Announcements

1
Announcements

• Kayaking Field Trip
• Show up at 1230 pm
• More can come if paid by 5 pm today
• Defenses
• Due by 5 pm today

2
Plan for Today

• Define Mass Wasting
• Understand why slopes dont slide/fall/flow
• Types of mass wasting
• Causes of mass wasting

3
Mass Wasting

• Definition Erosion without (much, if any)
  transporting agent i.e., (wind/water/ice)

4
Why dont slopes fail

• What keeps the top of Sehome Hill up there,
  instead of down here?
• Rock Integrity
• Friction

5
Important types of mass wasting

• Slide Rock stays coherent, more or less
• Fall Rocks fall
• Flow Rocks behave like a fluid

6
Slump (a type of slide)

• Indicators
• Scarp
• Hummocky terrain on and below (earthflow)

7
Slump

• Earth moves on shallow, curved fault

8
(No Transcript)
9
(No Transcript)
10
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

11
(No Transcript)
12
Debris Flow
13
Rockslide

• Rock moves because theres nothing holding it
  back!
• Generally requires a pre-existing low-friction
  surface...

14
Rockslide

• like a clay layer, once its wet...

15
Earthquake Lake, MT

• 28 deaths in 1959, triggered by earthquake

16
Earthflow

• basically a very viscous (thick) debris flow
• slow-moving
• faster in wetter weather

17
Earthflow
18
Creep

• very slow
• result of freezing and thawing

19
Creep
20
sandstone
shale
21
Creep
22
Factors in mass wasting

• steepness
• wetness
• decreases friction by increasing pore pressure
• soil weight
• water increases soil weight
• vegetation
• deep roots anchor soil

23
Triggers for rapid Mass Wasting

• Rain
• Oversteepening
• cutting at foot of slope
• piling on head of slope
• Deforesting / Devegetating
• Earthquakes

24
a-debris flow b-rock fall c-earthflow d-slump
25
a-debris flow b-rock fall c-earthflow d-slump
26
a-debris flow b-rock fall c-earthflow d-slump
27
a-debris flow b-rock fall c-earthflow d-slump
28
Check out the mass wasting links

• Links to Washington landslide stories
• Bainbridge Island story in the Atlantic Monthly
• Kelso and the mobile subdivision

29
Mass Wasting WarmUp your dream house

• I would avoid buying a house on a cliff which
  obviously is in the process of being eroded by
  the water beneath it. This happens in California
  all the time...then people complain when their
  million dollar house falls into the ocean!
  Anybody can see the bloody hill is being washed
  away!
• To ensure that I wouldn't buy property with a
  slope stability problem I would look for an area
  that had trees to solidify the ground with roots,
  and some sort of solid material underneath the
  soil like granite, instead of material that could
  slide like clay.

30
Mass Wasting WarmUp your dream house

• I would look at the ground to try and find
  evidence of a geologically recent landslide.