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