Erosion reading
Erosion is the process by which natural forces move weathered rock and soil from one place to another. Gravity,
running water, glaciers, waves and wind all cause erosion. The material moved by erosion is sediment. When the
agents of erosion lay down sediment, deposition occurs. Deposition changed the shape of the land. Weathering,
erosion and deposition act together in a cycle that wear down and builds up the earth’s surface. Erosion and
deposition are at work everywhere on Earth. Sometimes, they work slowly. At other times, they work more quickly.
Erosion and deposition are never-ending.
Gravity pulls everything toward the center of Earth. Gravity is the force that pulls rock and soil down slopes.
Gravity causes mass movement, any one of several processes that move sediment downhill. Mass movement can be
rapid or slow. The different types of mass movement include landslides, mudslides, slump, and creep.
The most destructive type of mass movement is a landslide, which occurs when rock and soil slide quickly down a steep
slope. Some landslides may contain huge masses of rock, while others may contain only a small amount of rock and
soil.
A mudflow is the rapid movement of a mixture of water, rock, and soil. The amount of water in a mudflow can
be as high as 60 percent. Mudflows often occur after heavy rains in a normally dry area. In clay soils with high water
content, mudflows may occur even on very gentle slopes. An earthquake can trigger both mudflows and landslides.
In the type of mass movement known as slump, a mass of rock and soil suddenly slips down in one large mass. It
looks as if someone pulled the bottom out from under part of the slope. Slump often occurs when water soaks the
base of a mass of soil that is rich in clay.
Creep is the very slow downhill movement of rock and soil. It occurs most often on gentle slopes. Creep is so
slow that you can barely notice it, but you can see its effects in objects such as telephone poles, gravestones, and fence
posts. Creep may tilt these objects at unusual angles. Creep often results from the freezing and thawing of water in
cracked layers of rock beneath the soil.
1. What causes mass movements? ___________________________________________________________________
2. What are the four types of mass movement? _________________________________________________________
3. What is the difference between a mudflow and a landslide? _____________________________________________
______________________________________________________________________________________________
Identify each of the examples below by writing landslide, mudslide, slump, or creep.
________________________1. Watery clay soil slides down a mountain.
________________________2. A telephone poll leans downhill.
________________________3. Rock at the top of a cliff suddenly falls.
________________________4. As you step on the mountain path, bits of rock and soil fall downhill.
________________________5. After a heavy rainfall, soil on a desert hill slides to the bottom.
________________________6. After many years, a gravestone on a hillside falls over.
________________________7. Rock and soil suddenly slip downhill in one large mass.
________________________8. During an earthquake, rock and soil move down a slope.
Fill in the blank
1. The agents of erosion lay down sediment in new locations in a process called ________________________.
2. The material moved by erosion is called __________________________.
3. The process by which natural forces move weathered rock and soil from one place to another is called
___________________________.
4. _____________________________ included several processes caused by gravity that move sediment downhill.
SOIL
Use the terms to complete the sentences
water
Humus
A horizon
topsoil
evolve
profile
below
parent
composition
Bottom
top
infiltration
Soil
horizons
subsoil
1. ___________________ is a mixture of sediments of weathered rock and organic material.
2. Decaying plant and animal matter, found in soil is also called _________________________.
3. Due to weathering, different layers of soil, also called __________________________ form.
4. Soil generally has three layers, this makes up the soil ______________________.
5. The A horizon is the _______________ layer and is also known as ________________________.
6. The B horizon is the layer _______________ the A horizon.
7. The C horizon is the _______________ layer in a soil profile. Also known as _____________________.
8. Below the bottom horizon is the _________________ rock.
9. You can tell the ______________________ layer is the most fully evolved soil layer because it has more humus.
10. ____________ moving down through the layers of soil is called ___________________.
11. The thickness and _____________________ of soil layers depend on the climate, slope and type of rock.
12. Soil horizons _________________ more slowly in dry and cold climates.
Weathering
potholes
temperatures
acid rain
Rust
climate
Freezing
cracks
minerals
Chemical
Mechanical
moisture
Pressure
Frost wedging
Pieces
Weathering is the breaking of rocks into ____________________. There are two main types of weathering.
__________________ weathering involves breaking rocks without changing their chemical composition. In _________
____________, water trapped in rocks freezes and expands, forcing the rocks apart. _______________ can also cause
mechanical weathering. Plant roots put pressure in rocks and cause small _______________ to widen and split the rock.
______________________ weathering involves water, air and other substances’ to react with the minerals in rocks.
When metal is exposed to water and oxygen, oxidation occurs and __________ forms. Carbonic acid in plant roots and
mosses also react with the ______________ in rocks. Water and carbon dioxide form _______________ which
deteriorates many stones. How rapidly these changes occur depend on the ____________ of the area. Chemical
weathering happens more slowly in the desert because there is little _________________. Low ____________________
in polar regions keep weathering to a minimum there too. Whenever _______________ and thawing alternate,
mechanical weathering becomes very detrimental forming many ___________________ on the roadways.