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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.