Chapter 13: Landslides and Other Mass Movements

Question 1

regolith

Answer 1

soil and loose sediment or debris

Question 2

mass movement

Answer 2

aka mass wasting

the downslope transport of rock, snow, and ice

Question 3

landslide

Answer 3

mass movement of rock or regolith down a slope

Question 4

four features that help classify types of mass movement

Answer 4

1. material involved
2. velocity of the movement (slow, intermediate, or fast)
3. character of the moving mass (coherent or chaotic; wet or dry)
4. the environment in which the movement takes place

Question 5

creep

Answer 5

refers to the slow, gradual downslope movement of regolith on a slope; happens when regolith alternatively expands and contracts in response to freezing and thawing, wetting and drying, or warming and cooling.

Question 6

solifluction

Answer 6

in areas where permafrost exist, the summer months might allow the top few inches to thaw, but the water cannot seep down so the ground becomes soggy and eventually flows or moves in the direction of the slope

Question 7

slump

Answer 7

moving rock or regolith does not disintegrate but rather stays somewhat coherent

Question 8

failure surface

Answer 8

the point or plane where a slump block slides over/on; some are planar, but commonly they curve and resemble a spoon lying concave side up

Question 9

mudflow

Answer 9

a moving slurry of mud, aka mudslide

Question 10

debris flow

Answer 10

a slurry consisting of a mixture of mud and larger, pebble to boulder sized fragments

Question 11

lahars

Answer 11

devastating mudflows that spill down valleys bordering volcanoes and consist of a mixture of volcanic ash and water from the snow and ice that melts in volcanoes heat or from heavy rains

Question 12

rockslide

Answer 12

a sudden movement of rock and debris down a non-vertical slope (debris slide if it consists of mostly regolith)

Question 13

snow avalanche

Answer 13

a chaotic jumble of snow surging downslope; can occur when a cornice (a large drift of snow that builds up on the lee side of a windy mountain summit) suddenly gives way and falls onto slopes below and knocks free additional snow

Question 14

what triggers rock/debris falls?

Answer 14

when a body of rock separates from a cliff face along a joint (a natural crack in rock)

Question 15

talus

Answer 15

a sloping apron of rocks along the base of the cliff

Question 16

marine slumps

Answer 16

semi-coherent blocks slip downslope on weak horizons

Question 17

turbidity currents

Answer 17

sediment disperses in water to yield a turbulent cloud of suspended sediment that rushes downslope as a submarine avalanche or density current.

Question 18

what elements contribute to mass movement

Answer 18

1. fracturing and weathering of the substrate; weakens substrate so it cannot hold up against the pull of gravity
2. the development of relief which provides slopes down which masses move;
3. an event that sets mass in motion

Question 19

slope failure

Answer 19

when material starts moving on an unstable slope

Question 20

what does slope failure depend on?

Answer 20

the balance between two forces:

• downslope force (inhibits sliding)
• resistance force (inhibits sliding)

Question 21

angle of repose

Answer 21

when granular debris piles up to form the steepest slope it can without collapsing; also dependent on water content

• fine sand 30deg
• coarse sand 45deg
• angular pebbles 45deg

Question 22

what causes slope failure?

Answer 22

• shocks, vibrations, and liquification
• changing slop loads, steepness, and support
• changing slope strength; can be due to weathering, vegetation cover, and water content

Question 23

head scarp

Answer 23

a hill side where a slump block has move away(down), forms a scar; at the opposite end of the slump is the “bulging toe”

Question 24

movement occurs wen ___ > _____

Answer 24

downslope force > resisting force

Question 25

colluvium

Answer 25

poorly sorted, poorly stratified or unstratified sediment; forms due to mass wasting or other downslope movement.