WEATHERING Weathering is the gradual destruction of rock under surface conditions. Weathering may involve physical processes (mechanical weathering)

WEATHERING

Weathering is the gradual destruction of rock under surface conditions. Weathering may involve physical processes (mechanical weathering) or chemical activity (chemical weathering). Some workers also include the actions of living things (organic weathering), although these can also be classified as mechanical or chemical or a combination of both.

As stated earlier mechanical weathering involves the breaking down of rocks due to a kind of pressure exerted on the rock, which can be due to various reasons. The primary method of mechanical weathering is the alteration in size that the particle would go through and it would definitely get smaller with weathering..

Mechanical Weathering

Types of Mechanical Weathering

1.Ice Wedging= Expansion of H2O and pushes the cracks wider apart.

2.Sheeting= series of fracture due to expansion of rock as a result of removal of overlying material.

Chemical WeatheringChemical weathering takes place in almost all types of rocks. Smaller rocks are more susceptible, however, because they have a greater amount of surface area.Chemical reactions break down the bonds holding the rocks together, causing them to fall apart, forming smaller and smaller pieces. Chemical weathering is much more common in locations where there is a lot of water. This is because water is important to many of the chemical reactions that can take place. Warmer temperatures are also more friendly to chemical weathering. The most common types of chemical weathering are oxidation, hydrolysis and carbonation.

Chemical Weathering

types of Chemical Weathering:

1.Oxidations= oxygen reacts with H2O iron in mineral forming.2.Carbonation= Co2+ rainH2O – Carbonic Acid+ mineral. 3.Hydration= mineral+ H2O ( expand)4.Dissolution= mineral dissolved in H2O

RATES OF WEATHERING

The speed at which a rock weathers will depend on the following:

1.The type and hardness of the minerals in the rock2.The type of rock3.The climate

MASS WASTING

defined as the down slope movement of material under the direct influence of gravity.   Most types of mass wasting are aided by weathering and usually involve sacrificial (surface) materials.  The material moves at rates ranging from almost imperceptible, as in the case of creep, to extremely fast as in a rock fall or slide.  Though water can play an important role, the relentless pull of gravity is the major force behind mass wasting.

TWO TYPE SOF MASS WASTING

1. ROCK SLIDE -- The usually rapid downward movement of newly detached segments of bedrock. The rock mass that has reached its current position through such a movement.

2. LAND SLIDE--or landslip is a geological phenomenon which includes a wide range of ground movement, such as rockfalls, deep failure of slopes and shallow  debrisdebris flows, which can occur in offshore, coastal and onshore environments.

SOIL

Soil refers to the precious mixture of weathered rock fragments, minerals grains, organic debris, and moisture .

ESOIL PROFILE

Soil Profile refers to the layers of soil; horizon A, B, and C. If you're wondering what horizon A is, here's your answer: The litter horizon A refers to the upper layer of soil, nearest the surface. It is commonly known as topsoil. In the woods or other areas that have not been plowed or tilled, this layer would probably include organic litter, such as fallen leaves and twigs .helps prevent erosion, holds moisture, and decays to form a very rich soil known as humus. Horizon A provides plants with nutrients they need for a great life.

What affects soil formation?

Soil characteristics develop as a result of their origin and environment. Soil begins as a particular rock material and develops slowly over many years. Each soil is a product of a combination of the following factors. What affects soil formation?

Parent material

Climate

Living organisms (biota)

Topography

Time

Parent Material

Alluvium – finely pulverized rock laid down by running water. Mostly silt and clay particles with some sand.

Marine Deposits – finely pulverized rock laid down under sea. This material has been thrust up by shifts in the earth’s crust.

Loess – salty, floury material laid down by winds. Mostly silt and clay with little or no sand.

Physical weathering – results from mechanical agents, such as heating & cooling, freezing & thawing, &/or abrasion.

•Materials are still the same at the molecular level.

•Materials are classified by the way they have been moved or scattered

Climate

Topography

Topography refers to the “lay of the land” or the angle & length of the slope.It affects soil formation because it influences runoff, drainage, & erosion.It also may affect the type & amount of plant growth (biggest factor in determining type & amount of organic matter)

As soon as material has become loose enough to hold enough water, air, and nutrients for plant growth, it is considered a soil.

Soil formation/development may take place over several centuries or just a few days.

SOIL EROSION

The denudation of the soil cover and

subsequent washing down is described as soil

erosion. The processes of soil formation and

erosion, go on simultaneously and generally

there is a balance between the two. Sometimes,

this balance is disturbed due to human activities

like deforestation, over-grazing, construction and

mining etc., while natural forces like wind,

glacier and water lead to soil erosion.

What Causes Soil Erosion?There is no particular soil erosion cause which can be singled out and assumed as the main cause of soil erosion. The process has many underlying factors, some induced by nature and some by humans.Human Induced Causes of Soil ErosionHuman exploitation of nature is perhaps the most hazardous cause of soil erosion, which has increased over the last decade. Human activities, such as faulty farming systems, deforestation caused by overgrazing, clearance of land for agricultural purposes and construction, dam construction and diversion of the natural course of river, and mining activities are just a few among the various human activities which have either directly or indirectly weakened the topmost layer of the planet, thus making it vulnerable to excessive wearing away by the various agents of erosion. For instance, tree roots help in holding the soil together, and therefore depletion of vegetation cover is bound to make soil vulnerable to erosion by running water.

The Effects of Soil ErosionSoil erosion occurs when wind and

water strips the soil from a given area faster than it can form. Most of the time, soil erosion occurs as a result of man-made issues, such as overgrazing farmland or the use of unsuitable fertilizers. The effects of erosion can be felt both on the site where the erosion takes place and at off-site locations.