Points to Consider
- What features would you look for around where you live, to determine if glaciers had
ever been present there? - If glaciers had never formed on Earth, how would that affect the type of soil in the
middle of North America? - Can the process of erosion produce landforms that are beautiful?
10.5 Erosion and Deposition by Gravity
Lesson Objectives
- Describe the ways that material can move downhill by gravity.
- Discuss the factors that increase the possibility of landslides.
- Describe the different types of gravity driven movement of rock and soil.
- Describe ways to prevent and be aware of potential landslides or mudflows.
Introduction
So far in this chapter, you have learned about erosion and deposition by moving water in
rivers and the ocean, erosion and deposition by glacial ice and erosion and deposition by
wind. With this long list, you may think that we have covered all the types of erosion and
deposition that can possibly occur. The force you may have forgotten is gravity! Perhaps
because it is a constant force or perhaps because it is invisible, students often forget that
gravity also acts to shape the Earth’s surface. The examples we will consider here include
sudden, dramatic events likelandslides,as well as slow steady movements that happen over
long periods of time. Whatever the example, we know that the force of gravity will always
be there and it is changing the Earth’s surface right now.
Gravity Moves Material Downhill
There are several ways that gravity can move material from a higher place to a lower one.
Sometimes this happens along a cliff or a very steep slope. Material that has been loosened
by some type of weathering simply falls away from the cliff because there is nothing to keep
it in place. If you were to keep nudging your notebook towards the edge of your desk,
eventually enough of the notebook would be off the desk to cause it to fall. Landslides
happen when large amounts of rock suddenly fall down a cliff or mountainside.
Other times gravity simply makes things slide along rather slowly. You may have seen this
as a classmate moves further and further down in their seat. It’s not a very fast or dramatic