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Mass Wasting (Mass Movement)

Mass wasting is the down slope movement of rock, soil, or other materials due to gravity. Mass wasting can occur very rapidly or very slowly, depending on the conditions of the slope. Mass wasting occurs both above and below water.

What Causes Mass Wasting?

Slopes are very common in nature. The sides of mountains and hills are all slopes. When a slope becomes unstable, the likelihood of mass wasting increases. This can happen for a variety of reasons. If the slope is exposed to weathering, the material it is made of will weaken. The weaker this material gets, the more likely that sediment will fall down the slope. Have you ever poured water into the dirt and watched it turn into mud? How does the mud differ from the dry soil? If you run your hands through it, it feels very soft. You could squish it through your fingers! This happens because the water has found its way between all the particles in the soil. The soil becomes almost likealiquid!
 
This same thing happens often in nature. A slope will weaken if it absorbs too much water, such as when a storm passes over a mountain. The more water the slope absorbs, the weaker it gets. Eventually, loose material will fall down the slope.
Slope collapse ending in landslide.

This slope collapsed after a heavy rain.

Vegetation plays a big role in stabilizing slopes. The strong root systems of trees and other plants help hold the soil in place. When these trees are removed, the soil becomes weak. This is why deforested areas are likely to be sites of mass wasting.

Types of Mass Wasting Events

A creep occurs when the material on a slope moves very slowly. Soil and rocks will inch their way down a slope due to the force of gravity.
 
A slide is when a mass of sediment sticks together and moves down a slope. Imagine sending a sled down a snowy hill. The composition of the sled doesn’t change as it moves down the slope. This is exactly what can happen to some sections of land.
 
A flow is when the soil and rock moving down a slope flows like a liquid. Mudflows and mudslides are examples of flows.
This mudflow is an example of mass wasting.

Mud, as part of a mudflow, has covered this part of the forest floor

 
A fall is when soil or rock fall off of a very steep slope and settles at the base of the structure. This material will pile up over time. Eventually, it may lead to the formation of a scree.

Other Great Resources

 
Mass Wasting – Mexus Education 

 
Written By: Francis Aguisanda.