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Physical Geology 101
26. Erosion and Mass Wasting
(p. 402-418)
Erosion
Where are two U.S. examples of where shoreline wave erosion is a major concern?
1. _____________________________
2. _____________________________
Where is shoreline erosion also a problem at a large lake? ___________________
Weathering involves the breakdown of rock to form loose particles called regolith. Any process that
involves the movement of this regolith from one location to another, and the abrasion of rocks hit by the
regolith as it gets transported, is termed erosion.
What 3 natural “elements” cause erosion?
1. _________________
2. _________________
3. _________________
What are the two characteristics of a flowing medium that play an important role in how effectively
material gets transported?
1. _________________ and 2. _________________
The resultant types of fluid motion are called ______________ and _______________.
Describe laminar flow: _____________________________
Is the flow speed high or low? ___________________________
Describe turbulent flow: ___________________________________
Is the flow speed high or low? ___________________________
Is turbulent flow more common in fluids with low or high viscosity? _________________
So which is more turbulent: water flow or wind gusts? ___________________
When pieces of regolith get lifted up off the ground and then bounce it along in small hops and jumps, we
call this process ___________________.
Mass Wasting
What fourth effect may cause a type of erosion called mass wasting? ___________________
What happens during mass wasting? _______________________________________________
The common term used to describe mass wasting is ___________________.
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Physical Geology 101
What main factors influence the motion of regolith down a slope?
1. ___________________________________________
2. ___________________________________________
3. ___________________________________________
4. ___________________________________________
5. ___________________________________________
The susceptibility of loose material to move down a slope is affected by the way the grains of the material
are packed together as well as the stickiness of the grains, which is called either the:
_____________________ or the _____________________
This stickiness of the grains determines a type of material strength called the:
_________________________
What is the definition of this type of strength? _________________________________________
The steepest angle that a slope can maintain without material tumbling down is called the:
_____________________________
What is the range for this angle in most types of regolith? _____________________
The steepness of piles of ____________ that collect at the bottom of a steep slope is controlled by the
angle of repose of the material.
Upsetting the angle of repose:
What activity by humans can induce landslide activity? ___________________________
Removal of vegetation may induce landslides because roots bind regolith particles together, keeping
them stable. Vegetation can be removed by humans or naturally by ______________.
How does the addition of water destabilize sediment on a hill? _________________________________
This is why landslides are common after ____________________.
What other natural phenomena can induce landslide activity?
_____________________ (causes collapse of river embankments)
_____________________ (e.g. Yungay, Peru, 1970: 25,000 deaths)
Types of Mass Wasting
The three criteria used for classifying the different types of landslides are:
1. _________________________________ (rapid or slow)
2. _________________________________ (falling, sliding, or flowing)
3. _________________________________ (rock, soil, or debris)
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Physical Geology 101
We can define two categories of mass wasting / landslides:

____________________: falling, sliding, or slumping of otherwise coherent bodies of rock due to
sudden failure on a steep slope or cliff.

____________________: fluid-like downslope movement of loose regolith.
What are the different types of mass wasting in each category?
SLIDES AND FALLS
SEDIMENT FLOWS
________________
_________________
________________
_________________
________________
_________________
_________________
_________________
Slides and Falls
What is a fall? ____________________________________________________
Example of where this is a problem: ____________________
What is a slide? ___________________________________________________
What is a slump? ___________________________________________________
Example of where slumping is common: ______________________
Sediment Flows
A sediment flow that is water-saturated is called a ____________________.
A sediment flow that is air-saturated is called a ____________________.
Water-saturated flows can occur very slowly in areas that typically receive lots of rainfall, and may form
bulging lobes of migrating regolith on slopes. This process is called _____________________.
What is the difference in the sediment size between a mudflow and a debris flow?
Mudflow: ________________________________________
Debris flow: ______________________________________
How fast can a mudflow flow? ________________
Examples of locations rapidly overwhelmed by mudflows:
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Physical Geology 101
(1) ___________________ in 1985 (lahar induced by a volcanic eruption)
(2) ___________________ in 2006 (caused by heavy rainfall)
When a thin layer of water-saturated surface material (e.g. soil) flows down a slope over a period of days,
months, or years, stabilized by a covering of grass, the flow is called an:
_________________________
A dangerous variety of granular flow in which blocks of regolith race down a slope at speeds of 100s of
mph, is called a ______________________.
e.g., Peru, 1970 (triggered by an earthquake) - 25,000 deaths in the city of Yungay.
A slow type of granular flow can cause the imperceptible down-slope motion of an entire hillside. Objects
on the surface eventually lean over. e.g. telephone poles, lampposts, fences, trees.
FINAL QUESTION:
What is this slow slope motion called? __________________
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