Geology Reference
In-Depth Information
Chapter 11
Gravity Takes Its Toll: Mass
Wasting
In This Chapter
Understanding how gravity and friction work against each other
Figuring out what makes a slope stable
Adding water and other factors that trigger mass wasting
Moving soil and rock quickly: Falls, slides, slumps, and flows
Creeping down hillsides and other slow mass wasting
M
ass wasting
is the movement of large amounts of earth materials, such as rocks, sedi-
ments, and soil, down a slope in response to gravity. (As I explain in Chapter 7,
sediments
are loose particles of weathered rock.) Also called
mass movement,
mass wasting occurs
anywhere the land surface isn't completely flat. You are most likely familiar with this
movement in the form of landslides and rock falls.
What causes mass wasting? It's the response of earth materials to the constant pull of
gravity.
Gravity
is the force that keeps things “grounded” on earth — the same force that
ensures your bread will land butter-side down when it falls off the table or promises that
what goes up, must come down.
If you've ever stood at the top of a steep hill, you've experienced the pull of gravity down
a slope. If you're facing downhill, to stay at the top you must use all your leg muscles and
probably lean backward a little. The force of gravity encourages you to tumble forward,
and it takes a good bit of energy for you to fight that pull. The steeper the slope you are
standing on, the harder you have to work to resist the pull.
Gravity exerts the same pull on rocks, sediments, and soil. In this chapter, I explain what
prevents earth materials from sliding down a slope. I also discuss factors that trigger
mass wasting and define the various types of mass wasting.
