Mass Wasting

Question 1

What is the meaning of “mass wasting”?
Give some examples.

Answer 1

The downhill movement of material on slopes.

Happy isles, Yosemite.

Question 2

What natural events can set off (or
trigger) mass movements on slopes?

Answer 2

Gravity - limited rock and soil strength

Slope angle - above and earthquakes

Orientation of bedding plane- geologic structure

water - storms

combinations of above - combination of above

Question 3

How is the risk of a mass movement
related to slope angle?

Answer 3

Material on a vertical cliff is pulled with the full force of gravity. Lesser slopes with less. So higher angle slopes are more unstable.

Question 4

How is the risk of a mass movement
related to the orientation of the
sedimentary bedrock?

Answer 4

the parallel strata are at greater risk of landsliding, or movement

Question 5

How is the risk of a mass movement
related to the presence (or absence) of
rainfall on slopes?

Answer 5

A volume of soil becomes heavier due to the water displacing air in the soil. And the water acts as a lubricant between the loose grains.

Both factors act in the direction of increasing the risk of mass movement. The heavier weight for a volume of soil increases the force of shear, and the lubricating effect of the water decreases the force of friction. Both of these changes in forces promote a mass movement, and make the slope more dangerous than when it was dry.

Question 6

What are the names of the two forces that
act on masses resting on slopes? How do
each of these forces act on the mass and
contribute to the stability (or instability) of
slopes?

Answer 6

Friction -keeps the mass from sliding downward

Shear - pulls the mass downwards.

Question 7

On slopes, how does mass “flow” differ
from “slip”?

Answer 7

flow or creep is fluid that changes shape

slip or slump is solid sliding on surface

Question 8

Describe some characteristics of the
movement a debris flow on a slope.

Answer 8

shape is different from location of origin

Question 9

Describe some characteristics of the
movement of a mudflow on a slope.

Question 10

Describe some characteristics of the
movement of soil creep on a slope?

Answer 10

the loose particles of soil act independently, and they move by small increments downslope over many years.

Question 11

Mass movements that occur on Earth
cannot occur on the Moon or Mars
because these planetary bodies have no
water – right? Explain.

Answer 11

Wrong, these things can happen and have.

Question 12

What factor(s) in nature “conspired to
 cause” the Madison Canyon slide?

Question 13

Can we say that some slope failures are
“man-made” disasters? Explain, using the
Festival Center mall failure as an
example.

Question 14

Describe some methods by which an
engineer (or nature) stabilizes a slope
against failure.

Answer 14

rock ties or vegetatiomn

Question 15

What type of mass movement did the La
Conchita, California failure exhibit? What trigger likely played an important role in this catastrophe?

Question 16

What evidence would you look for to
determine if the hillside about the motel in
which you were staying was potentially
hazardous?

Question 17

This is an example of … ?

Answer 17

Slip