Geographic term

The Ring of Fire:
The "Ring of Fire" (map) is an arc stretching from New Zealand, along the eastern edge of Asia, north across the Aleutian Islands of Alaska, and south along the coast of North and South America. The Ring of Fire is composed over 75% of the world's active and dormant volcanoes.
This huge ring of volcanic and seismic (earthquake) activity was noticed and described before the invention of the theory of plate tectonics theory. We now know that the Ring of Fire is located at the borders of the Pacific Plate and other major tectonic plates.
Plates are like giant rafts of the earth's surface which often slide next to, collide with, and are forced underneath other plates. Around the Ring of Fire, the Pacific Plate is colliding with and sliding underneath other plates. This process is known as subduction and the volcanically and seismically active area nearby is known as a subduction zone. There is a tremendous amount of energy created by these plates and they easily melt rock into magma, which rises to the surface as lava and forms volcanoes.
Volcanoes are temporary features on the earth's surface and there are currently about 1500 active volcanoes in the world. About ten percent of these are located in the United States.
This is a listing of major volcanic areas in the Ring of Fire:
• In South America the Nazca plate is colliding with the South American plate. This has created the Andes and volcanoes such as Cotopaxi and Azul.
• In Central America, the tiny Cocos plate is crashing into the North American plate and is therefore responsible for the Mexican volcanoes of Popocatepetl and Paricutun (which rose up from a cornfield in 1943 and became a instant mountains).
• Between Northern California and British Columbia, the Pacific, Juan de Fuca, and Gorda plates have built the Cascades and the infamous Mount Saint Helens, which erupted in 1980.
• Alaska's Aleutian Islands are growing as the Pacific plate hits the North American plate. The deep Aleutian Trench has been created at the subduction zone with a maximum depth of 25,194 feet (7679 meters).
• From Russia's Kamchatka Peninsula to Japan, the subduction of the Pacific plate under the Eurasian plate is responsible for Japanese islands and volcanoes (such as Mt. Fuji).
• The final section of the Ring of Fire exists where the Indo-Australian plate subducts under the Pacific plate and has created volcanoes in the New Guinea and Micronesian areas. Near New Zealand, the Pacific Plate slides under the Indo-Australian plate.

Fig:1: Ring of Fire

Fig: 2: Ring Fire

Artesian Well:

A well drilled through impermeable strata to reach water capable of rising to the surface by internal hydrostatic pressure. (Engineering / General Engineering) a well sunk through impermeable strata into strata receiving water from an area at a higher altitude than that of the well, so that there is sufficient pressure to force water to flow upwards.

A deep well that passes through impermeable rock or sediment and reaches water that is held under pressure in a confined aquifer. In aquifers of this type, the water in the lower regions is trapped between two layers of impermeable rock and cannot rise to the level of the water table in the upper, unconfined regions. When a well penetrates the confined region, the pressure forces the water to rise within the well until it reaches the elevation of the water table in the unconfined region (a level known as the potentiometric surface).In a flowing artesian well the water is under enough pressure to rise all the way to the surface without being pumped and must be capped to control the flow.

Artesian well - a well drilled through impermeable strata into strata that receive water from a higher altitude so there is pressure to force the water to flow upward.

An artesian well is a deep well through which water is forced upward. The drill hits an aquifer, which is an underground water source. Rain water flows underground to this source. In South Dakota, the story of the artesian wells starts in the rocks of the Black Hills, which help the water flow into the ground. Underground the water spreads across the state. The first wells drilled into this source gushed up like oil wells. 

Fig:3: Artesian Well

Map Projection

Map Projections - types and distortion patterns

The shape of the Earth is represented as a sphere. It is also modeled more accurately as an oblate spheroid or an ellipsoid. A globe is a scaled down model of the Earth. Although they can represent size, shape, distance and directions of the Earth features with reasonable accuracy, globes are not practical or suitable for many applications. They are hard to transport and store; for example you cannot stuff a globe in your backpack while hiking or store it in your car’s glove compartment. Globes are not suitable for use at large scales, such as finding directions in a city or following a hiking route, where a more detailed image is essential. They are expensive to produce, especially in varying sizes (scales). On a curved surface, measuring terrain properties is difficult, and it is not possible to see large portions of the Earth at once.

Maps do not suffer from the above shortcomings and are more practical than globes in most applications. Historically cartographers have tried to address the challenge of representing the curved surface of the Earth on a map plane, and to this end have devised map projections. A map projection is the transformation of Earth’s curved surface (or a portion of) onto a two-dimensional flat surface by means of mathematical equations. During such transformation, the angular geographic coordinates (latitude, longitude) referencing positions on the surface of the Earth are converted to Cartesian coordinates (x, y) representing position of points on a flat map.

Types of map projections based on developable surface

One way of classifying map projections is by the type of the developable surface onto which the reference sphere is projected. A developable surface is a geometric shape that can be laid out into a flat surface without stretching or tearing. The three types of developable surfaces are cylinder, cone and plane, and their corresponding projections are called cylindrical, conical and planar. Projections can be further categorized based on their point(s) of contact (tangent or secant) with the reference surface of the Earth and their orientation (aspect).

Keep in mind that while some projections use a geometric process, in reality most projections use mathematical equations to transform the coordinates from a globe to a flat surface. The resulting map plane in most instances can be rolled around the globe in the form of cylinder, cone or placed to the side of the globe in the case of the plane. The developable surface serves as a good illustrative analogy of the process of flattening out a spherical object onto a plane.

Cylindrical projection

In cylindrical projections, the reference spherical surface is projected onto a cylinder wrapped around the globe. The cylinder is then cut lengthwise and unwrapped to form a flat map.

Tangent vs. secant cylindrical projection

Cylindrical projection - tangent and secant equatorial aspect © USGS

The cylinder may be either tangent or secant to the reference surface of the Earth. In the tangent case, the cylinder’s circumference touches the reference globe’s surface along a great circle (any circle having the same diameter as the sphere and thus dividing it into two equal halves). The diameter of the cylinder is equal to the diameter of the globe. The tangent line is the equator for the equatorial or normal aspect; while in the transverse aspect, the cylinder is tangent along a chosen meridian (i.e. central meridian).

In the secant case, the cylinder intersects the globe; that is the diameter of the cylinder is smaller than the globe’s. At the place where the cylinder cuts through the globe two secant lines are formed.

The tangent and secant lines are important since scale is constant along these lines (equals that of the globe), and therefore there is no distortion (scale factor = 1). Such lines of true scale are called standard lines. These are lines of equidistance. Distortion increases by moving away from standard lines.

In normal aspect of cylindrical projection, the secant or standard lines are along two parallels of latitude equally spaced from equator, and are called standard parallels. In transverse aspect, the two standard lines run north-south parallel to meridians. Secant case provides a more even distribution of distortion throughout the map. Features appear smaller between secant lines (scale < 1) and appear larger outside these lines (scale > 1).

Cylindrical aspect – equatorial (normal), transverse, oblique

Cylindrical projection - transverse and oblique aspect © USGS

The aspect of the map projection refers to the orientation of the developable surface relative to the reference globe. The graticule layout is affected by the choice of the aspect.

In normal or equatorial aspect, the cylinder is oriented (lengthwise) parallel to the Earth’s polar axis with its center located along the equator (tangent or secant). The meridians are vertical and equally spaced; the parallels of latitude are horizontal straight lines parallel to the equator with their spacing increasing toward the poles. Therefore the distortion increases towards the poles. Meridians and parallels are perpendicular to each other. The meridian that lies along the projection center is called the central meridian.

In transverse aspect, the cylinder is oriented perpendicular to the Earth’s axis with its center located on a chosen meridian (a line going through the poles). And the oblique aspect refers to the cylinder being centered along a great circle between the equator and the meridians with its orientation at an angle greater than 0 and less than 90 degrees relative to the Earth’s axis.

Examples of cylindrical projections include Mercator, Transverse Mercator,Oblique Mercator, Plate Carré, Miller Cylindrical, Cylindrical equal-area, Gall–Peters, Hobo–Dyer, Behrmann, and Lambert Cylindrical Equal-Area projections.

Conical (conic) projection

In conical or conic projections, the reference spherical surface is projected onto a cone placed over the globe. The cone is cut lengthwise and unwrapped to form a flat map.

Tangent vs. secant conical projection

Conic projection - tangent and secant © USGS

The cone may be either tangent to the reference surface along a small circle (any circle on the globe with a diameter less than the sphere’s diameter) or it may cut through the globe and be secant (intersect) at two small circles.

For the polar or normal aspect, the cone is tangent along a parallel of latitude or is secant at two parallels. These parallels are called standard parallels. This aspect produces a map with meridians radiating out as straight lines from the cone’s apex, and parallels drawn as concentric arcs perpendicular to meridians.

Scale is true (scale factor = 1) and there is no distortion along standard parallels. Distortion increases by moving away from standard parallels. Features appear smaller between secant parallels and appear larger outside these parallels. Secant projections lead to less overall map distortion.

Conical aspect – equatorial (normal), transverse, oblique

The polar aspect is the normal aspect of the conic projection. In this aspect the cone’s apex is situated along the polar axis of the Earth, and the cone is tangent along a single parallel of latitude or secant at two parallels. The cone can be situated over the North or South Pole. The polar conic projections are most suitable for maps of mid-latitude (temperate zones) regions with an east-west orientation such as the United States.

In transverse aspect of conical projections, the axis of the cone is along a line through the equatorial plane (perpendicular to Earth’s polar axis).Oblique aspect has an orientation between transverse and polar aspects. Transverse and oblique aspects are seldom used.

Examples of conic projections include Lambert Conformal Conic, Albers Equal Area Conic, and Equidistant Conic projections.

Planar projection – Zenithal

In planar (also known as Zenithal or zenithal) projections, the reference spherical surface is projected onto a plane.

Tangent vs. secant planar projection

Planar (Zenithal) projection - tangent and secant © USGS

The plane in planar projections may be tangent to the globe at a single point or may be secant. In the secant case the plane intersects the globe along a small circle forming astandard parallel which has true scale. The normal polar aspect yields parallels as concentric circles, and meridians projecting as straight lines from the center of the map. The distortion is minimal around the point of tangency in the tangent case, and close to the standard parallel in the secant case.

Planar aspect – polar (normal), transverse (equatorial), oblique

The polar aspect is the normal aspect of the planar projection. The plane is tangent to North or South Pole at a single point or is secant along a parallel of latitude (standard parallel). The polar aspect yields parallels of latitude as concentric circles around the center of the map, and meridians projecting as straight lines from this center. Zenithal projections are used often for mapping Polar Regions, the polar aspect of these projections are also referred to as polar Zenithal projections.

In transverse aspect of planar projections, the plane is oriented perpendicular to the equatorial plane. And for the oblique aspect, the plane surface has an orientation between polar and transverse aspects.

These projections are named Zenithal due to the fact that they preserve direction property from the center point of the projection. Great circles passing through the center point are drawn as straight lines.

Examples of Zenithal projections include: Zenithal Equidistant, Lambert Zenithal Equal-Area, Gnomonic, Stereographic, and Orthographicprojections.

Zenithal Perspective Projections

Some classic Zenithal projections are perspective projections and can be produced geometrically. They can be visualized as projection of points on the sphere to the plane by shining rays of light from a light source (or point of perspective). Three projections, namely gnomonic, stereographic and orthographic can be defined based on the location of the perspective point or the light source.

Gnomonic Projection (also known as Central or Gnomic Projection)

Gnomonic Projection © USGS

The point of perspective or the light source is located at the center of the globe in gnomonic projections. Great circles are the shortest distance between two points on the surface of the sphere (known as great circle route). Gnomonic projections map all great circles as straight lines, and such property makes these projections suitable for use in navigation charts. Distance and shape distortion increase sharply by moving away from the center of the projection.

Stereographic Projection

Stereographic projection © USGS

In stereographic projections, the perspective point is located on the surface of globe directly opposite from the point of tangency of the plane. Points close to center point show great distortion on the map. Stereographic projection is a conformal projection, that is over small areas angles and therefore shapes are preserved. It is often used for mapping Polar Regions (with the source located at the opposite pole).

Orthographic Projection

Orthographic projection © USGS

In orthographic projections, the point of perspective is at infinite distance on the opposite direction from the point of tangency. The light rays travel as parallel lines. The resulting map from this projection looks like a globe (similar to seeing Earth from deep space). There is great distortion towards the borders of the map.

Map projection types based on distortion characteristics

As stated above spherical bodies such as globes can represent size, shape, distance and directions of the Earth features with reasonable accuracy. It is impossible to flatten any spherical surface (e.g. an orange peel) onto a flat surface without some stretching, tearing, or shearing. Similarly, when trying to project a spherical surface of the Earth onto a map plane, the curved surface will get deformed, causing distortions in shape (angle), area, direction or distance of features. All projections cause distortions in varying degrees; there is no one perfect projection preserving all of the above properties, rather each projection is a compromise best suited for a particular purpose.

Different projections are developed for different purposes. Some projections minimize distortion or preserve some properties at the expense of increasing distortion of others. The choice of a projection for a map depends on such factors as the purpose for which the map will be used, the area being mapped, and the map’s scale (distortion is more pronounced in small-scale mapping).

Measuring map scale distortion – scale factor & principal (nominal) scale

As mentioned above, a reference globe (reference surface of the Earth) is a scaled down model of the Earth. This scale can be measured as the ratio of distance on the globe to the corresponding distance on the Earth. Throughout the globe this scale is constant. For example, a 1:250000 representative fraction scale indicates that 1 unit (e.g. km) on the globe represents 250000 units on Earth. The principal scale or nominal scale of a flat map (the stated map scale) refers to this scale of its generating globe.

However the projection of the curved surface on the plane and the resulting distortions from the deformation of the surface will result in variation of scale throughout a flat map. In other words the actual map scale is different for different locations on the map plane and it is impossible to have a constant scale throughout the map. This variation of scale can be visualized by Tissot's indicatrix explained in detail below. Measure of scale distortion on map plane can also be quantified by the use of scale factor.

Scale factor is the ratio of actual scale at a location on map to the principal (nominal) map scale (SF = actual scale / nominal scale). This can be alternatively stated as ratio of distance on the map to the corresponding distance on the reference globe. A scale factor of 1 indicates actual scale is equal to nominal scale, or no scale distortion at that point on the map. Scale factors of less than or greater than one are indicative of scale distortion. The actual scale at a point on map can be obtained by multiplying the nominal map scale by the scale factor.

As an example, the actual scale at a given point on map with scale factor of 0.99860 at the point and nominal map scale of 1:50000 is equal to (1:50000 x 0.99860) = (0.99860 / 50000) = 1:50070 (which is a smaller scale than the nominal map scale). Scale factor of 2 indicates that the actual map scale is twice the nominal scale; if the nominal scale is 1:4million, then the map scale at the point would be (1:4million x 2) = 1:2million. A scale factor of 0.99950 at a given location on the map indicates that 999.5 meters on the map represents 1000 meters on the reference globe.

As mentioned above, there is no distortion along standard lines as evident in following figures. On a tangent surface to the reference globe, there is no scale distortion at the point (or along the line) of tangency and therefore scale factor is 1. Distortion increases with distance from the point (or line) of tangency.

Map scale distortion of a tangent cylindrical projection - SF = 1 along line of tangency

Scale distortion on a tangent surface to the globe

On a secant surface to the reference globe, there is no distortion along the standard lines (lines of intersection) where SF = 1. Between the secant lines where the surface is inside the globe, features appear smaller than in reality and scale factor is less than 1. At places on map where the surface is outside the globe, features appear larger than in reality and scale factor is greater than 1. A map derived from a secant projection surface has less overall distortion than a map from a tangent surface.

Map scale distortion of a secant cylindrical projection - SF = 1 along secant lines

Scale distortion on a secant surface to the globe

Tissot's indicatrix – visualizing map distortion pattern

A common method of classification of map projections is according to distortion characteristics - identifying properties that are preserved or distorted by a projection. The distortion pattern of a projection can be visualized by distortion ellipses, which are known as Tissot's indicatrices. Each indicatrix (ellipse) represents the distortion at the point it is centered on. The two axes of the ellipse indicate the directions along which the scale is maximal and minimal at that point on the map. Since scale distortion varies across the map, distortion ellipses are drawn on the projected map in an array of regular intervals to show the spatial distortion pattern across the map. The ellipses are usually centered at the intersection of meridians and parallels. Their shape represents the distortion of an imaginary circle on the spherical surface after being projected on the map plane. The size, shape and orientation of the ellipses are changed as the result of projection. Circular shapes of the same size indicate preservation of properties with no distortion occurring.

Equal Area Projection – Equivalent or Authalic

Gall-Peters cylindrical equal-area projection Tissot's indicatrix

© Eric Gaba – Wikimedia Commons user: Sting

Equal area map projections (also known as equivalent or authalic projection) represent areas correctly on the map. The areas of features on the map are proportional to their areas on the reference surface of Earth. Maintaining relative areas of features causes distortion in their shapes, which is more pronounced in small-scale maps.

The shapes of the Tissot’s ellipses in this world map Gall-Peters cylindrical equal-area projection are distorted; however each of them occupies the same amount of area. Along the standard parallel lines in this map (45° N and 45°S), there is no scale distortion and therefore the ellipses would be circular.

Equal area projections are useful where relative size and area accuracy of map features is important (such as displaying countries / continents in world maps), as well as for showing spatial distributions and general thematic mapping such as population, soil and geological maps. Some examples are Albers Equal-Area Conic, Cylindrical Equal Area,Sinusoidal Equal Area, and Lambert Zenithal Equal Area projections.

Conformal Projection – Orthomorphic or Autogonal

Mercator - conformal projection Tissot's indicatrix

© Eric Gaba – Wikimedia Commons user: Sting

In conformal map projections (also known as orthomorphic or autogonal projection) local angles are preserved; that is angles about every point on the projected map are the same as the angles around the point on the curved reference surface. Similarly constant local scale is maintained in every direction around a point. Therefore shapes are represented accurately and without distortion for small areas. However shapes of large areas do get distorted. Meridians and parallels intersect at right angles. As a result of preserving angles and shapes, area or size of features are distorted in these maps. No map can be both conformal and equal area.

Tissot’s indicatrices are all circular (shape preserved) in this world mapMercator projection, however they vary in size (area distorted). Here the area distortion is more pronounced as we move towards the poles. A classic example of area exaggeration is the comparison of land masses on the map, where for example Greenland appears bigger than South America and comparable in size to Africa, while in reality it is about one-eight the size of S. America and one-fourteenth the size of Africa. A feature that has made Mercator projection especially suited for nautical maps and navigation is the representation of rhumb line or loxodrome (line that crosses meridians at the same angle) as a straight line on the map. A straight line drawn on the Mercator map represents an accurate compass bearing.

Preservation of angles makes conformal map projections suitable for navigation charts, weather maps, topographic mapping, and large scale surveying. Examples of common conformal projections include Lambert Conformal Conic, Mercator, Transverse Mercator, and Stereographic projection.

Equidistant Projection

Equirectangular (equidistant cylindrical) projection Tissot's indicatrix

© Eric Gaba – Wikimedia Commons user: Sting

In equidistant map projections, accurate distances (constant scale) are maintained only between one or two points to every other point on the map. Also in most projections there are one or more standard lines along which scale remains constant (true scale). Distances measured along these lines are proportional to the same distance measurement on the curved reference surface. Similarly if a projection is centered on a point, distances to every other point from the center point remain accurate. Equidistant projections are neither conformal nor equal-area, but rather a compromise between them.

In this world map equidistant cylindrical projection (also known as plate carrée), Tissot’s ellipses are distorted in size and shape. However while there are changes in the ellipses, their north-south axis has remained equal in length. This indicates that any line joining north and south poles (meridian) is true to scale and therefore distances are accurate along these lines. Plate carrée is a case of equirectangular projection with Equator being a standard parallel.

Equidistant projections are used in air and sea navigation charts, as well as radio and seismic mapping. They are also used in atlases and thematic mapping. Examples of equidistant projections are Zenithal equidistant, equidistant conic, and equirectangular projections.

True-Direction Projection – Zenithal or Zenithal

Gnomonic projection © Wikimedia Commons

Directions from a central point to all other points are maintained accurately in Zenithal projections (also known as zenithal or true-direction projections). These projections can also be equal area, conformal or equidistant.

The gnomonic map projection in the image is centered on the North Pole with meridians radiating out as straight lines. In gnomonic maps great circles are displayed as straight lines. Directions are true from the center point (North Pole).

True-direction projections are used in applications where maintaining directional relationships are important, such as aeronautical and sea navigation charts. Examples include Lambert Zenithal Equal-Area, Gnomonic, and Zenithal equidistant projections.

Compromise Projections

Robinson projection © Eric Gaba – Wikimedia Commons user: Sting

Some projections do not preserve any of the properties of the reference surface of the Earth; however they try to balance out distortions in area, shape, distant, and direction (thus the name compromise), so that no property is grossly distorted throughout the map and the overall view is improved. They are used in thematic mapping. Examples includeRobinson projection and Winkel Tripel projection.

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How soil is erosioned

3. Soil Erosion

3.1 Overview of processes

3.2 Water Erosion

3.3 Wind Erosion

3.1 Overview of processes

Soil erosion is the detachment and transportation of soil particles by the forces of water and/or wind.  It is a process that transforms soil into sediment. Sediment consists of transported and deposited particles or aggregates derived from rock, soil, or biological material.

3.1.1 Geologic vs. Accelerated Soil Erosion

Geological erosion is a natural process that wears down topographic highs (hills and mountains) and fills in topographic lows (valleys, lakes, and bays) through the deposition of eroded sediments.

3) Dissolution (or solution) water is capable of dissolving

Erosion that exceeds normal geologic erosion becomes destructive and is called accelerated erosion.  This type of erosion occurs when the soil and natural vegetation are disturbed by human activity.  Accelerated erosion is often 10 to 1000 times as destructive as geological erosion.

3.1.2 Soils Susceptible to Erosion

Soils that are susceptible to erosion include:

·         soils with low water infiltration capability

·         soils with low organic matter content

·         soils with poor (unstable) structure

·         soils on steep hills (especially in regions of high rainfall)

·         soils with hydrophobic characteristics (usually intensified by fire)

3.1.3 Effects/Consequences of Soil Erosion

Soil erosion causes two main problems: 

·         Loss of soil productivity: When topsoil erodes, the less fertile and harder B horizon becomes exposed.  This leads to lower forage production, lower water infiltration and greater runoff.

• Sediment pollution: when eroded sediment is rich in fertilizers or pesticides, it can upset the ecosystem at its point of deposition.  In addition, sediments may damage machinery, agitate respiratory problems and reduce visibility.

3.2 Water Erosion

3.2.1 Mechanism:

There are three steps to accelerated erosion by water:

1)    Detachment or loosening of soil particles caused by flowing water, freezing and thawing of the topsoil, and/or the impact of falling raindrops.

2)    Transportation of soil particles by floating, rolling, dragging, and/or splashing.

3)    Deposition of transported particles at some place lower in elevation.

Mechanics: detachment, transportation, deposition

The three-step process of soil erosion by water starts with the impact of raindrops on soil.

Susceptibility to wind erosion is related to the following soil properties:

• water content
• stability of dry soil aggregates
• stability of soil crust
• surface roughness
• vegetative and/or mulch cover

Soil profile - a vertical section of soil from the ground surface to the parent rock

Profile - a vertical section of the Earth's crust showing the different horizons or layers. If there is no compaction present, the topsoil will present a crumbly face throughout the topsoil profile and, in this condition, every part of the soil profile can be accessed by the plant roots. It also helps draw nutrients into the upper regions of the soil profile where cash crops can use them the next season.

Definition of soil profile: The vertical section of the soil showing the various layers from the surface to the unaffected parent material is known as a soil profile.

Master horizons and sub horizons

O horizon: It is called as organic horizon. It is formed in the upper part of the mineral soil, dominated by fresh or partly decomposed organic materials.

• This horizon contains more than 30% organic matter if mineral fraction has more than 50 % clay (or) more than 20 % organic matter if mineral fraction has less clay.
• The organic horizons are commonly seen in forest areas and generally absent in grassland, cultivated soils.
• O1 - Organic horizon in which the original forms of the plant and animal residues can be recognized through naked eye.
• O2 - Organic horizon in which the original plant or animal matter cannot be recognized through naked eye.
• A horizon - Horizon of organic matter accumulation adjacent to surface and that has lost clay, iron and Aluminum.
• A1 - Top most mineral horizon formed adjacent to the surface. There will be accumulation of humified organic matter associated with mineral fraction and darker in Color than that of lower horizons due to organic matter.
• A2 - Horizon of maximum eluviation of clay, iron and aluminium oxides and organic matter. Loss of these constituents generally results in accumulation of quartz and other sand and silt size resistant minerals. Generally lighter in Colour than horizons above and below.
• A3 - A transitional layer between A and B horizons with more dominated properties of A1 or A2 above than the underlying B horizon. This horizon is sometimes absent. Solum.
• B horizon - Horizon in which the dominant features are accumulation of clay, iron, aluminium or humus alone or in combination. Coating of sesquioxides will impart darker, stronger of red Colour than overlying or underlying horizons.
• B1 - A transitional layer between A and B. More like A than B.
• B2 - Zone of maximum accumulation of clay, iron and aluminium oxide that may have moved down from upper horizons or may have formed in situ. The organic matter content is generally higher and Colour darker than that of A2 horizon above.
• B3 - Transitional horizon between B and C and with properties more similar to that of overlying B2 than underlying C.
• C horizon - It is the horizon below the solum (A + B), relatively less affected by soil forming processes. It is outside the zone of major biological activity. It may contain accumulation of carbonates or sulphates, calcium and magnesium
• R - Underlying consolidated bed rock and it may or may not be like the parent rock from which the slump is formed.

3.3 Wind Erosion

3.3.1 Mechanics       

·         Wind erosion occurs where soil is exposed to the dislodging force of wind.  The intensity of wind erosion  varies with surface roughness, slope, type of cover on the soil surface, and wind velocity, duration, and angle of incidence.  Fine soil particles can be carried to great heights and for hundreds of kilometers.

Susceptibility to wind erosion is related to the following soil properties:

•           Water content

•           Stability of dry soil aggregates

•           Stability of soil crust

•           Surface roughness

•           Vegetative and/or mulch cover