Mass wasting

Question 1

Mass wasting

Answer 1

Mass wasting is the downward movement of rock or soil on a hillside

Question 2

different forms of mass wasting

Answer 2

This movement occurs in a variety of forms, including falls, slumps, slides, creep, and flows

Question 3

Falls definition

Answer 3

Falls are sudden, abrupt landsliding
events characterized by relatively
large pieces of slope material that
move downslope in freefall, or by
tumbling, bounding, and rolling. If the
material rolls or rotates, it may be
called a topple.

Question 4

Creep definition

Answer 4

Creep (often called soil creep) is a slow but insidious
form of mass wasting. Although day to day changes may
be almost imperceptible, over a period of time the slope
movement and deformation can cause serious damage
to structures on the hillside.

Question 5

Slide definition

Answer 5

The term slide refers to mass
movements where there is a
zone of weakness, leading to
a distinct separation (fault)
between the slide material
and the stable underlying
hillside. The moving slide
material tends to retain its
structure and move as a unit

Question 6

Flow definition

Answer 6

A flow is the movement of hillside
materials as a fluid or slurry, usually
with a very high water content. Flows
are particularly dangerous because
they may move very rapidly
downhill. Flows of very fluid
materials on relatively flat slopes may
be called lateral spreads

Question 7

Driving force

Answer 7

The figure shows a generic diagram of how
the force of gravity (red arrow) can be
considered as two orthogonal forces
(represented as green arrows).
One acts directly down the slope and
impels the object to move downhill. This
force is called the driving force

Question 8

resisting force

Answer 8

The other force component is straight down
toward the ground surface, which in
conjunction with the friction between the
block and slope, acts to hold the object in
place. This force is called the resisting
force.

Question 9

equation forStability Factor (

Answer 9

SF = (resisting force)/(driving force)

Question 10

meaning for stabilty factor

Answer 10

The larger the SF, the more stable the hillside. If the value is greater than
1.0, the hillside is considered stable, and if the value is less than 1.0, the
hillside is considered unstable. Steeper slopes will have smaller SF values.

Question 11

Causes for landslides

Answer 11

-heavy rainfall
-slopes undercut
-earthquake

Question 12

Slopes undercut

Answer 12

Streambank erosion, as
well as construction, road-
building, and other human
activities, can change
(increase) the slope of a
hillside. Increasing the
effective slope increases the
landslide risk. The figure
shows how a road cut
creates a much steeper
hillside.

Question 13

Snow avalanches

Answer 13

A snow avalanches is a mass of falling snow and/or ice. It is a gravity-driven mass wasting process
analogous to landsliding.

Question 14

Loose snow avalanches

Answer 14

These resemble flow-type landslides; the material moves downhill as an
unconsolidated mass and may spread out as it goes. It generally occurs on packs composed of fresh
snow

Question 15

SLab avalanches

Answer 15

These move as cohesive blocks. The blocks are formed from snow that has settled,
compacted, ripened, and perhaps been through warming/freezing cycles

Question 16

There are two factors involved in avalanche risk assessment

Answer 16

angle of repose - This is the steepest angle at which a material can be piled before it starts to
collapse. The angle of repose of snow varies according to the physical properties and a
particular snowpack.
*slope of hillside - As with any mass wasting hazard, steeper slopes lead to greater risk.

Question 17

What slopes are at risk for an avalanch the most

Answer 17

The risk is greatest at slopes of 37-40% - hills with greater slopes have lesser risk; this is because at very
large slopes, the snow is so unstable that very little can accumulate, and any snow that falls will likely
move downslope by numerous, inconsequential mini-avalanches