Wearing Down Landforms

Transcription

1 Wearing Down Landforms

2 Denudation Denudation has also been called gradation. It is the Natural loss of soil and rock debris, blown away by wind or washed away by running water, laying bare the rock below. Over millions of years, denudation causes a general lowering of the landscape.

3 Denudation involves two types of processes Weathering refers to processes that physically breakdown and chemically alter earth material. Erosion is the displacement or transportation of solids (soil, mud, rock, and so forth) by the agents of wind, water, ice, or movement in response to gravity. Although the processes may be simultaneous, erosion is to be distinguished from weathering, which is the decomposition of rock.

4 Weathering There are two types of weathering 1. Physical weathering, also known as mechanical weathering, is the breakdown of large pieces of earth material into smaller ones. Think of physical weathering as the disintegration of rock without changing its chemical composition.

5 Physical or Mechanical weathering takes place when rocks are broken down without any change in the chemical nature of the rocks. The rocks are essentially torn apart by physical force, rather than by chemical breakdown.

6 Physical Weathering

7 Frost Fracture Freeze-thaw action, sometimes known as ice crystal growth or frost shattering, occurs when water in cracks and joints of rocks freeze and expand.

8 This pressure is often higher than the resistance of most rocks and causes the rock to shatter. This happens in climates where the temperature fluctuates above and below the freezing point.

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10 Temperature Variation minerals in rocks expand and contract in climates where temperature ranges are extreme, like in glacial regions of the world, or when exposed to extreme heat, like during a forest fire. Crystal structures of minerals become stressed during contraction and expansion and the mineral crystals separate.

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12 Exfoliation Some types of rocks, such as coarse grained igneous rocks, weather by breaking along curved surfaces, causing the rock to break apart in rounded sheets like the layer of an onion.

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14 Other forms of physical weathering Plant growth can also cause physical weathering.

15 Burrowing animals contribute by expanding existing cracks and fractures in rocks as they tunnel through them.

16 Chemical Weathering The decomposition of rock by the chemical breakdown of minerals. Results in a change in rock composition; typically replacing strong minerals with weaker minerals, thus hastening the break down of the rock. The three common chemical reactions associated with chemical weathering are solution, hydrolysis, and oxidation. The main agent of chemical weathering = water

17 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.

18 The three common chemical reactions associated with chemical weathering are solution, hydrolysis, and oxidation. The main agent of chemical weathering = water

19 Solution/dissolution Solution occurs when rocks and/or minerals are dissolved by water. The dissolved material is transported away leaving a space in the rock. One consequence of this process is the formation of caves in limestone areas. Usually involves acidic rainwater

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22 Hydrolysis Also involves the carrying away of minerals in solution. Includes the breakdown of rock by acidic water to produce clay Carbonic acid reacts with a new kind of mineral called a silicate and forms new soft clay mineral. The silicate s potassium, sodium, and magnesium ions are dissolved and carried away in solution. The clay left behind decays into soil or mineral deposits.

23 Oxidation Involves the reaction of metallic minerals in rocks to the oxygen in water. The result of the reaction is a new mineral called an oxide.