Mass Movement
Triggers of Mass Movement
Mass movement is the transfer of rock and soil downslope due to gravity
Factors that commonly trigger mass movements are:Saturation of surface materials with waterOversteepening of slopesRemoval of vegetationEarthquakes
Types of Mass Movements
Geologists classify mass movements based on the kind of material that moves, how it moves, and the speed of movement
Six types of mass movement include:Rock fallsSlidesSlumpsMudflowsEarthflowsCreep
Rock FallsWhat moves: A rockfall occurs when rocks
or rocks fragments fall freely through the airHow it moves: Slopes that are too steep to
hold loose material on the surfaceSpeed of movement: Any speedOther: Result from frost action, triggers
other mass movements
SlidesWhat moves: A block of material moves
suddenly along a flat, inclined surface How it moves: Occurs on high mountain
areasSpeed of movement: FastOther: Triggered by rain or melting snow
Slumps
What moves: The downward movement of a block of material along a curved surface
How it moves: Upper part tilts back, leaving a crescent-shaped cliff
Speed of movement: Slow over a short distance
Other: Triggered by heavy rain
Slump
MudflowWhat moves: A mixture of soil, rock, and
water that has a consistency of wet concrete moves downslope
How it moves: Heavy downpour will cause flows
Speed of movement: QuicklyOther: Very dangerous in populated areas
Earthflows
What moves: The downslope movement of water-saturated, clay-rich sediment
How it moves: Occurs on hillsides in humid regions
Speed of movement: Slow
CreepWhat moves: The downhill movement of soil
and regolithHow it moves: Freeze-thaw cyclesSpeed of movement: Extremely slowOther: Can move fences, crack walls and
underground pipes