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Plan for Today
Define Mass Wasting
Understand why slopes dont
slide/fall/flow Types of mass wasting
Causes of mass wasting
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Mass Wasting
Definition: Erosion without (much, ifany) transporting agent i.e.,
(wind/water/ice)
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Why dont slopes fail
What keeps the top of Sehome Hill upthere, instead of down here?
Rock Integrity Friction
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Important types of mass
wasting Slide: Rock stays coherent, more or less Fall: Rocks fall
Flow: Rocks behave like a fluid
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Slump Earth moves on shallow, curved fault
scarp
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Debris Flow
Also called mudflow, mudslide
Soil & regolith get saturated with water
and flow like liquid cement to soup consistency
moderate to very fast movement
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Debris Flow
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Rockslide like a claylayer, once its wet...
E t L MT
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Eart qua e La e, MT 28 deaths in 1959, triggered by
earthquake
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Earthflow
basically a very viscous (thick) debrisflow
slow-moving faster in wetter weather
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Earthflow
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Creep very slow
result of freezing and thawing
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Creep
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Creep
from D. Schwert, NDSU
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Factors in mass wasting steepness wetness
decreases friction by increasing pore
pressure
soil weight water increases soil weight
vegetation deep roots anchor soil
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Triggers for rapid Mass
Wasting Rain Oversteepening
cutting at foot of slope piling on head of slope
Deforesting / Devegetating
Earthquakes
d b i fl b k f ll thfl d l
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a-debris flow b-rock fall c-earthflow d-slump
d b i fl b k f ll thfl d l
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a-debris flow b-rock fall c-earthflow d-slump
a debris flo b rock fall c earthflo d sl mp
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a-debris flow b-rock fall c-earthflow d-slump
a debris flow b rock fall c earthflow d slump
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a-debris flow b-rock fall c-earthflow d-slump
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Check out the mass wasting
links Links to Washington landslide stories Bainbridge Island story in the Atlantic
Monthly Kelso and the mobile subdivision
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Mass Wasting WarmUp:your dream house
I would avoid buying a house on a cliff whichobviously is in the process of being eroded by thewater beneath it. This happens in California all thetime...then people complain when their million
dollar house falls into the ocean! Anybody can seethe bloody hill is being washed away!
To ensure that I wouldn't buy property with a slopestability problem I would look for an area that had
trees to solidify the ground with roots, and somesort of solid material underneath the soil likegranite, instead of material that could slide likeclay.
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Mass Wasting WarmUp:your dream house
I would look at the ground to try and findevidence of a geologically recent landslide.