Erosion and Deposition 2014 Nags Head perilously close to the Atlantic Ocean

Remember EROSION moves weathered sediments from one location to another. Four agents (FORCES) of erosion: gravity, wind, running water, glaciers. All have 1 thing in common: they carry sediments only when they have enough energy of motion. http://www.brainpop.com/science/earthsystem/erosion/

Deposition - dropping of sediments. All agents of erosion drop their sediments when their energy of motion decreases.

Deposition by gravity: 25-foot-high boulder blocked Topanga Canyon Road and cut power lines near Malibu. 2005

*actually the force that affects the rate of all types of erosion 1. Gravity Can cause materials to move down slope Mass movement! *actually the force that affects the rate of all types of erosion

4 types of erosion by gravity Creep Slump Earthflow/mudflow Landslide/Rockslides

Creep – happens when sediments slowly creep downhill due to freezing and thawing.

Results in leaning poles, fences, tombstones bent trees, cracked roads, etc.

This picture shows a hillside that is slowly moving over the sidewalk This picture shows a hillside that is slowly moving over the sidewalk. You can see the entire sidewalk towards the back of the picture in the distance and then see the hillside in the front of the picture that is slowly covering the sidewalk reducing its width. It is very well possible that with time it could cover an entire portion of the sidewalk blocking a section of it. This also offers some visual evidence of the presence of creep. (photo taken at Western Washington University Bellingham, WA)

Slump Takes place on steep slopes as loose materials slip down as one large mass. Doesn’t travel very fast or far. Occurs because the material under the slumped material weakens.

Thistledown slump

Earthflow: Mudflow Dry areas have thick layers of dry sediments (due to weathering). When heavy rains occur, it mixes with the sediments to form a thick pasty substance. (think chocolate pudding consistency). Gravity causes it to slide downhill.

Mt St Helen 1980

Landslide/Rockslides Large blocks of rock break loose from steep slopes and fall quickly to the bottom. Occur in mountainous areas. Happens after heavy rains or during earthquakes. Oct 2009

March 1995 La Conchita landslide

2005 Mudslide La Conchita

All mass movements: Are more likely to happen where there is a steep slope. Depend on gravity.

Cause a change in the shape of the slope so it becomes less steep. Will occur more often after a heavy rain because water adds mass and makes the sediments slippery. Cause a change in the shape of the slope so it becomes less steep.