Mass Movement Variables
•  Material’s weight
–  Gravity
•  Material’s resistance to sliding or
flowing
•  Trigger
–  Earthquake (shakes material loose)
•  Water
Water and Sand
•  Dry Sand (Lots of Friction)
– Prevent sediment from holding together
Water and Sand
•  Saturated Sand (Least Friction)
–  Water completely surrounds grains
Types of Movement
•  Creep
–  Slow, steady, downhill flow of loose,
weathered materials
–  Few cm a year
Types of Movement
•  Flows
–  Materials flows as if they were thick liquid
–  Few cm a year or rapidly
•  Mudflows
1998 Sarno Italy 135 dead
Mudflows
•  Swiftly moving mixtures of mud and
water
•  Can be triggered by earthquakes
•  Common in volcanic regions
–  Heat melts snow on slopes and the water
saturates the sediment and flows down
Slides
•  Landslides - Rapid,
downslope
movement of
materials when thin
block of loose soil,
rock, and debris
separates from
underlying bedrock
Slumps
•  Materials in a
landslide
rotate and
slide along a
curved surface
•  Thick soils
•  Moderate to
steep slope
Rock Falls
•  Commonly occur at
high elevations, in
steep road cuts, and
rocky shorelines
•  Rocks are loosened by
physical weathering
–  Freezing and thawing
–  Plant growth
Avalanches
•  Landslides that occur in mountainous areas
with thick snow
•  Usually need 35˚
•  About 10,000 avalanches each year in
western US
•  Sun’s radiation will melt snow
–  Refreezes at night with an icy crust
–  Snow builds up then slips down slope=avalanche
Avalanches
Mass Movements and People
•  Human activities contribute to mass
movement
–  Heavy buildings
–  Roads
•  Avoid building structures on slopes >25˚
and unstable
•  Protective fences and nets by roads
Review
•  What is 1 fast and 1 slow mass
movement?
•  Why does mass movement occur?
•  How does water affect mass
movement?