Topic 6 Geohazard II - Mass Movement

Question 1

Weathering

Answer 1

The process by which solid rock is dissolved and broken apart into smaller fragments

Question 2

Erosion

Answer 2

the scouring and stripping away of rock fragments loosened by weathering

Question 3

sediment transport

Answer 3

the movement of rock fragments (sediment) that have been weathered and eroded

Question 4

deposition

Answer 4

the laying down of sediment carried by Earth surface processes

Question 5

Bedrock slopes

Answer 5

talus slope created by rockfall from cliffs above.

usually found in arid regions (little to no rain) or arctic/high-alpine regions

Question 6

Soil-mantled slopes

Answer 6

convex slope dominated by diffusive processes

found where climatic conditions allow soil development and maintenance (humid and temperate climate)

Question 7

Mass movement (mass wasting)

Answer 7

Downslope movement of soil or rock material under the influence of gravity without the direct aid of water, wind or ice

occurs when Driving Forces > Resisting Forces

Driving forces = Gravity
Resisting Forces = Friction & Cohesion (strength of material)

Question 8

Angle of Repose

Answer 8

Maximum angle that loose material forming a slope can maintain and settle without slipping
Common angles:
Sand: 30-33 degrees
solid rock: up to 90 degrees
Snow avalanche: 30-50 degrees

Question 9

What are Mass Movement Triggering mechanisms?

Answer 9

Earthquakes
increased water content (rainstorms)
Decrease in slope strength due to (physical, chemical, anthropogenic, or biological) weathering

Question 10

Soil Creep

Answer 10

Slow downslope movement of soil & rock, due to expansion & contraction of surface materials

common rates of movement:
0.1-15mm/year
Limited to upper part of soil

Question 11

Solifluction

Answer 11

Rapid soil creep
Freeze-thaw, expansion-contraction

simplified: top layer is saturated while lower layer is frozen ground still, resulting in top layer sliding

Question 12

Types of slides

Answer 12

Slide: downslope movement of blocks of soil/rock along a thin and well-defined shear plane

Translational slides (landslides): have a straight failure surface

Rotational slides (slumps): have a curved concave failure

Question 13

Flow

Answer 13

a general term that includes any mass movement that have large amounts of water mixed into it

Mud flow: fast-moving flow composed mostly of mud
Debris flow: fast-flowing slurry of mud mixed with large objects, such as rocks and vegetation
Earth flow: flow composed mainly by clay-rich soil in which large elements are absent

Question 14

Fall

Answer 14

detachment of soil or rocks and downward motion by falling, bouncing or rolling with almost no interaction with other materials

Rockfall: occurs when rocks tumble off a vertical or nearly vertical cliff face

Question 15

Talus (scree)

Answer 15

pieces of angular broken rock that accumulate at the base of a steep slope or vertical cliff