Lecture 20 - Mass Wasting Part 2

Question 1

fall

Answer 1

a material dropping through air, vertically or almost vertically

Question 2

slide

Answer 2

a material movie as a mass along a sloping surface (there is no internal motion within the mass itself)

Question 3

flow

Answer 3

downslope movement of a material that also has internal motion, like a fluid (eg. water, lava)

Question 4

regardless of name, most mass wasting examples include two or more of the following: ____

Answer 4

fall, slide, or flow

Question 5

falls are an extremely __ or very ___ form of mass wasting seen with ___ and ____

Answer 5

rapid
rapid

rocks (rockfall)
unconsolidated materials (soil fall)

Question 6

rockfalls

Answer 6

• rapid downslope movement of dislodges rocks that originates above a steep enough slope
• rocks may experience falling, rolling, bouncing, and/or sliding
• falling rocks include broken chunks from bedrock outcrops or boulders coming down mountain slides/cliffs

Question 7

bedrock

Answer 7

• hard, solid sock (ie. consolidated rock) under unconsolidated surface materials such as soil, sand or gravel
• can extend hundreds of meters below earths surface
• exposed (ie. above earths surface) bedrock seen on mountain tops, along coastlines, in quarries and on plateaus

Question 8

plateau

Answer 8

region of relatively level/flat ground with a higher elevation than surrounding area

Question 9

outcrops

Answer 9

visible exposures of bedrock occurring due to erosion or tectonic plate activity

Question 10

hydrostatic pressure

Answer 10

pressure exerted by any fluid (eg. water) in a confined space

Question 11

rockfalls and soil falls can also be driven by:
(other than factors discussed in previous lecture — shear force, shear strength, rock strength)

Answer 11

• hydrostatic pressure and the presence of water in bedrock cracks
• freeze (ie. expansion) and thaw (ie. contraction) cycles
• heavy snowfall and subsequent melt
• plant roots in bedrock cracks
• erosion by rivers/streams and/or wave action below (aka. undercutting)
• quarrying (ie. mining) activities

Question 12

slides can range from extremely ___ to extremely __. this form of mass wasting is seen with __ and __

Answer 12

slow
rapid

rocks
unconsolidated materials such

Question 13

types of slides

Answer 13

• rock slide
• rock avalanche
• slump

Question 14

rock slide

Answer 14

• sliding motion of rocks along a sloped surface
• can range from very slow to moderately fast

Question 15

rock avalanche

Answer 15

• sliding motion of rocks along a sloped surface
• larger rocks moving downhill quickly (at speeds on the order of meters/second) fragment (ie. breaks down) to form smaller rocks/pieces that keep moving downhill /slope

Question 16

slump

Answer 16

• sliding encountered when have thick (>10 meters) layer/slice of unconsolidated material on a curved slope
• (may also observe same for rock layer on curved slope)
• can occur extremely slowly to moderately fast
• mass of unconsolidated material gradually moves downward and spread outward
• often caused by presence of excess water between unconsolidated layer and served slope

Question 17

types of flows

Answer 17

• creep
• mudflows
• debris flows

Question 18

what’s a creep

Answer 18

• very slow (mm/year to cm/year) movement of soil/unconsolidated materials down a slope
• prevalent on sloped surfaces
• an example of very slow flow but difficult to rule out some sliding in many cases
• results in cracked roads
• results in trees, fenceposts, grave markers, etc… that lean downhill

Question 19

trees exposed to creep end up with ___

Answer 19

curved lower trunk

Question 20

curved trunk is also known as ___

Answer 20

pistol butt

Question 21

flows can range from extremely ___ to extremely ___. this form of mass wasting is generally associated with unconsolidated materials

Answer 21

slow
rapid

Question 22

creep down a sloped surface can be enhanced by (3)

Answer 22

• frozen subsoil preventing water drainage and wet materials down above slowly moves downhill
  -freeze/thaw
• frequent wetting/drying of soil

Question 23

what is solifluction

Answer 23

• creep triggered by freeze-thaw in colder climates
• gradual movement of wet soil/wet unconsolidated materials down a slope

Question 24

what are mudflows and debris flows

Answer 24

• often rapid and extremely raid movement of soil/sediment/unconsolidated materials down a slope

sediment/unconsolidated materials saturated with water (eg. due to heavy rain, ice/snow thaw) lose strength and ability to stay/stick together

sediment/unconsolidated material grains are pushed apart to extent that saturated mixture can actually flow

Question 25

in mudflows and debris flows, since sediment/unconsolidated materials are saturated with water, the flow can occur even down ____

Answer 25

gentle slopes

Question 26

mudflow

Answer 26

flow of (water) saturated unconsolidated materials down whose grains are sand-sized or smaller

Question 27

debris flow

Answer 27

flow of (water) saturated unconsolidated material whose grinds are gravel-sized or larger

Question 28

scientists classify soil into …. show the order biggest to smallest

Answer 28

gravel/stones, sand, silt, clay

Question 29

what is pore space

Answer 29

the space that exists between soil particles

Question 30

what is pore size

Answer 30

size of spaces that exist between soil particles

Question 31

when all pore spaces (ie, the entire pore volume) is filled with water, the soil is __

Answer 31

saturated

Question 32

as debris flows involve movement of ___ particles than mudflows, they typically require ___ than mudflows

Answer 32

larger steeper slopes

Question 33

example of a common process resulting in debris flow

Answer 33

1. unconsolidated material from a stream or riverbank collapse into the water 2. unconsolidated materials initially blocks water flow, then becomes saturated, ultimately mixing and flowing with water 3. major and sudden downstream flow of previously blocked water + saturated unconsolidated materials occurs, potentially causing significant damage (downstream)

Question 34

what can cause mudflows and debris flows

Answer 34

volcanoes

Question 35

___ can suddenly melt ice/snow

Answer 35

volcanic activity

Question 36

melted ice/snow can saturate unconsolidated materials, causing ____

Answer 36

causing said materials to flow downstream/down slope with water

Question 37

lahar

Answer 37

mudflows and debris flows occurring on a volcano or associated with volcanic activity

Question 38

__ is a flowing mixture of water, debris, volcanic and unconsolidated material

Answer 38

lahar

Question 39

topple

Answer 39

- forward rotation and movement of a mass/slice of rock or unconsolidated material (earth, debris) our of a slope - can occur extremely slowly or rapidly - triggered by factors including ice/snow thaw, weathering, undercutting and fluvial erosion - results in formation of debris pile (ie. debris cone or talus cone) at base of slope

Question 40

talus cone

Answer 40

a debris or rock pile at base of slope/mountain/hill

Question 41

what is the head scarp and toe of a slump

Answer 41

head scarp is the top toe is the bottom (see image no slide 10)

Question 42

debris

Answer 42

loose, natural material consisting especially of broken pieces of rock

Question 43

erosion

Answer 43

geological process in which material are worn away and potentially transported naturally by wind or water

Question 44

undercutting

Answer 44

erosion of material at the foot of cliff or steep slope

Question 45

fluvial erosion

Answer 45

erosion caused by flowing water (on the adjacent rock/unconsolidated materials

Question 46

weathering

Answer 46

breaking down or dissolving rocks and mineral on Earth’s surface

Question 47

factors that drive weathering

Answer 47

- water - ice/snow - acids - salts - plants - animals - temperature fluctuations

Question 48

once rocks broken down into its of rocks and minerals, ___ can transport these bits away

Answer 48

erosion

Question 49

how are erosion and weathering different

Answer 49

both involve breakdown of materials erosion: generally implies worn-down materials are transported away weathering: materials are also worn down but not transported away

Question 50

landslide

Answer 50

- failure and downslope movement of rock or unconsolidated materials due to gravity - movement of rock or unconsolidated material (debris or earth) mass down a slope due to gravity landslide = mass wasting (aka slope failure)