Weathering and erosion

Question 1

What is weathering

Answer 1

It is a chemical surface or mechanical process that breaks rocks into smaller pieces.

Question 2

What is mechanical weathering?

Answer 2

Mechanical weathering breaks rocks into smaller pieces without changing them chemically. The small pieces are identical in composition to the original rock. Two causes of mechanical weathering are ice wedging and living organisms

Question 3

What are the causes of mechanical weathering?

Answer 3

1. Ice wedging
   When it rains or snow melts, water seeps into cracks in rocks. If the temperature drops enough the water will become ice. The crystals will grow and take up more space as when water freezes its molecules move apart. This expansion exerts pressure on rocks making them crack further.
2. Plants and animals
   Some plants grow in unusual places and their roots grow deep into cracks in rock where water collects. The roots slowly grow and further erode the rock. Animals that burrow go through the sediment breaking the rock apart.

Question 4

What is chemical weathering?

Answer 4

It occurs when the chemical composition of rock changes. This kind of weathering is rapid in tropical regions where it’s moist and warm. In other regions it is slow. Two important causes of chemical weathering are natural acids and oxygen.

Question 5

What are the causes of chemical weathering?

Answer 5

1. Natural acids
   Some rocks react chemically with natural acids in the environment. When water mixes with CO2 from the environment it forms carbonic acid that can dissolve rocks. Plants also produce a substance called tannic acids that dissolves with minerals in rocks tweaking them further.
2. Oxygen
   When iron-containing materials (cars, soil, rock, etc) are oxidized a chemical reaction causes the material to rust. When this happens to rocks it weakens the rock.

Question 6

What is soil?

Answer 6

Soil is a mixture of weathered rock, organic matter, water, and air that supports the growth of plant life. Organic matter includes decomposed plant debris and other materials.

Question 7

What are the factors that affect soil formation?

Answer 7

1. Slope of land
2. Time
3. Organisms
4. Parent Rock
5. Climate

Question 8

Factors that affect soil formation:
Parent rock

Answer 8

The kind of parent rock being weathered also affects the type of soil. Ex: Limestone is chemically weathered to become clayey soil, and Sandstone is weathered to become sandy soil.

Question 9

Factors that affect soil formation:
The slope of the land

Answer 9

The topography or surface features also affect soil formation. In steep areas soil has less chance of developing. This is because rock fragments move downhill constantly. In lowlands where the land is flat, wind and water deposit fine sediments that help form thick soils.

Question 10

Factors that affect soil formation:
Climate

Answer 10

In tropical places that are warm and humid rock weathers quickly, and deep soil can develop rapidly. Climate also affects the amount of organic material in the soil, tropical places are favorable again. When plants and animals die, decomposition by fungi and bacteria begins. The result is the formation of the humus. Humus helps soil hold water and provides nutrients to plants.

Question 11

Factors that affect soil formation:
Time

Answer 11

It takes time for rocks to weather. It can take thousands of years. In young soils, the parent rock determines the soil characteristics. As weathering continues the soil resembles the parent rock lesser and lesser. Thicker and well-developed soils are found in areas where weathering has gone on undisturbed. For this to happen soil materials must not be eroded and new sediment should be deposited too quickly.

Question 12

Factors that affect soil formation:
Organisms

Answer 12

Lichens are small organisms that consist of alga and fungi that live together for mutual benefit. As lichens grow they take nutrients from the rock that they are starting to break down forming a thin soil. The roots of plants further break down the parent rock. Areas that had any plants will have more organic matter and will have rich soil.

Question 13

What are the agents of erosion?

Answer 13

1. Gravity
2. Ice
3. Wind
4. Water.

Question 14

Agents of erosion:
Gravity

Answer 14

Gravity pulls everything towards the Earth’s center. When gravity alone causes rock or sediment to move down a slow erosion is called mass movement. There are types of mass movements
1. Creep: Sediments slowly move downhill. Common where freezing occurs. As the ice expands in the soil, it pushes sediments up. Then as soil thaws, the sediments move further down the slope.

2. Slump: A slump occurs when a mass of rock or sediments moves downhill. Slumps frequently occur on slopes that have been undercut by erosion, such as those above the bases of cliffs that have been eroded by waves.
3. Rock slides: Dring a rock slide layers of rock break lost from slopes and slide to the bottom. This produces a huge, jumbled pile of rocks at the bottom of the slope. Tock slides can be destructive.
4. Mudflows: A mudflow is a mass of wet sediment that flows downhill over the ground surface. Some mudflows can be thick and flow slowly downhill at rates of a few meters per day.

Question 15

Agents of erosion:
Ice

Answer 15

As glaciers move over Earth’s surface they erode materials from some areas and deposit sediment in other areas. There are two types of glaciers - continental and valley glaciers.
1. Glacial Erosion: If the underlying rock has cracks in it the ice can pull our pieces of rock. Scratching produces large grooves or smaller striations in the rock underneath. The scratching also can wear rock into a fine powder called rock flour.

2. Effects if Glacial erosion: In mountains, valley glaciers can remove rock from the mountaintops to form large bowls called cirques. When a glacier moves into a stream valley, it erodes rock along the valley sides producing a wider, U-shaped valley. Continental glaciers can scour large lakes and completely remove rock layers
3. Glacial Deposition: When ice melts at the bottom of a flowing glacier or along its edges, the sediment the ice was carrying gets left behind on the surface. This sediment is called till. Till is a large mixture of different-sized particles ranging from clay to large boulders. When glaciers melt their sediments are deposited in gravel and soil. Sand and gravel deposits laud down by streams are called outwash.

Question 16

Agents of erosion:
Wind

Answer 16

Wind often leaves behind particles too heavy to move. This erosion of the land by wind is called deflation. Deflation can lower the land’s surface by several meters. Wind with sediments can hit rocks and erode them like sandpaper. An abrasion is a form of erosion that can make pits in rocks and produce smooth, polished surfaces. When the wind blows around some irregular features like vegetation or rocks the wind slows down and the sediment is deposited. The wind carries only fine sediment called silt. Accumulation of silt is called loess and it can blanket Earth’s surface. Loess is often deposited downwind of large deserts and deflated glacial outwash deposits.

Question 17

Agents of erosion:
Water

Answer 17

Water that flows over the earth’s surface is called runoff.
1. Sheet flow: If raindrops are falling on a sloped land surface a thin sheet of water might begin to move downhill.

2. Rills and gullies: Where a sheet of water flows around obstacles and becomes deeper, drills can form. Rills are small channels cut into the sediment at the earth’s surface. When these channels become bigger they are called gullies.
3. Streams: Gullies often connect to stream channels. These streams have a lot of energy and often cut into the rock beneath their valleys. As streams move out of the mountains and onto flatter land they begin to flow more smoothly eroding and depositing sediments along their sides.