Erosion and Weathering

Forces of mechanical weathering are...

animal actions, freezing and thawing, plant growth, release of pressure, abrasion

animal actions

Animals that burrow in the ground- including moles, gophers, prairie dogs, and some insects- loosen and break apart rocks in the soil.

release of pressure

As erosion removes material from the surface of a mass of rock, pressure on the rock is reduced. This release of pressure causes the outside of the rock to crack and flake off like the layers of an onion.

Climate

Both chemical and mechanical weathering occur faster in wet climates. Chemical reactions occur faster at high temperatures: chemical weathering occurs more quickly where the climate is both hot and wet.

How might more than one agent of mechanical weathering operate in the same place?

Freezing and thawing could cause cracks that plant roots then make larger.

Give an example of rocks you have seen that were changed by natural processes.

I saw a round rock on the beach that had been smoothed by water.

What's the difference between mechanical and chemical weathering?

In mechanical weathering, rock is physically broken into smaller pieces. In chemical weathering, rock is broken down through chemical changes.

oxygen

Iron combines with oxygen in the presence of water in a process called oxidation. The product of iron oxidation is rust. Rust makes rock soft and crumbly and gives it a red or brown color.

plant growth

Plant roots enter cracks in rocks. As roots grow, they force the cracks apart. Over time, the roots of even small plants can pry apart cracked rocks.

abrasion

Sand and other rock particles that are carried by wind, water, or ice can war away exposed rock surfaces like sandpaper on wood.

The Sierra Nevada are much younger than the Appalachians. How might the Sierras change in the future? Explain.

The Sierras will probably become lower and more rounded. Older mountains have eroded more.

acid rain

The burning of coal, oil, and gas for energy pollutes the air with sulfur, carbon, and nitrogen compounds. The compounds react with water vapor in clouds, making acids that are stronger than normal rainwater. These acids mix with raindrops and fall as acid rain, which causes very rapid chemical weathering of rock.

Type of Rock

The minerals that make up the rock determine how fast it weathers. Permeable rocks weather more easily because they are full of tiny, connected air spaces that allow water to seep through it, increasing the surface area of the rock.

What factors determine the rate of weathering?

The most important factors that determine the rate at which weathering occurs are the type of rock and the climate.

Why are tombstones in a cemetery useful for comparing rates of weathering?

The stones are dated, so you know how long they have been exposed to weathering in the same area.

If a rock was broken into pieces, how much would the surface area increase? How would the rate of weathering change?

The surface area doubles. The rate of weathering would increase.

Why does permeable rock weather more quickly than less permeable rock?

Water reaches more of the rock's area, carrying chemicals that dissolve minerals.

What's the difference between weathering and erosion?

Weathering is the process that breaks down rock and other substances. Erosion is the process of wearing down and carrying away rocks.

carbon dioxide

When carbon dioxide in the air dissolves in water, a weak acid called carbonic acid forms. Carbonic acid weathers some kinds of rocks, such as marble and limestone.

living organisms

When plant's roots grow, they produce weak acids that slowly dissolve rock around the roots. Lichens- plantlike organisms that grow on rocks- also produce weak acids.

freezing and thawing

When water freezes in a crack in a rock, it expands and makes the crack bigger. the process of frost wedging also widens cracks in sidewalks and causes potholes in streets.

What are two processes that break down rocks on Mars?

blowing sand and acid-filled fog

Now I know that erosion and weathering...

break down and carry away rocks at Earth's surface

Which agent of chemical weathering most likely would form a limestone cavern?

carbon dioxide dissolved in water

Now I know that weathering is caused by

mechanical and chemical processes

Many ancient monuments are made of marble. Some are located in highly polluted cities. How might the pollution affect the monuments?

the pollution might lead to more acid rain, which would cause faster weathering

Now I know that the rate of weathering depends on...

the type of rock and climate

water

water weathers some rock by dissolving it

Agents of chemical weathering

water, oxygen, carbon dioxide, living organisms, acid rain

Mechanical

weathering physically breaks rock into smaller pieces