur between a number of phenomena.

Map Projection

The shape of the Earth's surface can be described as an ellipsoid. An ellipsoid is a three-dimensional shape that departs slightly from a purely spherical form. The Earth takes this form because rotation causes the region near the equator to bulge outward to space. The angular motion caused by the Earth spinning on its axis also forces the polar regions on the globe to be somewhat flattened.

Representing the true shape of the Earth's surface on a map creates some problems, especially when this depiction is illustrated on a two-dimensional surface. To overcome these problems, cartographers have developed a number of standardized transformation processes for the creation of two-dimensional maps. All of these transformation processes create some type of distortion artifact. The nature of this distortion is related to how the transformation process modifies specific geographic properties of the map. Some of the geographic properties affected by projection distortion include: distance; area; straight line direction between points on the Earth; and the bearing of cardinal points from locations on our planet.

The illustrations below show some of the common map projections used today. The first two-dimensional projection shows the Earth's surface as viewed from space (Figure 2a-1). This orthographic projection distorts distance, shape, and the size of areas. Another serious limitation of this projection is that only a portion of the Earth's surface can be viewed at any one time.

The second illustration displays a Mercator projection of the Earth (Figure 2a-2). On a Mercator projection, the north-south scale increases from the equator at the same rate as the corresponding east-west scale. As a result of this feature, angles drawn on this type of map are correct. Distortion on a Mercator map increases at an increasing rate as one moves toward higher latitudes. Mercator maps are used in navigation because a line drawn between two points of the Earth has true direction. However, this line may not represent the shortest distance between these points.

Figure 2a-1: Earth as observed from a vantage point in space. This orthographic projection of the Earth's surface creates a two-dimensional representation of a three-dimensional surface. The orthographic projection distorts distance, shape, and the size of areas.

Figure 2a-2: Mercator map projection. The Mercator projection is one of the most common systems in use today. It was specifically designed for nautical navigation.

The Gall-Peters projection was developed to correct some of the distortion found in the Mercator system (Figure 2a-3). The Mercator projection causes area to be gradually distorted from the equator to the poles. This distortion makes middle and high latitude countries to be bigger than they are in reality. The Gall-Peters projection corrects this distortion making the area occupied by the world's nations more comparable.

Figure 2a-3: Gall-Peters projection. The Gall-Peters projection corrects the distortion of area common in Mercator maps. As a result, it removes the bias in Mercator maps that draws low latitude countries as being smaller than nations in middle and high latitudes. This projection has been officially adopted by a number of United Nations organizations.

The Miller Cylindrical projection is another common two-dimensional map used to represent the entire Earth in a rectangular area (Figure 2a-4). In this project, the Earth is mathematically projected onto a cylinder tangent at the equator. This projection in then unrolled to produce a flat two-dimensional representation of the Earth's surface. This projection reduces some of the scale exaggeration present in the Mercator map. However, the Miller Cylindrical projection describes shapes and areas with considerable distortion and directions are true only along the equator.

Figure 2a-4: The Miller Cylindrical projection.

Robinson projection was developed to show the entire Earth with less distortion of area. However, this feature requires a trade off in terms of inaccurate map direction and distance.

Figure 2a-5: Robinson's projection. This projection is common in maps that require somewhat accurate representation of area. This map projection was originally developed for Rand McNally and Company in 1961.

The Mollweide projection improves on the Robinson projection and has less area distortion (Figure 2a-6).

Figure 2a-6: Mollweide projection. On this projection the only parallels (line of latitude) drawn of true length are 40° 40' North and South. From the equator to 40° 40' North and South the east-west scale is illustrated too small. From the poles to 40° 40' North and South the east-west scale is illustrated too large.

Sinusoidal Equal-Area projection presented presents areas on a map that are proportional to the same areas on the actual surface of the Earth (Figure 2a-7). However, this Sinusoidal Equal-Area projection suffers from distance, shape, and direction distortions.

Figure 2a-7: Sinusoidal Equal-Area projection.

Map Scale

Maps are rarely drawn at the same scale as the real world. Most maps are made at a scale that is much smaller than the area of the actual surface being depicted. The amount of reduction that has taken place is normally identified somewhere on the map. This measurement is commonly referred to as the map scale. Conceptually, we can think of map scale as the ratio between the distance between any two points on the map compared to the actual ground distance represented. This concept can also be expressed mathematically as:

On most maps, the map scale is represented by a simple fraction or ratio. This type of description of a map's scale is called a representative fraction. For example, a map where one unit (centimeter, meter, inch, kilometer, etc.) on the illustration represents 1,000,000 of these same units on the actual surface of the Earth would have a representative fraction of 1/1,000,000 (fraction) or 1:1,000,000 (ratio). Of these mathematical representations of scale, the ratio form is most commonly found on maps.

Scale can also be described on a map by a verbal statement. For example, 1:1,000,000 could be verbally described as "1 centimeter on the map equals 10 kilometers on the Earth's surface" or "1 inch represents approximately 16 miles".

Most maps also use graphic scale to describe the distance relationships between the map and the real world. In a graphic scale, an illustration is used to depict distances on the map in common units of measurement. Graphic scales are quite useful because they can be used to measure distances on a map quickly.

Figure 2a-8: The following graphic scale was drawn for map with a scale of 1:250,000. In the illustration distances in miles and kilometers are graphically shown.

Maps are often described, in a relative sense, as being either small scale or large scale. Figure 2a-9 helps to explain this concept. In Figure 2a-9, we have maps representing an area of the world at scales of 1:100,000, 1:50,000, and 1:25,000. Of this group, the map drawn at 1:100,000 has the smallest scale relative to the other two maps. The map with the largest scale is map C which is drawn at a scale of 1:25,000.

Figure 2a-9: The following three illustrations describe the relationship between map scale and the size of the ground area shown at three different map scales. The map on the far left has the smallest scale, while the map on the far right has the largest scale. Note what happens to the amount of area represented on the maps when the scale is changed. A doubling of the scale (1:100,000 to 1:50,000 and 1:50,000 to 1:25,000) causes the area shown on the map to be reduced to 25% or one-quarter.

CITATION: Pidwirny, M. (2006). "Introduction to Maps". Fundamentals of Physical Geography, 2nd Edition. 29/1/2012.

EARTH - SUN GEOMETRY

noreply@blogger.com (Unknown) — Sun, 29 Jan 2012 13:14:00 +0000

Earth Rotation and Revolution

The term Earth rotation refers to the spinning of our planet on its axis. Because of rotation, the Earth's surface moves at the equator at a speed of about 467 m per second or slightly over 1675 km per hour. If you could look down at the Earth's North Pole from space you would notice that the direction of rotation is counter-clockwise (Figure 6h-1). The opposite is true if the Earth is viewed from the South Pole. One rotation takes exactly twenty-four hours and is called a mean solar day. The Earth’s rotation is responsible for the daily cycles of day and night. At any one moment in time, one half of the Earth is in sunlight, while the other half is in darkness. The edge dividing the daylight from night is called the circle of illumination. The Earth’s rotation also creates the apparent movement of the Sun across the horizon.

Figure 6h-1: The movement of the Earth about its axis is known as rotation. The direction of this movement varies with the viewer’s position. From the North Pole the rotation appears to move in a counter-clockwise fashion. Looking down at the South Pole the Earth’s rotation appears clockwise.

The orbit of the Earth around the Sun is called an Earth revolution. This celestial motion takes 365.26 days to complete one cycle. Further, the Earth's orbit around the Sun is not circular, but oval or elliptical (see Figure 6h-2). An elliptical orbit causes the Earth's distance from the Sun to vary over a year. Yet, this phenomenon is not responsible for the Earth’s seasons!

This variation in the distance from the Sun causes the amount of solar radiation received by the Earth to annually vary by about 6%. Figure 6h-2 illustrates the positions in the Earth’s revolution where it is closest and farthest from the Sun. On January 3, perihelion, the Earth is closest to the Sun (147.3 million km). The Earth is farthest from the Sun on July 4, or aphelion (152.1 million km). The average distance of the Earth from the Sun over a one-year period is about 149.6 million km.

Figure 6h-2: Position of the equinoxes, solstices, aphelion, and perihelion relative to the Earth's orbit around the Sun.

Tilt of the Earth's Axis

The ecliptic plane can be defined as a two-dimensional flat surface that geometrically intersects the Earth's orbital path around the Sun. On this plane, the Earth's axis is not at right angles to this surface, but inclined at an angle of about 23.5° from the perpendicular. Figure 6h-3 shows a side view of the Earth in its orbit about the Sun on four important dates: June solstice, September equinox, December solstice, and March equinox. Note that the angle of the Earth's axis in relation to the ecliptic plane and the North Star on these four dates remains unchanged.

Yet, the relative position of the Earth's axis to the Sun does change during this cycle. This circumstance is responsible for the annual changes in the height of the Sun above the horizon. It also causes the seasons, by controlling the intensity and duration of sunlight received by locations on the Earth.Figure 6h-4 shows an overhead view of this same phenomenon. In this view, we can see how the circle of illumination changes its position on the Earth’s surface. During the two equinoxes, the circle of illumination cuts through the North Pole and the South Pole. On the June solstice, the circle of illumination is tangent to the Arctic Circle (66.5° N) and the region above this latitude receives 24 hours of daylight. The Arctic Circle is in 24 hours of darkness during the December solstice.

Figure 6h-3:The Earth’s rotational axis is tilted 23.5° from the red line drawn perpendicular to the ecliptic plane. This tilt remains the same anywhere along the Earth’s orbit around the Sun. Seasons are appropriate only for the Northern Hemisphere.

Figure 6h-4: Annual change in the position of the Earth in its revolution around the Sun. In this graphic, we are viewing the Earth from a position in space that is above the North Pole (yellow dot) at the summer solstice, the winter solstice, and the two equinoxes. Note how the position of the North Pole on the Earth's surface does not change. However, its position relative to the Sun does change and this shift is responsible for the seasons. The red circle on each of the Earths represents the Arctic Circle (66.5 degrees N). During the June solstice, the area above the Arctic Circle is experiencing 24 hours of daylight because the North Pole is tilted 23.5 degrees toward the Sun. The Arctic Circle experiences 24 hours of night when the North Pole is tilted 23.5 degrees away from the Sun in the December solstice. During the two equinoxes, the circle of illumination cuts through the polar axis and all locations on the Earth experience 12 hours of day and night. Seasons are appropriate only for the Northern Hemisphere.

On June 21 or 22 the Earth is positioned in its orbit so that the North Pole is leaning 23.5° toward the Sun. During the June solstice (also called the summer solstice in the Northern Hemisphere), all locations north of the equator have day lengths greater than twelve hours, while all locations south of the equator have day lengths less than twelve hours (see Table 6h-2). On December 21 or 22 the Earth is positioned so that the South Pole is leaning 23.5 degrees toward the Sun. During the December solstice (also called the winter solstice in the Northern Hemisphere), all locations north of the equator have day lengths less than twelve hours, while all locations south of the equator have day lengths exceeding twelve hours (see Table 6h-2).

Figure 6h-5: During the June solstice the Earth's North Pole is tilted 23.5 degrees towards the Sun relative to the circle of illumination. This phenomenon keeps all places above a latitude of 66.5 degrees N in 24 hours of sunlight, while locations below a latitude of 66.5 degrees S are in darkness. The North Pole is tilted 23.5 degrees away from the Sun relative to the circle of illumination during the December solstice. On this date, all places above a latitude of 66.5 degrees N are now in darkness, while locations below a latitude of 66.5 degrees S receive 24 hours of daylight.

On September 22 or 23, also called the autumnal equinox in the Northern Hemisphere, neither pole is tilted toward or away from the Sun. In the Northern Hemisphere, March 20 or 21 marks the arrival of the vernal equinox or spring when once again the poles are not tilted toward or away from the Sun. Day lengths on both of these days, regardless of latitude, are exactly 12 hours.

Figure 6h-6: During the equinoxes, the axis of the Earth is not tilted toward or away from the Sun and the circle of illumination cuts through the poles. This situation does not suggest that the 23.5 degree tilt of the Earth no longer exists. The vantage point of this graphic shows that the Earth's axis is inclined 23.5 degrees toward the viewer for both dates (see Figures 6h-3 and 6h-4). The red circles shown in the graphic are the Arctic Circle.

Axis Tilt and Solar Altitude

The annual change in the relative position of the Earth's axis in relationship to the Sun causes the height of the Sun or solar altitude to vary in our skies. Solar altitude is normally measured from either the southern or northern point along the horizon and begins at zero degrees. Maximum solar altitude occurs when the Sun is directly overhead and has a value of 90°. The total variation in maximum solar altitude for any location on the Earth over a one-year period is 47° (Earth’s tilt 23.5° x 2 = 47°).

This variation is due to the annual changes in the relative position of the Earth to the Sun. At 50 degrees North, maximum solar altitude varies from 63.5 degrees on the June solstice to 16.5 degrees on the December solstice (Figure 6h-10). Maximum solar height at the equator goes from 66.5 degrees above the northern end of the horizon during the June solstice, to directly overhead on the September equinox, and then down to 66.5 degrees above the southern end of the horizon during the December solstice (Figure 6h-11).

Figure 6h-10: Variations in solar altitude at solar noon for 50 degrees North during the June solstice, equinox, and December solstice.

Figure 6h-11: Variations in solar altitude at solar noon for the equator during the June solstice, equinox, and December solstice.

The location on the Earth where the Sun is directly overhead at solar noon is known as the subsolar point. The subsolar point occurs on the equator during the two equinoxes (Figures 6h-11 and 6h-12). On these dates, the equator is lined up with the ecliptic plane and the poles are in line with the circle of illumination (Figure 6h-6). During the summer solstice, the subsolar point moves to the Tropic of Cancer (23.5° N) because at this time the North Pole is inclined 23.5° toward the Sun (Figures 6h-12 and 6h-13). Figure 6h-13 shows how the subsolar point gradually changes from one day to the next over a period of one-year. Note that on this graph, the subsolar point is located at the Tropic of Capricorn(23.5° S) during the December solstice when the South Pole is angled 23.5° toward the Sun (Figure 6h-5).

Figure 6h-12: Relationship of maximum Sun height to latitude for the equinox (left) and June solstice (right). The red values on the right of the globes are maximum solar altitudes at solar noon. Black numbers on the left indicate the location of the Equator, Tropic of Cancer (23.5 degrees N), Tropic of Capricorn (23.5 degrees S), Arctic Circle (66.5 degrees N), and the Antarctic Circle (66.5 degrees S). The location of the North and South Poles are also identified. During the equinox, the equator is the location on the Earth with a Sun angle of 90 degrees for solar noon. Note how maximum Sun height declines with latitude as you move away from the Equator. For each degree of latitude traveled maximum Sun height decreases by the same amount. At equinox, you can also calculate the noon angle by subtracting the location's latitude from 90. During the summer solstice, the Sun is now directly overhead at the Tropic of Cancer. All locations above this location have maximum Sun heights that are 23.5 degrees higher from the equinox situation. Places above the Arctic Circle are in 24 hours of daylight. Below the Tropic of Cancer the noon angle of the Sun drops one degree in height for each degree of latitude traveled. At the Antarctic Circle, maximum Sun height becomes 0 degrees and locations south of this point on the Earth are in 24 hours of darkness.

Figure 6h-13: Angle of the Sun’s declination and latitude of the subsolar point throughout the year. Seasons are for the Northern Hemisphere.

The following table describes the changes in solar altitude at solar noon for the two solstices and equinoxes. All measurements are in degrees (horizon has 180 degrees from True North to True South) and are measured from either True North or True South (whatever is closer).

Table 6h-1: Maximum Sun altitudes for selected latitudes during the two solstices and equinoxes.

Location's Latitude	March Equinox March 20/21	June Solstice June 21/22	September Equinox September 22/23	December Solstice December 21/22
90 N	0 degrees	23.5 degrees	0 degrees	- 23.5 degrees
70 N	20 degrees	43.5 degrees	20 degrees	-3.5 degrees
66.5 N	23.5 degrees	47 degrees	23.5 degrees	0 degrees
60 N	30 degrees	53.5 degrees	30 degrees	6.5 degrees
50 N	40 degrees	63.5 degrees	40 degrees	16.5 degrees
23.5 N	66.5 degrees	90 degrees	66.5 degrees	43 degrees
0 degrees	90 degrees	66.5 degrees	90 degrees	66.5 degrees
23.5 S	66.5 degrees	43 degrees	66.5 degrees	90 degrees
50 S	40 degrees	16.5 degrees	40 degrees	63.5 degrees
60 S	30 degrees	6.5 degrees	30 degrees	53.5 degrees
66.5 S	23.5 degrees	0 degrees	23.5 degrees	47 degrees
70 S	20 degrees	-3.5 degrees	20 degrees	43.5 degrees
90 S	0 degrees	- 23.5 degrees	0 degrees	23.5 degrees

Finally, the altitude of the Sun at solar noon can also be calculated with the following simple equation:

Altitude A = 90 - Latitude L +/- Declination D

In this equation, L is the latitude of the location in degrees and D is the declination. The equation is simplified to A = 90 - L if Sun angle determinations are being made for either equinox date. If the Sun angle determination is for a solstice date, declination (D) is added to latitude (L) if the location is experiencing summer (northern latitudes = June solstice; southern latitudes = December solstice) and subtracted from latitude (L) if the location is experiencing winter (northern latitudes = December solstice; southern latitudes = June solstice).

All answers from this equation are given relative to True North for southern latitudes and True South for northern latitudes. For our purposes only the declinations of the two solstices and two equinoxes are important. These values are: June solstice D=23.5, December solstice D=23.5, March equinox D=0, and Septemeber equinox D=0. When using the above equation in tropical latitudes, Sun altitude values greater than 90 degrees may occur for some calculations. When this occurs, the noonday Sun is actually behind you when looking towards the equator. Under these circumstances, Sun altitude should be recalculated as follows:

Altitude A = 90 - (originally calculated Altitude A - 90)

CITATION: Pidwirny, M. (2006). "Earth-Sun Geometry". Fundamentals of Physical Geography, 2nd Edition. 29/1/2012.

THE SOLAR SOURCE OF THE EARTH'S ENERGY

noreply@blogger.com (Unknown) — Sun, 29 Jan 2012 12:35:00 +0000

Almost all of the energy that drives the various systems (climate systems, ecosystems, hydrologic systems, etc.) found on the Earth originates from the Sun. Solar energy is created at the core of the Sun when hydrogen atoms are fused into helium by nuclear fusion. For each second of this nuclear process, 700 million tons of hydrogen are converted into 695 million tons of helium. The remaining 5 million tons are turned into electromagnetic energy that radiates from the Sun's surface out into space.

The radiative surface of the Sun, or photosphere, has an average temperature of about 5800 Kelvins. Most of the electromagnetic radiation emitted from the Sun's surface lies in the visible band centered at 0.5 µm. The total quantity of energy emitted from the Sun's surface is approximately 63,000,000 Watts per square meter (W/m2 or Wm-2).

Figure 6g-1: The Sun observed by SUMER instrument on the SOHO satellite on March 2-4, 1996. (Source: SOHO - SUMER Instrument).

The energy emitted by the Sun passes through space until it is intercepted by planets and other celestial objects. The intensity of solar radiation striking these objects is determined by a physical law known as the Inverse Square. This law merely states that the intensity of the radiation emitted from the Sun varies with the squared distance from the source. As a result of this law, if the intensity of radiation at a given distance is one unit, at twice the distance the intensity will become only one-quarter. At three times the distance, the intensity will become only one-ninth of its original intensity at a distance of one unit, and so on.

Given the amount of energy radiated by the Sun and the average Earth-Sun distance of 149.5 million kilometers, the amount of radiation intercepted by the outer limits of the atmosphere can be calculated to be around 1370 W/m2. For general purposes, the energy output of the Sun can be considered constant. This of course is not entirely true. Scientists have shown that the output of the Sun is temporally variable. Some researchers have also suggested that the increase in the average global temperature over the last century may have been solar in origin. This statement, however, is difficult to prove because accurate data on solar output of radiation only goes back to about 1978.

CITATION: Pidwirny, M. (2006). "The Solar Source of the Earth's Energy". Fundamentals of Physical Geography, 2nd Edition. 29/1/2012.

THE NATURE OF RADIATION

noreply@blogger.com (Unknown) — Sun, 29 Jan 2012 12:23:00 +0000

All objects above the temperature of absolute zero (-273.15° Celsius) radiate energy to their surrounding environment. This energy, or radiation, is emitted as electromagnetic waves that travel at the speed of light. Many different types of radiation have been identified. Each of these types is defined by its wavelength. The wavelength of electromagnetic radiation can vary from being infinitely short to infinitely long (Figure 6f-1).

Figure 6f-1: Some of the various types of electromagnetic radiation as defined by wavelength. Visible light has a spectrum that ranges from 0.40 to 0.71 micrometers (µm).

Visible light is a form of electromagnetic radiation that can be perceived by our eyes. Light has a wavelength of between 0.40 to 0.71 micrometers (µm). Figure 6f-1 illustrates that various spectral color bands that make up light. The Sun emits only a portion (44 %) of its radiation in zone. Solar radiation spans a spectrum from approximately 0.1 to 4.0 micrometers. The band from 0.1 to 0.4 micrometers is called ultraviolet radiation. About 7% of the Sun's emission is in this wavelength band. About 48% of the Sun's radiation falls in the region between 0.71 to 4.0 micrometers. This band is called the near (0.71 to 1.5 micrometers) and far infrared (1.5 to 4.0 micrometers).

The amount of electromagnetic radiation emitted by a body is directly related to its temperature. If the body is a perfect emitter (black body), the amount of radiation given off is proportional to the 4th power of its temperature as measured in Kelvin units. This natural phenomenon is described by the Stefan-Boltzmann Law. The following simple equation describes this law mathematically:

According to the Stephan-Boltzmann equation, a small increase in the temperature of a radiating body results in a large amount of additional radiation being emitted.

In general, good emitters of radiation are also good absorbers of radiation at specific wavelength bands. This is especially true of gases and is responsible for the Earth's greenhouse effect. Likewise, weak emitters of radiation are also weak absorbers of radiation at specific wavelength bands. This fact is referred to as Kirchhoff's Law. Some objects in nature have almost completely perfect abilities to absorb and emit radiation. We call these objects black bodies. The radiation characteristics of the Sun and the Earth are very close to being black bodies.

The wavelength of maximum emission of any body is inversely proportional to its absolute temperature. Thus, the higher the temperature, the shorter the wavelength of maximum emission. This phenomenon is often called Wien's Law. The following equation describes this law:

Wien's law suggests that as the temperature of a body increases, the wavelength of maximum emission becomes smaller. According to the above equation the wavelength of maximum emission for the Sun (5800 Kelvins) is about 0.5 micrometers, while the wavelength of maximum emission for the Earth (288 Kelvins) is approximately 10.0 micrometers.

A graph that describes the quantity of radiation that is emitted from a body at particular wavelengths is commonly called a spectrum. The following two graphs describe the spectrums for the Sun and Earth.

Figure 6f-2: Spectrum of the Sun. The Sun emits most of its radiation in a wavelength band between 0.1 and 4.0 micrometers (µm).

Figure 6f-3: Spectrum of the Earth. The Earth emits most of its radiation in a wavelength band between 0.5 and 30.0 micrometers (µm).

The above graphs illustrate two important points concerning the relationship between the temperature of a body and its emissions of electromagnetic radiation:

The amount of radiation emitted from a body increases exponentially with a linear rise in temperature (see above Stephan-Boltzmann's Law).
The average wavelength of electromagnetic emissions becomes shorter with increasing temperature (see above Wien's Law).

Finally, the amount of radiation passing through a specific area is inversely proportional to the square of the distance of that area from the energy source. This phenomenon is called the Inverse Square Law. Using this law we can model the effect that distance traveled has on the intensity of emitted radiation from a body like the Sun. Figure 6f-4 suggests that the intensity of radiation emitted by a body quickly diminishes with distance in a nonlinear fashion.

Figure 6f-4: Diagram illustrating the diffusion of radiation due to the Inverse Square Law.

Mathematically, the Inverse Square Law is described by the equation:

Intensity = I/d2

where I is the intensity of the radiation at 1d (see above diagram) and d is the distance traveled.

CITATION: Pidwirny, M. (2006). "The Nature of Radiation". Fundamentals of Physical Geography, 2nd Edition. 29/1/2012.

LAWS OF THERMODYNAMICS

noreply@blogger.com (Unknown) — Sun, 29 Jan 2012 11:57:00 +0000

The field of thermodynamics studies the behavior of energy flow in natural systems. From this study, a number of physical laws have been established. The laws of thermodynamics describe some of the fundamental truths of thermodynamics observed in our Universe. Understanding these laws is important to students of Physical Geography because many of the processes studied involve the flow of energy.

First Law of Thermodynamics

The first law of thermodynamics is often called the Law of Conservation of Energy. This law suggests that energy can be transferred from one system to another in many forms. Also, it can not be created or destroyed. Thus, the total amount of energy available in the Universe is constant. Einstein's famous equation (written below) describes the relationship between energy and matter:

E = mc2

In the equation above, energy (E) is equal to matter (m) times the square of a constant (c). Einstein suggested that energy and matter are interchangeable. His equation also suggests that the quantity of energy and matter in the Universe is fixed.

Second Law of Thermodynamics

Heat cannot be transfer from a colder to a hotter body. As a result of this fact of thermodynamics, natural processes that involve energy transfer must have one direction, and all natural processes are irreversible. This law also predicts that the entropy of an isolated system always increases with time. Entropy is the measure of the disorder or randomness of energy and matter in a system. Because of the second law of thermodynamics both energy and matter in the Universe are becoming less useful as time goes on. Perfect order in the Universe occurred the instant after the Big Bang when energy and matter and all of the forces of the Universe were unified.

Third Law of Thermodynamics

The third law of thermodynamics states that if all the thermal motion of molecules (kinetic energy) could be removed, a state called absolute zero would occur. Absolute zero results in a temperature of 0 Kelvins or -273.15° Celsius.

Absolute Zero = 0 Kelvins = -273.15° Celsius

The Universe will attain absolute zero when all energy and matter is randomly distributed across space. The current temperature of empty space in the Universe is about 2.7 Kelvins.

CITATION: Pidwirny, M. (2006). "Laws of Thermodynamics". Fundamentals of Physical Geography, 2nd Edition. 29/1/2012.

ENERGY AND LIFE

noreply@blogger.com (Unknown) — Sun, 29 Jan 2012 11:45:00 +0000

The capture and use of energy in living systems is dominated by two processes: photosynthesis and respiration. Through these two processes living organisms are able to capture and use all of the energy they require for their activities.

Photosynthesis

Plants can capture the electromagnetic energy from the Sun by a chemical process called photosynthesis. This chemical reaction can be described by the following simple equation:

6CO2 + 6H2O + light energy >>> C6H12O6 + 6O2

The product of photosynthesis is the carbohydrate glucose and oxygen which is released into the atmosphere. All of the sugar glucose is produced in the specialized photosynthetic cells of plants and some other organisms. Glucose is produced by chemically combining carbon dioxide and water with sunlight. This chemical reaction is catalyzed by chlorophyll acting in concert with other pigment, lipid, sugars, protein, and nucleic acid molecules.

Sugars created in photosynthesis can be later converted by the plant to starch for storage, or it can be combined with other sugar molecules to form specialized carbohydrates such as cellulose, or it can be combined with other nutrients such as nitrogen, phosphorus, and sulfur, to build complex molecules such as proteins and nucleic acids.

Because all the energy fixed by a plant is converted into sugar, it is theoretically possible to determine a plant's energy uptake by measuring the amount of sugar produced. This quantity is called gross primary productivity. Measurements of the buildup of sugar in the plant reflect gross primary productivity less respiration, or net primary productivity.

In general, animals cannot produce their own energy via photosynthesis. Instead, they capture their energy by the consumption and assimilation of the biomass of plants or other animals. Thus, animals get the energy they need for maintenance of their bodies tissues, growth, and reproduction indirectly from photosynthetic organisms.

Respiration

The oxidation of sugar by organisms is called respiration. This process occurs in both plants and animals. In most organisms, respiration releases the energy required for all metabolic processes. This chemical reaction can be described by the following simple equation:

C6H12O6 + 6O2 >>> 6CO2 + 6H2O + released energy

One of the products of respiration is energy, which is released via the chemical decomposition of glucose. Other products of this chemical reaction are carbon dioxide (CO2) and water (H2O).

CITATION: Pidwirny, M. (2006). "Energy and Life". Fundamentals of Physical Geography, 2nd Edition. 29/1/2012.

ENERGY, TEMPERATURE, AND HEAT

noreply@blogger.com (Unknown) — Sun, 29 Jan 2012 11:36:00 +0000

We have learned that energy can take on many forms. One important form of energy, relative to life on Earth, is kinetic energy. Simply defined, kinetic energy is the energy of motion. The amount of kinetic energy that a body possesses is dependent on the speed of its motion and its mass. At the atomic scale, the kinetic energy of atoms and molecules is sometimes referred to as heat energy.

Kinetic energy is also related to the concept of temperature. Temperature is defined as the measure of the average speed of atoms and molecules. The higher the temperature, the faster these particles of matter move. At a temperature of -273.15° Celsius (absolute zero) all atomic motion stops. Heat is often defined as energy in the process of being transferred from one object to another because of difference in temperature between them. Heat is commonly transferred around our planet by the processes of conduction, convection, advection, and radiation.

Some other important definitions related to energy, temperature, and heat are:

Heat Capacity - is the amount of heat energy absorbed by a substance associated to its corresponding temperature increase.
Specific Heat - is equivalent to the heat capacity of a unit mass of a substance or the heat needed to raise the temperature of one gram (g) of a substance one degree Celsius. Water requires about 4 to 5 times more heat energy to raise its temperature when compared to an equal mass of most types of solid matter. This explains why water bodies heat more slowly than adjacent land surfaces.
Sensible Heat - is heat that we can sense. A thermometer can be used to measure this form of heat. Several different scales of measurement exist for measuring sensible heat. The most common are: Celsius scale, Fahrenheit scale, and the Kelvin scale.Latent Heat - is the energy needed to change a substance to a higher state of matter. This same energy is released from the substance when the change of state (or phase) is reversed. The diagram below describes the various exchanges of heat involved with 1 gram of water.

Figure 6c-1: Latent heat exchanges of energy involved with the phase changes of water.

Figures 6c-2 and 6c-3 show the net absorption and release of latent heat energy for the Earth's surface for January and July, respectively. The highest values of flux or flow occur near the subtropical oceans where high temperatures and a plentiful supply of water encourage the evaporation of water. Negative values of latent heat flux indicate a net release of latent energy back into the environment because of the condensation or freezing of water. Values of latent heat flux are generally low over landmasses because of a limited supply of water at the ground surface.

Figure 6c-2: Mean January latent heat flux for the Earth's surface, 1959-1997. (Source of Original Modified Image: Climate Lab Section of the Environmental Change Research Group, Department of Geography, University of Oregon - Global Climate Animations).

Figure 6c-3: Mean July latent heat flux for the Earth's surface, 1959-1997. (Source of Original Modified Image: Climate Lab Section of the Environmental Change Research Group, Department of Geography, University of Oregon - Global Climate Animations).

CITATION: Pidwirny, M. (2006). "Energy, Temperature, and Heat". Fundamentals of Physical Geography, 2nd Edition. 29/1/2012.

MEASUREMENT OF ENERGY

noreply@blogger.com (Unknown) — Sun, 29 Jan 2012 11:19:00 +0000

In the previous discussion (Characteristics of Energy Matter), we developed the concept of energy. We now must be able to measure and quantify it, using a standard set of units. Worldwide, two systems of units of measurement are commoly used today: the Metric System (Systeme International) and the British System. The units of energy described in these systems are derived from a technical definition of energy used by physicists. This definition suggests that energy can be represented by the following simple equation:

Work = Force x Distance

Similar to the definition given in the previous topic, physicists view energy as the ability to do work. However, they define work as a force applied to some form of matter (object) multiplied by the distance that this object travels. Physicists commonly describe force with a unit of measurement known as a newton (after Sir Isaac Newton). A newton is equal to the force needed to accelerate (move) a mass weighting one kilogram one meter in one second in a vacuum with no friction. The work or energy required to move an object with the force of one newton over a distance of one meter is called a joule.

Some other definitions for the energy measurement units that you may come across in this textbook are as follows:

Calorie - equals the amount of heat required to raise 1 gram of pure water from 14.5 to 15.5° Celsius at standard atmospheric pressure. 1 calorie is equal to 4.1855 joules. The abreviation for calorie is cal. A kilocalorie, abbreviated kcal, is equal to a 1000 calories. 1 kilocalorie is equal to 4185 joules.
Btu - also called British thermal unit is the amount of energy required to raise the temperature of one pound of water one degree Fahrenheit.
Watt (W/m2 or Wm-2) - a metric unit of measurement of the intensity of radiation in watts over a square meter surface. One watt is equal to one joule of work per second. A kilowatt (kW) is the same as 1000 watts.

CITATION: Pidwirny, M. (2006). "Measurement of Energy". Fundamentals of Physical Geography, 2nd Edition. 29/1/2012.

CHARACTERISTIC OF ENERGY MATTER

noreply@blogger.com (Unknown) — Sun, 29 Jan 2012 11:07:00 +0000

Energy is defined simply by scientists as the capacity for doing work. Matter is the material (atoms and molecules) that constructs things on the Earth and in the Universe. Albert Einstein suggested early in this century that energy and matter are related to each other at the atomic level. Einstein theorized that it should be possible to convert matter into energy.

From Einstein's theories, scientists were able to harness the energy of matter beginning in the 1940s through nuclear fission. The most spectacular example of this process is a nuclear explosion from an atomic bomb. A more peaceful example of our use of this fact of nature is the production of electricity from controlled fission reactions in nuclear reactors.Einstein also suggested that it should be possible to transform energy into matter.

Energy and matter are also associated to each other at much larger scales of nature. Later on in this chapter, we will examine how solar radiation provides the energy to create the matter that makes up organisms. Organisms then use some of this matter to power their metabolism.

Types of Energy

Energy comes in a variety of forms. The simplest definition of the types of energy suggests that two forms exist: kinetic energy and potential energy. Kinetic energy is the energy due to motion. A rock falling from a cliff, a bee in flight, wind blowing leaves of trees, and water following over a waterfall are all examples of kinetic energy. Potential energy is the energy stored by an object that can be potentially transformed into another form of energy.

Water stored behind a dam, the chemical energy of the food we consume, and the gasoline that we putting in our cars are all examples of potential energy. Conversion of this energy occurs when the energy in food is used by an organism to energize its metabolism, when the water in the dam flows through turbines to produce electricity from motion, and when the gasoline is used in a engine to produce motion from combustion.

Some other forms of energy include heat, electricity, sound, energy of chemical reactions, magnetic attraction, energy of atomic reactions, and light. Definitions for a few of these types of energy are as follows:

Radiation - is the emission of energy from a material object in the form of electromagnetic waves and photons.
Chemical Energy - is the energy produced or consumed in chemical reactions.
Atomic Energy - is the energy released from an atomic nucleus because of a change in its subatomic mass.
Electrical Energy - is the energy produced from the force between two objects having the physical property of electrical charge.
Heat Energy - is a form of energy created by the combined internal motion of atoms in a substance.

On Earth, there are fundamentally only three ways in which energy can be transferred from one place to another: conduction, convection, and radiation. Conduction involves the adjacent transfer of heat energy from one atom to another through the mass of a gas, liquid, or solid. Conduction results in the continuous flow of heat energy along a temperature gradient from areas of higher to lower temperature. Convection involves the transfer of heat energy by way of mass movements of a substance in gas or liquid form in a vertical direction (horizontal transfer is called advection).

Convection is often seen as rising masses of gas or liquid called convection currents. It is important to note that energy transfer by way of conduction and convection depends on the presence of matter. These forms of energy transfer do not operate in the vacuum of space. Radiation is the only means of energy transfer that can occur across outer space. The transfer of radiation produced at the Sun's surface through space supplies the Earth with most of its energy.

Matter: Elements and Compounds

Matter is the material that makes up things in the Universe. All matter on the Earth is constructed of elements. Chemists have described approximately 115 different elements. Each of these elements have distinct chemical characteristics. Table 6a-1 lists some of the chemical characteristics for 48 common elements found in the Earth's continental crust.

The smallest particle that exhibits the unique chemical characteristics of an element is known as an atom. Atoms are composed of yet smaller particles known as protons, neutrons, and electrons. A proton is a subatomic particle that has significant mass and contributes a single positive electrical charge to an atom. Neutrons also have significant mass but no electrical charge. Electrons are extremely light subatomic particles having a mass that is 1/1840 of a proton. Each electron also has a negative electrical charge.

Protons and neutrons make up the nucleus of an atom. As a result, most of an atom's mass is concentrated in the nucleus. Because protons are positively charged the nucleus has a positive charge equal to the number of these subatomic particles. Electrons are found orbiting outside the nucleus at various distances based on their energy level. The area occupied by the electrons has a negative charge equal to the number of these subatomic particles. If an atom has an equal number of electrons and protons its net electrical charge is zero. If there are more electrons than protons the charge of the atom is negative. Likewise, if there are less electrons than protons the charge of the atom is positive. In both cases, the exact charge is determined by subtracting protons from electrons. As a result, 4 protons minus 6 electrons give an atomic charge of -2.

The number of protons found in the nuclei of the different types of elements is unique and is referred to as the atomic number (Table 6a-1). All atoms of a specific element have the same number of protons in their nuclei. Atomic mass number is an atom's total number of neutrons and protons. Many elements have unequal numbers of neutrons and protons in their nucleus. An element's atomic weight refers to the total weight of neutrons, protons, and electrons. For example, the atomic weight of aluminum is 26.98 (Table 6a-1). Atomic number describes the number of protons found in an atom.

For example, silver has an atomic number of 47 or 47 protons in its atom (Table 6a-1). Some elements can have variants containing different numbers of neutrons but similar numbers of protons. We call these variants isotopes. Carbon has two isotopes. Its most common form is carbon-12 which has 6 protons plus 6 neutrons. About 99% of the carbon on our planet is of this type. The isotope carbon-13 has 6 protons plus 7 neutrons. Carbon-14 is the rarest isotope of carbon containing 8 neutrons. Some isotopes are unstable and their nucleus tends to lose subatomic particles forming an element with a lower atomic mass. This process is known as radioactive decay.

Table 6a-1: Characteristics of some of the common chemical elements found in the Earth's continental crust.

Element	Chemical Symbol	Atomic Number	Common Atomic Mass Number	Atomic Weight	Percent in Continental Crust	Required for all Life	Required for Some Lifeforms	Element Type	Moderately Toxic	Extremely Toxic
Aluminum	Al	13	27	26.98	8.2300	-	X	Metalloid	-	-
Antimony	Sb	51	122	121.75	0.00002	-	-	Metalloid	-	-
Arsenic	As	33	75	74.92	0.00018	-	-	Metalloid	-	X
Barium	Ba	56	137	137.34	0.0425	-	-	Metal	-	-
Beryllium	Be	4	10	9.01	0.00028	-	-	Metal	-	X
Bismuth	Bi	83	209	208.98	0.000017	-	-	Metal	-	-
Boron	B	5	11	10.81	0.0010	-	-	Metalloid	-	-
Bromine	Br	35	80	79.91	0.00025	-	-	Nonmetal	-	-
Cadmium	Cd	48	112	112.40	0.00002	-	-	Metal	-	X
Calcium	Ca	20	40	40.08	4.1000	X	-	Metal	-	-
Carbon	C	6	12	12.01	0.0200	X	-	Nonmetal	-	-
Chlorine	Cl	17	35.5	35.45	0.0130	-	X	Nonmetal	X	-
Chromium	Cr	24	52	52.00	0.0100	-	-	Metal	X	-
Cobalt	Co	27	59	58.93	0.0025	-	X	Metal	-	-
Copper	Cu	29	63.5	63.54	0.0055	X	-	Metal	X	-
Fluorine	F	9	19	19.00	0.0625	-	X	Nonmetal	X	-
Gallium	Ga	31	70	69.72	0.0015	-	-	Metal	-	-
Germanium	Ge	32	73	72.59	0.00015	-	-	Metalloid	-	-
Gold	Au	79	197	196.97	0.0000004	-	-	Metal	-	-
Hydrogen	H	1	1	1.008	1.4000	X	-	Nonmetal	-	-
Iodine	I	53	127	126.90	0.00005	-	X	Nonmetal	-	-
Iron	Fe	26	56	55.85	5.6000	X	-	Metal	-	-
Lead	Pb	82	207	207.19	0.00125	-	-	Metal	-	X
Lithium	Li	3	6	6.94	0.0020	-	-	Metal	-	-
Magnesium	Mg	12	24	24.31	2.3000	X	-	Metal	-	-
Manganese	Mn	25	55	54.94	0.0950	X	-	Metal	-	-
Mercury	Hg	80	201	200.59	0.000008	-	-	Metal	-	X
Molybdenum	Mo	42	96	95.94	0.00015	X	-	Metal	-	-
Nickel	Ni	28	59	58.71	0.0075	-	-	Metal	-	X
Nitrogen	N	7	14	14.01	0.0020	X	-	Nonmetal	-	-
Oxygen	O	8	16	16.00	46.4000	X	-	Nonmetal	-	-
Palladium	Pd	46	106	106.40	0.000001	-	-	Metal	X	-
Phosphorus	P	15	31	30.97	0.1050	X	-	Nonmetal	-	-
Platinum	Pt	78	195	195.09	0.0000005	-	-	Metal	-	-
Potassium	K	19	39	39.10	2.1000	X	-	Metal	-	-
Rubidium	Rb	37	85.5	85.47	0.0090	-	-	Metal	-	-
Selenium	Se	34	79	78.96	0.000005	-	X	Nonmetal	X	-
Silicon	Si	14	28	28.09	28.2000	-	-	Metalloid	-	-
Silver	Ag	47	108	107.87	0.000007	-	-	Metal	-	X
Sodium	Na	11	23	22.99	2.4000	-	X	Metal	-	-
Sulfur	S	16	32	32.06	0.0260	X	-	Nonmetal	-	-
Thorium	Th	90	232	232.04	0.00096	-	-	-	-	-
Tin	Sn	50	119	118.69	0.00020	-	-	Metal	X	-
Titanium	Ti	22	48	47.90	0.5700	-	-	Metal	-	-
Tungsten	W	74	184	183.85	0.00015	-	-	Metal	-	-
Uranium	U	92	238	238.03	0.00027	-	-	-	-	-
Vanadium	V	23	51	50.94	0.0135	-	X	Metal	X	-
Zinc	Zn	30	65	65.37	0.0070	X	-	Metal	-	-

Elements can be classified as being either metals, nonmetals, or metalloids (Table 6a-1). Metals are elements that usually conduct heat and electricity and are shiny. Nonmetals do not conduct electricity that well and are normally not shiny. Metalloids have characteristics that are in between metals and nonmetals.

Elements with a net positive or negative charge are called ions. Chemists indicate the number of positive or negative charges on an ion using a superscript after the element's symbol. For example, calcium has two positive charges and is written as Ca2+. Some common negatively charged ions include nitrate (NO3-), sulfate (SO42-), and phosphate (PO43-).

Positive and negative ions are electrically attracted to each other. This mutual attraction allows for the bonding of atoms to occur forming structures of matter that are larger than just one atom. When similar atoms bond together they construct molecules. Atoms of different elements joined together form compounds (Figure 6a-1). Sodium chloride (or table salt), is an ionic compound consisting of sodium (Na+) and chloride (Cl-). In nature, it forms as a three-dimensional array of oppositely charged ions (Figure 6a-2). Many of the Earth's substances have a molecular structure similar to sodium chloride.

Figure 6a-1: Some common molecules and compounds. The molecules in the top row bond with each other by sharing electrons. The compounds in the bottom row also share electrons. However, these joins are called ionic bonds.

Figure 6a-2: Atomic representation of sodium chloride or table salt. This compound forms in nature as a highly ordered, three-dimensional network of oppositely charged ions. The bonds that form between the sodium (Na+) and (Cl-) chloride ions give this compound great internal strength allowing it to form large crystals.

Inorganic vs. Organic

Compounds and molecules constructed in living tissues are commonly called organic. Forms of matter not formed by living things are termed inorganic. Organisms like autotrophs usually create organic matter by consuming inorganic molecules and compounds from the lithosphere, hydrosphere, and atmosphere. An example of an autotroph is any photosynthesizing plant. Heterotrophs consume and assimilate other living things to create their organic matter. Herbivores and carnivores are examples of heterotrophs.

There are four general categories of organic compounds: lipids, carbohydrates, proteins, and nucleic acids.

Lipids - are composed of carbon atoms that have two hydrogen atoms attached. Lipids are commonly known as fats and oils, and belong to the family of molecules known as hydrocarbons.
Carbohydrates - are composed of carbon, oxygen, and hydrogen atoms. Some examples are sugars, starch, and cellulose.
Proteins - are organic compounds that are made primarily of carbon, hydrogen, nitrogen, and some other minor elements that are arranged into 20 different compounds known as amino acids.
Nucleic Acids - are composed primarily of different combinations of carbon, hydrogen, nitrogen, oxygen, and phosphorus. They are very complex compounds being created by the atomic linking of thousands of individual atoms. DNA or deoxyribonucleic acid, the genetic blueprint of life, is an example of a nucleic acid.

Cells

All organisms are composed of one or more of cells. Cells are the smallest self-functioning unit found in living organisms. Cells are also where the processes of metabolism and heredity occur in an organism. Cells arise by the cellular division of a previously existing cell. Biologists have differentiated two basic types of cells in organisms. Bacteria, archaea, and cyanobacteria have cells that are quite uncomplicated in terms of structure and function. Quite simply, they lack internal organization. These cells are commonly known as prokaryotes (Figure 6a-3).

Figure 6a-3: Typical prokaryote cell. These cells are about 1 to 10 micrometers in size. The cell is encased by rigid cell wall and a plasma membrane. Within the cell, the two most obvious structures are ribosomes and DNA. The DNA is not bounded by a membrane. Many prokaryote cells also have a flagellum which is used for movement.

The cells of plants and animals are more complex than those of bacteria, archaea, and cyanobacteria. We call these type of cells eukaryotes. Eukaryotic cells have a membrane enclosed nucleus which contains the organism's DNA. Plant and animal cells also contain a variety of membrane-bound structures known as organelles. Figures 6a-4 and 6a-5 describe the various structures found in typical plant and animals cells.

Eukaryotic cells also show great variation in terms of size. White blood cells of mammals are some of the smallest eukaryotic cells with a diameter between 3 to 4 micrometers. Ostrich ovum are very large cells with a diameter of about 100 micrometers.

Figure 6a-4: Typical plant cell. Plants cells differ from animal cells in the following ways: they have a cell wall, chloroplasts, and they often contain a large central vacuole.

Figure 6a-5: Typical animal cell.

Internally, cells contain specialized structures known as organelles that carry out distinct cellular functions. Within these structures enzymes, a type of protein, are used to facilitate and regulate various chemical reactions. Table 6a-2 describes the function of a variety of cell structures including many organelles.

Table 6a-2: Description and function of common cell structures.

Structure	Description	Function
Cell Wall	Outer layer on a cell composed of cellulose or other complex carbohydrates.	Helps to support and protect the cell.
Plasma Membrane	A layer composed of lipids and proteins that controls the permeability of the cell to water and dissolved substances.	Regulates the movement of material into and out of the cell.
Flagellum (Flagella pl.)	Threadlike organelle that extends from the surface of the cell. Found in both prokaryotes and eukaryotes.	Used for movement of the cell or to move fluids over the cell's surface for absorption.
Pilus (Pili pl.)	Hollow, hairlike structures made of protein found on prokaryote cells.	Allows cell to attach itself to another cell.
Ribosomes	Tiny, complex structures composed of protein and RNA. Often attached to endoplasmic reticulum.	Ribosomes are involved in protein synthesis.
Endoplasmic Reticulum	Extensive system of internal membranes.	Forms compartments to isolate cell substances.
Nucleus	Double membrane structure that encases chromosomes.	Cell structure which directs protein synthesis and cell reproduction.
Chromosomes	Long strands of DNA.	Store hereditary information.
Nucleolus	Aggregations of rRNA and ribosomal proteins.	Area were ribosomes are manufactured.
Golgi Complex	Flattened stacks of membranes.	Used in the collection, packaging, and distribution of synthesized molecules.
Peroxisomes	Membrane confined spherical body about 0.2 to 0.5 micrometers in diameter.	Formed by the endoplasmic reticulum. Converts fats into carbohydrates. Detoxifies potentially harmful oxidants.
Lysosomes	Membrane confined spherical body about 0.2 to 0.5 micrometers in diameter.	Formed by the golgi complex. Contains digestive enzymes for braking down old cellular components.
Centrioles	Long hollow tubes composed of protein. Not found in plant cells.	Influence cell shape, move chromosomes during reproductive division, and are the internal structure for flagellum.
Secretory Vesicles	Membrane enclosed sack created at the golgi complex.	These structures contain cell secretions, like hormones and neurotransmitters. The secretory vesicles are then transported to the cell surface where they are release to the environment outside the cell.
Vacuole	Voids within the cytoplasm. Quite large in plant cells.	Used to store water and waste products.
Cytoplasm	Semifluid mixture that occupies most of the cell's interior. Contains sugars, amino acids, and proteins. Also, contains a protein fiber network.	Medium in which organelles and other internal structures exist in. Fiber network support the shape of the cell and anchor organelles to fixed positions.
Mitochondria	Elongated structures about 1 to 3 micrometers long. Resemble aerobic bacteria.	Structure which converts sugar into energy through oxidation.
Chloroplasts	Elongated structures with vesicles containing chlorophyll.	Site of photosynthesis.

Cells can also be classified according to how they obtain their energy. Some cells have the ability to use light or chemical energy found in the outside environment to manufacture their own sugars, fats, and proteins. We call these types of cells autotrophs. All 400,000 species of plants and a few species of bacteria use sunlight and the process of photosynthesis to obtain their energy. Some bacteria breakdown molecules found in the environment to release chemical energy to sustain their life. Organisms can also obtain their energy by consuming other organisms. These organisms are called heterotrophs. Heterotrophs include most types of bacteria and all of the animal and fungi species.

Some organisms consist of just one cell (bacteria, algae, and protozoa). However, most organisms are multi-cellular. Within multi-cellular organisms, groups of cells can become specialized to carry out a certain function. We call these functional groups of cells a tissue. An organ is a structure composed of several different types of tissues. Organs also have a specific structure and a particular function.

CITATION: Pidwirny, M. (2006). "Characteristics of Energy and Matter". Fundamentals of Physical Geography, 2nd Edition. 29/1/2012.

DESERT FACTS

noreply@blogger.com (Unknown) — Sat, 28 Jan 2012 11:07:00 +0000

A desert is an area of land that is marked by very sparse vegetation due to extreme climatic conditions and extremely low levels of precipitation. There are hot deserts as well as cold deserts. The Antarctic desert which spans across the continent of Antarctica is the most prominent example of a cold desert! Due to extremely low temperatures, vegetation and plant life is very sparse in these regions and the soil is ill suited for farming and cultivation. In hot deserts, the complete lack of moisture coupled with the extremely high temperatures make normal vegetation and cultivation of food items an impossible task. Only about 20% of the Earth's deserts are covered by sand. Based upon topography and region, there are precisely four types of deserts - Mountain-Basin deserts, Plateau Deserts, Regs and Intermontane Basins.

About one-third of the earth's land area is arid and semiarid--in total size, this is roughly equal to the combined areas of North and South America.
Dry lands are found in over 60 of the world's nations. There are 30 nations, many in the Middle East and Africa, that are at least 75% dry lands.
The world's largest area of dry lands is the Saharan-Arabian-Iranian-Thar Desert, which stretches some 6,000 miles from North Africa through the Middle East to northwest India.
Dry lands occur in the tropics and the midlatitudes. Tropical drylands occur from 15-35 degrees latitude and extend from west coasts into continental interiors. Mid latitude drylands occur from 35-55 degrees latitude and are concentrated in continental interiors.
Although vast stretches of desert are devoid of human settlement, the world's dry lands have been occupied and utilized by humans for tens of thousands of years.
North America's Sonoran Desert has the richest diversity of plants and animals of all the world's deserts, with more than 3000 plant species, many thousands of invertebrates (1200 different bee species alone!), and more than 550 vertebrate species (fish, reptiles, amphibians, mammals and birds).
Some desert rodents, like the "Kangaroo rats" (Dipodomys spp), that live in many North American dry lands, never have to drink water--they can metabolize all the water they need from the seeds that they eat.
Surprisingly, bees are much more abundant in deserts and savannas, both in terms of individuals and of species, than in wetter climates. The desert regions of northern Sonora (Mexico) and southern Arizona (USA), are thought to have more bee species (between 1,000 and 1,200) than any other region in the world.
Because deserts are too dry for many wood-decaying fungi to exist, termites play a crucial ecological role by eating, breaking down, and recycling cellulose (wood, grasses, cactus skeletons, and dung). Without termites, the entire desert ecosystem would collapse.
There are some 2,500 species of cactus in the world. With one possible exception, all are found naturally only in the Americas (North, Central, and South America, and the Caribbean).
The largest cactus in the world is the Cardon (Pachyserius pringlei), which dominates the deserts of Baja California and coastal Sonora, Mexico; Cardons can be up to 20 meters high and live for 200 years. They are closely related to Saguaro cactus (Carnegeia gigantea).
Cities now house almost half of the world's population, and megacities with more than 10 million population are increasing. (per AAAS Atlas of Population and Environment, atlas.aaas.org/ ). Roughly 800-900 million people in the world's dry lands live in cities. (per Philip Dobie, 2001, UNDP: Poverty and the Drylands).
Major dry land cities include Beijing (located in a dry subhumid zone of northern China); Mexico City, Mexico; Los Angeles, USA; Santiago, Chile; Madrid, Spain; Cairo, Egypt; Teheran, Iran.
The annual rainfall in deserts is less than 10 inches on an average.

SAHARA DESERT FACTS

Sahara Desert
Area:	9, 400, 000 km²
Continent Located In:	Africa
Countries It Covers:	Algeria, Chad, Libya, Egypt, Eritrea, Morocco, Mauritania, Mali, Niger, Sudan, Western Sahara and Tunisia

The Sahara is the world's largest hot desert, covering the maximum surface area among all other hot deserts! Antarctica is the world's largest cold desert
The Sahara desert covers the countries of Libya, Egypt, Algeria, Chad, Morocco, Mali, Sudan, Niger, Mauritania, Western Sahara and Tunisia.
Sahara desert plants include Welwitchsia, Peyote Cactus, date Palm, Thyme, etc. Sahara desert animals include, among others, sand vipers, monitor lizards, ostrich, death stalker scorpion, etc.
The Sahara started forming about 3 million years ago! The Sahara desert climate is pretty extreme with scorching hot days and chilly nights!
Prehistoric cave paintings in some Sahara desert regions depict it as a greener, more tropical region!
The Sahara desert is native to just about two million people, the reason of such low population being the extreme water scarcity as it receives just about 8 centimeters of rainfall each year!
Strange as it may sound, the peaks located in the Sahara get covered by snow in the winters!
The Sahara has a mostly rocky topography with different elevations at different places.
Some dunes in the Sahara are so high that they reach a height of about 180 meters!

GOBI DESERT FACTS

Gobi Desert
Area:	1, 295, 000 km² km²
Continent Located In:	Asia
Countries It Covers:	China, Inner Mongolia and 7 Mongolian Provinces (Govi-Altai, Sukhbaatar, Omnogovi, Dundgovi, Govisumber, Dornogovi and Bayankhongor)

Gobi desert is a cold desert! Very often, frost and snow can be seen on its dunes!
Gobi is not a primarily sandy desert; it is rocky having salt marshes and shifting sands on the lower regions.
Due to its location to the north of the Himalayan range, the rain bearing clouds are blocked by mountain range and the Gobi desert receives as little as only about 8 inches of rainfall every year.
The most common Gobi desert plants are drought resistant shrubs such as saltwort, sagebrush and grass.
There are about 33 different species of animal lives that exists in the Gobi. Most common Gobi desert animals are jerboa, golden eagle, Gobi bear, Asiatic wild ass, Asiatic ibex, wild camel, Bactrian camel, etc.
The first dinosaur eggs and some of the first paleontological fossils were discovered in the Gobi desert regions!

ATACAMA DESERT FACTS

Atacama Desert
Area:	1, 295, 000 km² km²
Continent Located In:	South America
Countries It Covers:	Argentina, Bolivia, Chile and Peru

The Atacama desert is located in the continent of South America. It is a 15 million years old cold desert!
The Atacama desert is flanked by the Andes Mountains on one side and the Chilean Coast Range on the other.
The Atacama desert witnesses quite a lot of human activities during the day as the pan American highway runs straight through it!
The Atacama is the world's largest reservoir of sodium nitrate!

Those were some brief but interesting desert facts. Despite being desolate and almost devoid of life and liveliness, deserts are some of the most interesting topographies to study. More so, because with the growing global warming due to increased ozone layer depletion, deserts are perhaps what the future of Earth has in store for the entire planet.

Courtesy: Ishani Chatterjee Shukla

GEOGRAPHY STANDARDS

noreply@blogger.com (Unknown) — Sun, 22 Jan 2012 09:47:00 +0000

Eighteen Standards That the Geographically Informed Person Knows and Understands

The World in Spatial Terms

1. How to use maps and other geographic representations, tools, and technologies to acquire, process, and report information.

2. How to use mental maps to organize information about people, places, and environments.

3. How to analyze the spatial organization of people, places, and environments on Earth's surface.

Places and Regions

4. The physical and human characteristics of places.

5. That people create regions to interpret Earth's complexity.

6. How culture and experience influence people's perception of places and regions.

Physical Systems

7. The physical processes that shape the patterns of Earth's surface.

8. The characteristics and spatial distribution of ecosystems on Earth's surface.

Human Systems

9. The characteristics, distribution, and migration of human populations on Earth's surface.

10. The characteristics, distributions, and complexity of Earth's cultural mosaics.

11. The patterns and networks of economic interdependence on Earth's surface.

12. The process, patterns, and functions of human settlement.

13. How forces of cooperation and conflict among people influence the division and control of Earth's surface.

Read more.......

CORAL REEF

noreply@blogger.com (Unknown) — Sat, 21 Jan 2012 17:04:00 +0000

Coral reefs are marine ridges or mounds, which have formed as a result of the deposition of calcium carbonate by living organisms, predominantly corals, but also a rich diversity of other organisms such as coralline algae and shellfish. Coral reefs provide a unique habitat characterised by high diversity and density of life. They occur globally in two distinct marine environments; deep, cold water (3-14°C) coral reefs, and shallow, warm water (21-30°C) coral reefs in tropical latitudes

Major coral reef sites are seen as red dots on this world map. Most of the reefs, with a few exceptions are found in tropical and semitropical waters, between 30° north and 30° south latitudes.

The condition of the growth of coral polyps.

1. High temperature- temperature above 20 degree Celsius.This is usually found in warm waters where the warm ocean current areas.

2. Clear shallow sea water- for the coral reef to survive well in seawater that is shallow and free from sediment. Coral need sunlight to grow , deep or muddy water is unsuitable.

3. Plentiful supply of oxygen and plankton- Coral need oxygen and plankton to grow. The part of the coast is washed by waves , currents and tides which maintain a fresh and plentiful supply of oxygen and plankton for the coral.

Types of coral reef

Fringing reefs

Reefs that are grow close to the coast. Most of the coral reefs in water of Singapore , Malaysia and Indonesia.

Barrier Reefs

Reefs that are situated further away from the coast in deeper water and are separated from the mainland by lagoons. The famous is Great Barrier Reef.

Atolls

are circular, oval, or horseshoe-shaped arrays of coral reef islands that are perched around an oceanic volcanic seamount and encircle a shallow central lagoon. The small islands are separated from each other by channels that lead from the sea into the central lagoon.

Distribution of Atolls

Because atoll formation requires coral reef building, atolls are limited to tropical waters. Atolls are most commonly found in the Pacific and Indian Oceans.

Size of Atolls

Atolls can vary greatly in size, ranging from quite small to over 130 kilometers (km) long and 32 km wide (Kwajalein in the Marshal Islands). The reef and lagoon area in some of the atolls of the Maldives are larger than 3000 km sq. Kiribati has a land area of about 390 km sq. Atoll islands are typically low lying, with elevations of less than 5 meters (m).

Atoll Development

COAST: Formation of Spits and Tombolos

noreply@blogger.com (Unknown) — Sat, 21 Jan 2012 15:52:00 +0000

A Spit is a long, narrow ridge of deposited materials that extends from the mainland into the sea. An example in Brunei is Muara Spit and Kuala Tutong Spit. When the spit is connected the island to the mainland to form a feature is called the Tombolos.

The long shore drift transports materials along the coast. If there is a sudden change in the direction of the coast, the longshore drift continues to transport the materials in the original direction to the deep sea. As the longshore drift enters the deep water, the materials are deposited. Over time, these materials accumulate above the water to form a spit. The spit continues to grow with the continuous deposition of materials. The spit join a nearby island to the mainland to form a tombolo.

Dungeness Spit, Washington. Olympic Mountains in background

Spit at Mission Bay, San Diego

COAST: Longshore Drift

noreply@blogger.com (Unknown) — Sat, 21 Jan 2012 15:34:00 +0000

Movement of material along a beach. When a wave breaks at an angle to the beach, pebbles are carried up the beach in the direction of the wave (swash). The wave returns to the sea at right angles to the beach (backwash) because that is the steepest gradient, carrying some pebbles with it. In this way, material moves in a zigzag fashion along a beach. Longshore drift is responsible for the erosion of beaches and the formation of spits (ridges of sand or shingle projecting into the water). Attempts are often made to halt longshore drift by erecting barriers, or groynes, at right angles to the shore.

Waves sometimes hit the beach at an angle. The incoming waves (swash) carry sand and shingle up onto the shore and the outgoing wave takes some material away with it. Gradually material is carried down the shoreline in the same direction as the longshore current.

Longshore drift carries sand and shingle up coastlines. Deposited material gradually builds up over time at headlands forming a new stretch of land called a spit. A spit that extends across a bay is known as a bar.

COAST: Wave Cut Platform

noreply@blogger.com (Unknown) — Sat, 21 Jan 2012 15:13:00 +0000

A wave-cut platform, or shore platform is the narrow flat area often found at the base of a sea cliff or along the shoreline of a lake, bay, or sea that was created by the action of waves. Wave-cut platforms are often most obvious at low tide when they become visible as huge areas of flat rock. Sometimes the landward side of the platform is covered by sand, forming the beach, and then the platform can only be identified at low tides or when storms move the sand.

FORMATION

It forms after destructive waves hit against the cliff face, causing undercutting between the high and low water marks, mainly as a result of corrasion and hydraulic power, creating a wave-cut notch. This notch then enlarges into a cave. The waves undermine this portion until the roof of the cave cannot hold due to the pressure and freeze-thaw weathering acting on it, and collapses, resulting in the cliff retreating landward. The base of the cave forms the wave-cut platform as attrition causes the collapsed material to be broken down into smaller pieces, while some cliff material may be washed into the sea. This may be deposited at the end of the platform, forming an off-shore terrace.

Because of the continual wave action, a wave-cut platform represents an extremely hostile environment and only the toughest of organisms can utilize such a niche.

The formation of wave cut platform

1. Original position of cliff

2. Cliff retreats

3. Present position of cliff

4. Sea level (high tide)

5. Wave cut notch at foot of cliffs

6. Wave cut platform

Wave-cut platform at Southerndown, South Wales

Wave-cut platforms from Lake Bonneville(Pleistocene), Utah.

VIDEO: Coastal Landforms

noreply@blogger.com (Unknown) — Sat, 21 Jan 2012 14:51:00 +0000

Cliff Slumping

Bays and Head Lands

Constructive waves

North Landing, Flamborough, The Holderness Coast

North Landing Arch, Flamborough, The Holderness Coast

North Landing, Flamborough, The Holderness Coast

Selwicks Bay (inc. stack), Flamborough, The Holderness Coast

COAST: Depositional Landforms

noreply@blogger.com (Unknown) — Sat, 21 Jan 2012 13:23:00 +0000

Coastal Deposition is when the sea drops or deposits material. This can include sand, sediment and shingle.

Beaches

The beach is the area between the lowest spring tide level and the point reached by the storm waves in the highest tides. Every beach is different but they are usually made up of material deposited on a wave-cut platform.

Spit

Longshore drift moves material along a coastline. Where there is an obstruction or the power of the waves is reduced the material is deposited. Where rivers or estuaries meet the sea deposition often occurs. The sediment which is deposited usually builds up over the years to form a long ridge of material (usually sand or shingle). Such a ridge is called a spit. Spurn Head on the Holderness Coast is an example of this feature.

MARSHES

Salt Marshes

A salt marsh is a coastal marsh that forms on mud flats. They usually form in very sheltered inlets and estuaries, or behind spits (places where fine sediment accumulates). Salt marshes form as vegetation builds up on these mud flats.

Sand Dunes

Sand dunes are created by strong winds and not by coastal erosion or deposition. As sand is blown up a beach is forms small hills. These are often rooted together by long-rooted grasses such as marram grass. Marram grass is usually planted to reduce the erosion of the otherwise unstable sand dunes.

COAST: Cliff Collapse

noreply@blogger.com (Unknown) — Sat, 21 Jan 2012 12:42:00 +0000

Cliff Recession

Rates of coastal erosion are determined by a range of factors. These include the fetch of a wave, type of beach, the supply of beach material by longshore drift, slope of the cliff, vegetation cover, local hydrology, the rate at which cliff debris are removed from the foot of the cliffs and the material that cliffs are made of. These are each examined below: .

fetch of the wave - the longer the fetch of the wave the greater the erosive energy of the wave
type of beach - beaches dissipate wave energy. The higher the beach the lower the energy in the wave as it meets the foot of the cliff (if it does at all!)
the supply of beach material by longshore drift - if there is a consistent supply of new beach material by longshore drift this will help preserve the beach. If this has been stopped, by building groynes for example, this can increase the rate of cliff recession as there is no beach material to absorb the energy of the waves.
vegetation cover - cliffs with vegetation cover tend to be less resistant to recession as roots help bind and reinforce the cliff material.
local hydrology - if there is a large amount of surface run off and infiltration this can increase the rate of cliff recession.
the rate at which debris are removed from the foot of cliffs - if material that has formed at the foot of cliffs is rapidly transported away then the cliffs will be quickly exposed to erosion.
cliff material - the material that cliffs are made of has a significant impact on cliff recession. Soft boulder clay cliffs recede much quicker than cliffs formed from sedimentary rock such as chalk. These types of cliff recede in quite different ways.

Soft Cliff Material

Cliffs formed from boulder clay, material deposited by glacial periods, are susceptible to high rates of coastal erosion. The Holderness Coast is an example of a coastline formed from boulder clay and is the fastest eroding coastline in Europe. The soft boulder clay is quickly eroded through hydraulic action and abrasion. However this is not the only way it is being eroded. Sub-aerial processes, such as rainfall, also cause erosion. This often happens where layers of boulder clay, left behind by melting glaciers, become saturated and cause the cliff to slump. The debris on the beach is then eroded by the sea leaving the cliff exposed once more.

Slumping explained:

Stage1 - the soft boulder clay holds rainwater and run-off.

Stage2 - Waves erode the base of the cliff creating a wave cut notch. The clay becomes saturated and forms a slip plane.

Stage 3 - The weight of the saturated cliff causes it to slump.

The video below shows evidence of slumping at Aldbrough. The video shows the early stages of the process. Water will percolate down the large crack to lubricate the slip plane. This will cause the land to slump further down.

Hard Cliff Material

In areas of more resistant cliff material erosion is greatest when waves break at the foot of a cliff. This causes erosion at the base of the cliff. This creates a wave-cut notch in the base of the cliff. As the notch increases in size the weight of the cliffs above become too much and the cliff collapses. This material will provide temporary protection for the cliff behind. However, once it has been removed by the sea this process will occur again. Where cliffs are made of more resistant material, wave cut platforms will be created.

COAST: Wave action

noreply@blogger.com (Unknown) — Sat, 21 Jan 2012 12:27:00 +0000

The size of a wave depends on its fetch. The fetch is the distance a wave travels. The greater the fetch, the larger the wave. Wind also has a significant effect on the size of waves. The stronger the wind the larger the wave. As a wave approaches a beach it slows. This is the result of friction between the water and the beach. This causes a wave to break.

There are two main types of wave. These are constructive and destructive waves. :

Constructive waves build beaches. Each wave is low. As the wave breaks it carries material up the beach in its swash. The beach material will then be deposited as the backwash soaks into the sand or slowly drains away. These waves are most common in summer.

Constructive Waves

Destructive waves destroy beaches. The waves are usually very high and very frequent. The back wash has less time to soak into the sand. As waves continue to hit the beach there is more running water to transport the material out to sea. these waves are most common in winter.

Erosional Landforms

Bays and headlands

Headlands form along coastlines in which bands of soft and hard rock outcrop at right angles to the coastline (see image below). Due to the different nature of the rock erosion occurs at different rates. Less resistant rock (e.g. boulder clay) erodes more rapidly than less resistant rock (e.g. chalk).

Bays and Headlands before Erosion

The image below shows the landforms that result from the different rates of erosion.

Bays and Headlands after erosion

Bays and Headlands

Erosion of a headland

A headland is an area of hard rock which sticks out into the sea. Headlands form in areas of alternating hard and soft rock. Where the soft rock erodes bays are formed either side of the headland. As the headland becomes more exposed to the wind and waves the rate of its erosion increases. When headlands erode they create distinct features such as caves, arches, stacks and stumps.

The diagram below shows the sequence in the erosion of a headland.

	Stage 1 Waves attack a weakness in the headland.
	Stage 2 A cave is formed.
	Stage 3 Eventually the cave erodes through the headland to form an arch.
	Stage 4 The roof of the arch collapses leaving a column of rock called a stack.
	Stage 5 The stack collapses leaving a stump.

THE EARTH'S RING OF FIRE

noreply@blogger.com (Unknown) — Fri, 20 Jan 2012 23:25:00 +0000

Circling the Pacific Basin, on the bottom of the sea bed, lie a dramatic series of volcanic arcs and oceanic trenches. The zone - the 'Ring of Fire' - notorious for frequent earthquakes and volcanic eruptions, coincides with the edges of one of the world's main tectonic plates. More than half of the world's active volcanoes above sea level are part of the ring.

Intense geological activity

In the past 25 years, scientists developed a theory called plate tectonics explaining the locations of volcanoes and other large-scale geologic features. According to tectonic theory, the surface of the Earth is made up of a patchwork of massive rigid plates, about 80km thick, which float in slow motion on top of the Earth's hot, pliable interior.

The plates change size and position over time, moving at speeds of between 1cm and 10cm every year - about the speed at which fingernails grow. New sea bed is constantly being created in the middles of the oceans - flowing out as hot lava, and rapidly cooling on contact with cold deep sea water. To make room for the continual addition of new ocean crust, all the earth's plates move. And as they move, intense geologic activity occurs at the plate edges. At the edges, one of three things may occur.

The plates can be moving away from each other, leaving space for new ocean floor.
Some plates are moving towards each other, causing one to submerge beneath the other.
Other boundaries slide past each other without much disturbance.

Tectonics and earthquakes

Parts of the plate boundary that slide past one another in opposite directions - such as the San Andreas Fault - cause minor earthquakes. The faults may also create cliffs or scarps thousands of feet high on the ocean bed. But where one oceanic plate collided with and is forced deep into the Earth's interior, the subsumed plate encounters high temperatures and pressures that partially melt solid rock. Some of this newly-formed magma rises to the Earth's surface and erupts, forming chains of violent volcanoes - like the Ring of Fire.

These narrow plate-boundary sites, known as subduction zones, are also associated with the formation of deep ocean trenches and big earthquakes. When there is an earthquake under the sea, one side of the ocean floor suddenly drops downward, beneath the top edge of the subducting plate. The resulting vertical fault will generate a tsunami - much as a wave machine in a swimming pool will generate one. The movements of the plates usually allow little warning for those at risk in coastal areas.

One warning of a tsunami is that there is a rush of water away from the coastline - but this predictor may mean the forthcoming seismic wave is only minutes away.

One week before Papua New Guinea's seismic activity, a large quake was recorded to the west of Western Samoa, and another took place in Vanuatu.

The frequency of Pacific quakes and seismic activity is not coincidence.

Courtesy: BBC News

VOLCANO

noreply@blogger.com (Unknown) — Fri, 20 Jan 2012 23:13:00 +0000

What is a volcano?

A volcano is a conical hill or mountain formed by material from the mantle being forced through an opening or vent in the Earth's crust.

What are the main features of a volcano?

What are active, dormant and extinct volcanoes?

Volcanoes are found in three states - extinct, dormant and active.

An extinct volcano will never erupt again.
A dormant volcano has not erupted in 2000 years.
An active volcano has erupted recently and is likely to erupt again

What are the different types of volcano?

There are a number of different types of volcanoes. The way they are formed depends on a number of factors e.g. the fluidity of the lava (how runny it is) and the temperature of the lava.

Composite

Composite volcanoes, sometimes known as strato volcanoes, are steep sided cones formed from layers of ash and lava flows. Composite volcanoes can rise over 8000 feet. Examples of composite volcanoes include Mount Fuji (Japan), Mount St Helens (USA) and Mount Pinatubo (Philippines).

A simple cross section through a composite volcano

When composite volcanoes erupt they are explosive and pose a threat to nearby life and property.

Shield

Shield volcanoes have gently sloping sides and are formed from layers of lava. Eruptions are typically non-explosive. Shield volcanoes produce fast flowing fluid lava that can flow for many miles. Examples of shield volcanoes include the Hawaiian volcanoes. Although these eruptions destroy property, death or injury to humans rarely occurs.

Dome (Acid Lava Cones)

Acid lava is much thicker than lava which flows from shield volcanoes. Dome volcanoes have much steeper sides than shield volcanoes. This is because the lava is thick and sticky. It cannot flow very far before It cools and hardens. An example is Puy de Dome in the Auvergne region of France which last erupted over 1 million years ago.

Where are volcanoes located?

Volcanoes are found along destructive (subducting) plate boundaries, constructive (divergent) plate boundaries and at hot spots in the earth's surface.

What is the Ring of Fire?

The 'Ring of Fire'is a volcanic chain surrounding the Pacific Ocean. It is formed along a destructive (subducting) plate boundary.

The Earth's Ring of Fire

What are lahars and pyroclastic flows?

The most destructive aspect of volcanoes are lahars and pyroclastic flows. Lahars are volcanic mudflows created when water (from rain or melt water from glaciers) and ash mix. This deadly combination can have devastating results on the surrounding area. When lahars settle they can be metres thick and as hard as cement. Lahars can occur long after a volcanic eruption. Pyroclastic flows are avalanches containing hot volcanic gases, ash and volcanic bombs. On steep volcanoes pyroclastic flows can reach speeds of over 100 miles per hour.

Why do people live close to volcanoes?

Volcanoes have a wide range of effects on humans. These can be problematic or beneficial. It is usually the destructive nature of volcanoes which is more widely documented. However, many people rely on volcanoes for their everyday survival. Today, many millions of people live close to volcanoes for this very reason.

People live close to volcanoes because Geothermal energy can be harnessed by using the steam from underground which has been heated by the Earth's magma. This steam is used to drive turbines in geothermal power stations to produce electricity for domestic and industrial use. Countries such as Iceland and New Zealand use this method of generating electricity.

Volcanoes attract millions of visitors around the world every year. Apart from the volcano itself, hot springs and geysers can also bring in the tourists. This creates many jobs for people in the tourism industry. This includes work in hotels, restaurants and gift shops. Often locals are also employed as tour guides.

Lava from deep within the earth contains minerals which can be mined once the lava has cooled. These include gold, silver, diamonds, copper and zinc, depending on their mineral composition. Often, mining towns develop around volcanoes.

Volcanic areas often contain some of the most mineral rich soils in the world. This is ideal for farming. Lava and material from pyroclastic flows are weathered to form nutrient rich soil which can be cultivated to produce healthy crops and rich harvests.