Chapter 15: Mass Wasting
Landslide in Peru


Yngay & Ranrahirca, Peru 1970
Before
After
Mass Wasting

Definition:



Downslope movement of rock, regolith & soil
under the direct influence of gravity
Does not require transporting medium such as
water, wind or glacial ice
Importance:

Combined with streams to create wide stream
valleys
Controls & Triggers




Water
Oversteepened Slopes
Removal of vegetation
Earthquakes as
triggers
Frictioncontrolled
Frictionreduced
Role of Water

Central America, Hurricane Mitch, 1998
Removal of
Vegetation
Earthquakes as Triggers

Northridge, CA 1994
Classification of Mass Wasting

Type of Materials:



Soil & Regolith dominate = debris, mud or earth
used in description
Bedrock breaks loose = rock in description
Type of Motion:



Falls: material in freefall
Slides: fairly coherent, moves along a surface
Flows: moves as viscous fluid
Rock Fall
Rapid Mass Wasting
Slumps

e.g. Point Fermin, CA
Rockslides

1925, Gros Ventre rockslide
Debris Flows

Lahar: debris flow composed mostly of
volcanic materials
Earthflows
Slow Mass Wasting

Creep
Slow Mass Wasting

Solifluction
Submarine Landslides



Can be larger than those on land
Most spectacular are those on flanks of
submarine volcanoes (AKA seamounts)
Major destructive process of Hawaiian
islands


e.g. Volcanic center of O’ahu now under water
to the NE
Can cause large tsunamis