Chapter 5:  Erosion and Deposition

BIG IDEA:  Water, wind, and ice shape Earth’s Surface.

KEY CONCEPTS:

5.1  Forces wear down and build up Earth’s surface.

5.2  Moving water shapes land.

5.3  Waves and wind shape land.

5.4  Glaciers carve land and move sediments.

 

I.  5.1 FORCES WEAR DOWN AND BUILD UP THE EARTH’S SURFACE.

A. VOCABULARY:

1. erosion- the process in which weathered particles are picked up and moved from one place to another. 

2. deposition- the part of the erosion process in which sediment is placed in a new location.

3. mass wasting- the downhill movement of masses of rock and soil.

II.  NATURAL FORCES MOVE AND DEPOSIT SEDIMENTS.

A.  Erosion has a constant impact on the Earth’s surface. 

B.  Over millions of years, it wears down mountains by removing by-products of weathering and depositing them elsewhere.

C.  The force of gravity plays a major role in erosion and deposition.

1.  Gravity causes water to move downward, carrying and depositing sediment as it flows.  Gravity can pull ice slowly down mountain valleys.  And it causes dust carried by the wind to fall to the ground. 

D.  Erosion occurs in three major ways:

1.  Water- Rainwater and water from melting snow flow down sloping land, carrying rock and soil particles.  This water makes its way to a river, where it deposits more sediment, especially on the river bottom, banks, flood plain, or near its mouth.  Ocean waves also deposit sediment on beaches and coastlines.

2.  Wind- Strong winds can carry dust particles long distances.  Wind can also push large particles along the ground. 

3.  Ice- As ice moves slowly downhill, it transports rock and soil particles that are embedded in it. 

III. GRAVITY CAN MOVE LARGE AMOUNTS OF ROCK AND SOIL.

    A.  A landslide is one type of mass wasting.

    B.  In mass wasting, gravity pulls material downward, either gradually or suddenly.

    C.  Triggering events (earthquakes, heavy rain) loosen rock and soil.

    D.  Mass wasting includes rockfalls and rockslides.

         1. Rockfalls- Individual blocks of rock drop suddenly and fall freely.

         2. Rockslides- A large mass of rock slides as a unit down a slope.

     E. Mudflow

         1. Mass wasting of debris- a mixture of rock, soil and plants.

         2. Mudflows consist of debris mixed with a large amount of water.

         3. Often happens in mountain canyons and valleys after heavy rains.

         4. Can happen very quickly and cause many deaths.

         5. Volcanic mudflows

a. Pyroclastic flow- Cloud of fluidized rock and gases that moves   quickly as a result of gravity

b. Lahar- Similar to a pyroclastic flow but containing more water

F. Slumps and Creep

         1. Mass wasting on hilly land.

         2. Much less dramatic than rockslides or mudflows, but more common.

         3. Slump- A slide of loose debris that moves as a single unit. 

a. Usually occur along roads and highways where construction has made slopes unstable.

b. Can be triggered by heavy rain.

         4. Creep- The slowest form of mass movement of soil or debris.

                  a. Soil moves at about a rate of 1-10mm/year.

b. Evidence of creep can be seen along hillsides with old fences or telephone poles.  Fences or poles lean downward, or are out of line.