Lecture 20 - Mass Wasting Part 2 Flashcards
fall
a material dropping through air, vertically or almost vertically
slide
a material movie as a mass along a sloping surface (there is no internal motion within the mass itself)
flow
downslope movement of a material that also has internal motion, like a fluid (eg. water, lava)
regardless of name, most mass wasting examples include two or more of the following: ____
fall, slide, or flow
falls are an extremely __ or very ___ form of mass wasting seen with ___ and ____
rapid
rapid
rocks (rockfall)
unconsolidated materials (soil fall)
rockfalls
- 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
bedrock
- 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
plateau
region of relatively level/flat ground with a higher elevation than surrounding area
outcrops
visible exposures of bedrock occurring due to erosion or tectonic plate activity
hydrostatic pressure
pressure exerted by any fluid (eg. water) in a confined space
rockfalls and soil falls can also be driven by:
(other than factors discussed in previous lecture — shear force, shear strength, rock strength)
- 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
slides can range from extremely ___ to extremely __. this form of mass wasting is seen with __ and __
slow
rapid
rocks
unconsolidated materials such
types of slides
- rock slide
- rock avalanche
- slump
rock slide
- sliding motion of rocks along a sloped surface
- can range from very slow to moderately fast
rock avalanche
- 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
slump
- 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
types of flows
- creep
- mudflows
- debris flows
what’s a creep
- 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
trees exposed to creep end up with ___
curved lower trunk
curved trunk is also known as ___
pistol butt
flows can range from extremely ___ to extremely ___. this form of mass wasting is generally associated with unconsolidated materials
slow
rapid
creep down a sloped surface can be enhanced by (3)
- frozen subsoil preventing water drainage and wet materials down above slowly moves downhill
-freeze/thaw - frequent wetting/drying of soil
what is solifluction
- creep triggered by freeze-thaw in colder climates
- gradual movement of wet soil/wet unconsolidated materials down a slope
what are mudflows and debris flows
- 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
in mudflows and debris flows, since sediment/unconsolidated materials are saturated with water, the flow can occur even down ____
gentle slopes
mudflow
flow of (water) saturated unconsolidated materials down whose grains are sand-sized or smaller
debris flow
flow of (water) saturated unconsolidated material whose grinds are gravel-sized or larger
scientists classify soil into ….
show the order biggest to smallest
gravel/stones, sand, silt, clay
what is pore space
the space that exists between soil particles
what is pore size
size of spaces that exist between soil particles
when all pore spaces (ie, the entire pore volume) is filled with water, the soil is __
saturated
as debris flows involve movement of ___ particles than mudflows, they typically require ___ than mudflows
larger
steeper slopes
example of a common process resulting in debris flow
- unconsolidated material from a stream or riverbank collapse into the water
- unconsolidated materials initially blocks water flow, then becomes saturated, ultimately mixing and flowing with water
- major and sudden downstream flow of previously blocked water + saturated unconsolidated materials occurs, potentially causing significant damage (downstream)
what can cause mudflows and debris flows
volcanoes
___ can suddenly melt ice/snow
volcanic activity
melted ice/snow can saturate unconsolidated materials, causing ____
causing said materials to flow downstream/down slope with water
lahar
mudflows and debris flows occurring on a volcano or associated with volcanic activity
__ is a flowing mixture of water, debris, volcanic and unconsolidated material
lahar
topple
- 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
talus cone
a debris or rock pile at base of slope/mountain/hill
what is the head scarp and toe of a slump
head scarp is the top
toe is the bottom (see image no slide 10)
debris
loose, natural material consisting especially of broken pieces of rock
erosion
geological process in which material are worn away and potentially transported naturally by wind or water
undercutting
erosion of material at the foot of cliff or steep slope
fluvial erosion
erosion caused by flowing water (on the adjacent rock/unconsolidated materials
weathering
breaking down or dissolving rocks and mineral on Earth’s surface
factors that drive weathering
- water
- ice/snow
- acids
- salts
- plants
- animals
- temperature fluctuations
once rocks broken down into its of rocks and minerals, ___ can transport these bits away
erosion
how are erosion and weathering different
both involve breakdown of materials
erosion: generally implies worn-down materials are transported away
weathering: materials are also worn down but not transported away
landslide
- 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)
