Geology 101 Quiz 10 Flashcards
mass wasting
large-scale movement of rock or sediment down slope
the terminology for mass wasting events is based on three criteria
nature of motion, material, speed
natures of motion as they apply to mass wasting events
fall (freefall)
slide (mass stays intact and moves down-slope as a unit)
flow (mass moves a fluid)
materials as they apply to mass wasting events
rock, unconsolidated material (non-lithified sediment)
speed as it applies to mass wasting events
slow (creep and solifluction)
moderate (slides, slumps, and flows)
fast (falls and avalanches)
creep
slow, uniform movement of soil
solifluction
creep of saturated soil over permafrost
permafrost
ground that remains frozen all year
how does solifluction occur
melting ice and snow during the summer saturates the soil on top of the permafrost; the saturated soil slowly flows down the slope forming rounded lobes
slump
slow or fast displacement of block
slide
movement of block parallel to surface (most common where thin rock layers are sloped and eroded)
flow
fast; debris becomes fluidized by water or air
fall/avalanche
free falling from cliff (fall) or bounding down steep slope (avalanche)
influences on slope stability
steepness of slope, composition, vegetation, water content,
steeper slopes are (less/more) stable
less
consolidated material is (less/more) stable
more
physical and chemical weathering weaken rock making is (less/more) stable
less
(smaller/larger) particles make LESS stable slopes
smaller
(rounded/angular) particles make LESS stable slopes
rounded
angle of repose
the maximum slope angle unconsolidated material can maintain
a stack of marbles will have a ? angle of repose
very low
a stack of angular fragments will have a ? angle of repose
high
fine sand has a (lower/higher) angle of repose than coarse sand
lower
vegetation generally (decreases/increases) slope stability and why?
increases; a network of roots through the soil
exceptions to vegetation increasing slope stability
root action that increases weathering, and heavy trees adding weight to an already weak overhang
increasing the water content generally (decreases/increases) slope stability, but not always
decreases
a small amount of water causes particles to adhere to each other due to surface tension, resulting in
a higher angle of repose
excess water eliminates air spaces resulting in loss of surface tension and reduces friction between particles; thus, the angle of respose is
much lower
heavy rains or raising the water level in a reservoir can ?; caves are an exception
destabilize weakened rock slopes
caves are (less/more) stable when completely filled with water and why?
more; the water helps support the roof
a cave with a thin or weak roof may collapse when
the water level drops below the top of the cave
flooding
mass wasting causing flooding, and flooding causing mass wasting
examples of mass wasting causing flooding
Gros Ventre River, Wyoming, 1925; Vaiont Dam, Italy, 1963
liquefaction
liquefying saturated sediments by vibration (vibration is typically achieved by earthquakes)
? and ? are the most commonly susceptible to liquefaction during earthquakes
sands and silts
examples of liquefaction
1964 large earthquake in Alaska caused it in Alaska and Japan; 2004 earthquake in Japan
quick clay
unstable clay that can suddenly liquefy and flow
quick clay is formed when
marine clay with a high salt content is uplifted and leached by freshwater
example of quick clay
Rissa, Norway: a farmer dug a pit to extend a barn and placed the removed sediment near the edge of a lake, causing underlying clay to suddenly give way and flow like water into the lake; Canada over 250 known slides have been attributed to quick clays (one in 1908 in Quebec killed 33)
most quick clays are found in
northern countries once covered with continental glaciers
