Erosion and Deposition

How is erosion different than weathering? Weathering breaks rocks apart whereas erosion moves weathered particles from one place to another.

Deposition – when sediment is placed in a new location

Erosion

What are the agents of erosion? Water Wind Ice Gravity Erosion has been reshaping the Earth for

millions of years. Erosion can takes many years or happen

all of a sudden.

Deposition

Deposition occurs when the agent of erosion loses energy and can no longer carry the eroded particles.

Debris – the particles that have been moved.

Erosion and Deposition by Gravity

Erosion by gravity is called mass wasting. Rockfall – individual block of rock drops

suddenly and falls freely down a cliff or mountain.

Often caused by ice wedging. Talus slope – forms at the bottom of a cliff

or mountain which has been eroded.

Rockfall cat

Rockfall cat

Rockfall cat

Talus Slope cat

Erosion and Deposition by Gravity

Land slide – a large mass of rock moves as a unit down a slope.

Will leave a fan-shaped deposit of debris Can be triggered by:

an earthquake. Too steep a slope. Undercutting of the bottom of the slope.

Land Slide cat

Erosion and Deposition by Gravity

Mud flow – consists of a debris and a large amount of water.

Occurs in valleys after a heavy rainfall. Leaves a widespread layer of mud. Lahar - is a mud flow that occurs when a

volcano erupts melting the ice on the summit.

Lahars at Mt Saint Helens traveled 36 miles from the mountain

Mud Flow cat

Aftermath of Mud Flow cat

Lahar at Mt Saint Helens cat

Erosion and Deposition by Gravity

Slump – a curved section of debris move as a unit down a slope.

Caused by: Too steep a slope. Undercutting of the bottom of the slope. Too much added water

Slump cat

Erosion and Deposition by Gravity

Creep – the slowest form of mass movement.

The soil or debris moves at a rate of 1-10 mm per year.

Signs of creep: Row of headstones, telephone poles or fence

posts all leaning down hill. Bottom of tree trunks all bent.

Creep

Roots are planted deep in soil that is not affected by creep. The trunk of the tree is being pushed downslope by creep.