The+Lithosphere

=Mass movement info task - = = = = = = __** Soils **__ = = =

__** The Four Components of Soil **__

1. Water 2. Air 3 and 4 - Solid Material (organic and inorganic)



__** Characteristics of soils **__

Soils have a unique texture based on the particles making up the soil.

This also leads to the classification of soils based on how much sand, silt and clay is in the soil. As the diagram above shows the size of sand, silt and clay particles are different. A soil’s texture directly influences its nutrient content, moisture and drainage capacity. Clay soils tend to be fertile, but are often wet and poorly drained. Sandy soils drain easily but can be drought-prone and infertile. Loams retain moisture and are fertile and friable (crumbly and easy-to-work). Loam soil contains about 40 per cent sand, 40 per cent silt and 20 per cent clay, along with plenty of humus. Many plants tolerate a variety of soil textures, while some have more specific soil requirements.

Once the amount of sand, silt and clay in the soil is determined, a triangular graph like the one below can used to work out the type of soil.



The following test helps you assess the texture of your soil.
 * 1) Take a small handful of topsoil or subsoil and remove any gravel, stones, leaves and twigs. Break up any aggregates.
 * 2) Adding a drop of water at a time, knead the soil in your palms to make a small ball about 4 cm in diameter. Stop adding water as soon as the ball starts to stick to your hand, and knead for another 30 seconds. You will find it almost impossible to mould a ball with very sandy soil, and much easier with a clay soil.
 * 3) Press the ball between your fingers to determine its texture. A gritty feel indicates fine and coarse sand. (You can hear the sand grinding if you hold the ball to your ear.) A silky feel indicates silt, and a plastic, sticky feel indicates clay.
 * 4) You can also determine texture by making a soil ribbon. Press the ball between your thumb and forefinger. The longer the ribbon, the more clay is in your soil.



Soils also have a unique structure. Soil structure influences many important soil properties such as the rate of water infiltration, water retention, aeration, and drainage, because of its effects on pore size distribution. Good soil structure is important for plant growth in soils with clay and/or silt and is especially important in regions subject to management. Structural strength must be considered where stresses imposed at the soil surface may cause the structure to deteriorate. The stress may be imposed by cultivation, trampling by livestock, heavy traffic from logging, etc.



__** Soil forming processes **__

__**Eluviation**__ = The movement of humus, chemical substances, and mineral particles from the upper layers of a soil to lower layers by the downward movement of water through the soil profile. = =

__**Illuviation**__ = Deposition of humus, chemical substances, and fine mineral particles in the lower layers of a soil from upper layers because of the downward movement of water through the soil profile.

The movement of fine mineral particles down through the soil profile is often referred to as __**clay translocation**__.


 * Leaching** = the process in which water transports soil humus and inorganic nutrients in solution downwards in the soil profile or removes them completely in solution.

The diagram and photo below show how the downward movement of water in a soil. The minerals, organic material and clays are washed out from the upper layers of the soil (eluviation) leaving behind a bleached, pale coloured E horizon. The minerals, organic materials and clays are then deposited in the B horizon (illuviation) giving it a darker colour depending on the presence of organic material, iron and other minerals.





= __**Land Degradation, desertification and salinity**__ =


 * Nearly one-third of the earth is classed as arid or semi-arid desert.
 * An estimated six million hectares of productive land are lost every year because of desertification, land degradation and declining agricultural productivity.
 * More than 110 countries are affected by desertification.
 * Over 250 million people are directly affected by desertification and one billion people are at risk. These people include many of the world's poorest, most marginalised, and politically weak citizens.
 * The African continent is most affected by desertification. Two-thirds of the continent is desert or drylands, almost three-quarters of which are degraded to some degree.
 * Roughly 27 per cent of the China's land mass is desertified, with an average of 2,460 square kilometres of land being lost to advancing deserts each year. Nearly 400 million people live in these areas, and the economic loss to China has been estimated at around US$6.5 billion a year.
 * It is estimated that US$42 billion is lost worldwide each year through desertification.

Source: United Nations Convention to Combat Desertification @http://www.unccd.int/ __**What is desertification?**__ Desertification refers to both the spreading of current deserts and the degradation of land in areas of low rainfall. It is caused by both natural factors, such as drought, and human factors, such as overuse. A climate with large daily temperature variations, strong winds and intermittent but intense rainfall makes the fragile soils vulnerable to erosion and desertification. Increasing human demands lead to desertification through overcultivation, overgrazing, deforestation and poor water management. Grazing animals and firewood collection damage the vegetation holding soils together. Soil compacted by hard-footed animals is less able to soak up rain when it does fall and is easily eroded by the water and wind. Cutting trees for firewood leaves soil unshaded, leading to an increase in the temperature of the soil and in the rate of evaporation which draws salts to the surface. This further reduces plant growth. The high demands for the limited surface and ground water reserves leads to overuse and further salination.

__**What are the consequences of desertification?**__ The loss of soil fertility and vegetation cover and the decline of groundwater, which characterise desertification, lead to loss of biodiversity and productivity. This contributes to social, economic and political tensions. Lower yields from crops or grazing animals may lead to famine, poverty and conflict, forcing people to move away from their local area and lose their connection to the land and cultural traditions. Relocation can put pressure on other fragile environments and cause conflict and further relocation. Even people living further away are affected, as sandstorms cause respiratory problems and skin disorders. The blowing sand decreases visibility in cities and clogs rivers and water catchments. Desertification is both a cause and a consequence of poverty. Poorer and marginalised people are forced to farm fragile land, and seeking to make a living from it may cause further degradation.

= = = = __**Dryland Salinity**__

The diagram below shows that by changing the vegetation in the area from deep-rooted vegetation to shallow-rooted vegetation, there is more leakage of water into the groundwater store. This causes the water table (groundwater level full / saturated with water) to rise bringing dissolved salts to the surface. When the water input into the soil ceases and water is lost to evapotranspiration the water table drops below the surface leaving behind crystallised salts. Repeated raising and lowering of the water table after rain events, will lead to an increasing build up of salts on the surface rendering the land unproductive for farming.



The links below provide some good explanations of how dryland salinity occurs:

[|All about salinity] [|Salinity - our silent disaster] [|What causes dryland salinity?] [|How you recognise dryland salinity]

= __**Wetland Salinity**__ =

Wetland / Irrigated salinity is caused by irrigated water soaking through the soil and being added to existing underwater tables. This additional irrigated water causes the groundwater levels to rise. Each time the area is irrigated this salinity process is repeated. Vegetation damage, inhibited growth, bare or eroded soil, an increase in the growth of salt-tolerant plants, water logging on the ground’s surface, higher levels of salt in surface or groundwater and roads cracking or breaking up are the main problems for causing wetland salinity.



Irrigation is essential to feeding the world. Although only 17 percent of the world's cropland is irrigated, it produces over 33 percent of our food, making it roughly two and a half times as productive as rain-fed agriculture.
 * I**rrigation systems have existed for almost as long as settled agriculture. Five thousand years ago, the ancient Egyptians used the waters of the Nile to irrigate their crops. Two thousand years later, the great civilizations of the Fertile Crescent, stretching from the eastern Mediterranean to the Persian Gulf, were built on irrigated agriculture.

In spite of the pressing need for expansion, less new land is now being brought under irrigation than in the early 1970s. This is because of the shortage of suitable land, the rising cost of constructing irrigation systems and the scarcity of water itself. Bureaucratic interference, faulty management, lack of involvement of users, interrupted water supplies and poor construction have all led to poor performance, which has discouraged investment. In some cases up to 60 percent of the water withdrawn for use in irrigation never reaches the crops.

In addition, waterlogging and salinization have sapped the productivity of nearly 50 percent of the world's irrigated lands. Unless irrigated fields are properly drained, salts can build up in the soil, making the land infertile. Salinity affects 23 percent of China's irrigated land and 21 percent of Pakistan's. Other problems include the accumulation of pollutants and sediments in large dams and reservoirs, and the fact that irrigation systems provide an ideal habitat for the vectors of waterborne diseases.

The key to improved irrigation lies in more efficient use of water; recycling waste water and proper drainage. Drip irrigation and low-pressure spray systems are now being used in over 20 countries to deliver water directly to crops. Small dams, located closer to agricultural areas, are replacing large ones. Canals are being lined with concrete and covered to reduce seepage and evaporation. Several countries now use treated waste water for irrigation; Israel was using up to 30 percent of its urban waste water in this way as early as 1987.

FAO (Food and Agriculture Organisation) estimates that salt buildup has severely damaged about 30 million of the world's 237 million hectares of irrigated farmland. As much as 80 million hectares more are affected to some degree, with about 1.5 million hectares of irrigated land lost each year to waterlogging and salinity. (Source: FAO.org)

=** __Mass Movement__ **= = = __** Definition **__

Mass movement or mass wasting is movements of masses of bodies of soil, bed rock, rock debris, soil, or mud which usually occur along steep-sided hills and mountains because of the pull of gravity. This slipping of large amounts of rock and soil is seen in landslides, mud slides, and avalanches.

__**Classification of Mass Movemen**__ The classification of the different types of mass movement depends on: -
 * **Landslides** occur when masses of rock, earth, or debris move down a slope. They may be very small or very large, and can move at slow to very high speeds. However slow movement is also seen in the gradual downhill creep of soil on gently sloping land.
 * **Mudflows** (or debris flows) are rivers of rock, earth, and other debris saturated with water.
 * Rate of Movement - rapid or slow
 * Type of Movement - falling, sliding or flowing
 * Type of Material involved - rock, soil or debris

__**Causes of Mass Movement**__ Mass movements are caused by various conditions:
 * Volcanic activity many times causes huge mudflows when the icy cover of a volcano melts and mixes with the soil to form mud as the magma in the volcano stirs preceding an eruption.
 * Mudslides can also develop when water rapidly accumulates in the ground, such as during heavy rainfall or rapid snow melt, changing the earth into a flowing river of mud or "slurry.".
 * Earthquake shocks cause sections of mountains and hills to break off and slide down.
 * Human modification of the land or weathering and erosion help loosen large chunks of earth and start them sliding downhill.
 * Vibrations from machinery, traffic, weight loading from accumulation of snow; stockpiling of rock or ore; from waste piles and from buildings and other structures.
 * However, the trigger mechanism for mass movement is the gravitational pull of the earth on soil, rocks, and mud.