Ch4L3: Changing Earth's Surface

Chapter 4 Lesson 3

Changing Earth's Surface

Breaking Down Earth's Materials

• Weathering: refers to the mechanical and chemical processes that change Earth's surface over time. It can break, scrape, smoot, or chemically change rock.

• Sediment: is the material formed from rocks broken down by weathering. Sediment can be rock fragments, sand, silt, or clay.

Physical Weathering

• Physical Weathering: the process of breaking down rock without changing the composition of the rock.

• Natural Processes - for example a boulder that rolls off a cliff and breaks apart.

• Weather Changes - If it's cold enough for water to freeze, it will expand, this can shatter rocks.

• Plants and animals can also break rocks.

Chemical Weathering

• Chemical Weathering: is the process that changes the composition of rocks.

• Some minerals react with water, or substances in water and air, such as carbon dioxide.

• Limestone contains calcite that dissolves in slightly acidic water.

• Chemical weathering happens faster in places with water and warm temperatures. It can weaken rocks, breaking them easier.

Concept Check

What is the difference between physical and chemical weathering?

What is the difference between physical and chemical weathering?

Physical weathering breaks rocks without changing the rock's composition.

Chemical weathering changes the rock's composition.

Moving Earth Materials

• Mountains wear away for many reasons. We have already discussed weathering, which leads to slow changes.

• Gravity can cause mass wasting, the downhill movement of a large mass of rocks or soil due to gravity.

• Also known as landslides, they can also be caused by flowing water, wind, and moving ice.

Moving Earth Materials

• Water flows fastest where land is steep. Large rivers cause the most erosion as the water flows faster.

• Slowly flowing water has less energy and can carry less sediment.

• Sediment can be deposited on the sides of rivers, or when rivers enter oceans or lakes, creating land features called deltas.

Moving Earth Materials

• Sometimes, wind is strong enough to cause erosion.

• In deserts, erosion caused by wind can be the most important process that changes landforms.

• Wind can slowly weather and erode solid rock, and also pick up sand grains and carry them from one place to another, creating sand dunes.

Concept Check

What provides the forces that can cause rock to move downhill?

What provides the forces that can cause rock to move downhill?

Gravity.

Ice

• Glaciers: large masses of ice, formed by snow accumulation on land, that move slowly across Earth's surface.

• The force of gravity causes ice to flow downhill.

• Sliding and flowing ice can weather the rocks they move over.

• Glaciers can carve deep valleys. They deposit sediment when they melt.

Multiple Choice

On steep slopes, gravity causes:

• chemical weathering

• mass wasting

• physical weathering

• strong winds

Predict

How would increased temperatures and precipitation affect a mountain?

How would increased temperatures and precipitation affect a mountain?

Weathering happens faster in areas with abundant water and warm temperatures, so the mountain would have an increase in weathering which will lead to erosion and possible landslides.