Wind and Wave Erosion …and a teeny little bit about mass movement

What is EROSION? The removal and transport of materials by natural agents such as wind, water and ice.

WIND EROSION

Sediment Sizes Sand Sand A sediment size…not a composition A sediment size…not a composition 2mm  0.06mm 2mm  0.06mm Gritty feel Gritty feel Can be composed of anything! Can be composed of anything! Not very cohesive Not very cohesive

Sediment Sizes Silt Silt Smaller than sand Smaller than sand 0.06 mm  0.003mm 0.06 mm  0.003mm Fine like powder Fine like powder

Sediment Sizes Clay Clay < mm < mm Smallest sediment size Smallest sediment size Very cohesive Very cohesive

Deflation Most common form of wind erosion Most common form of wind erosion The removal and transport of silt The removal and transport of silt Wind Erosion

Dust Bowl

Kansas (1996)

Deflation and desert pavement During this process wind removes the top layer of fine, dry rock/soil wind removes the top layer of fine, dry rock/soil fragments too large for the wind to carry are left behind fragments too large for the wind to carry are left behind These remaining fragments form a surface of closely packed rocks called desert pavement. These remaining fragments form a surface of closely packed rocks called desert pavement.

Wind Erosion Saltation- bouncing of sand grains (wind lifting then dropping) Saltation- bouncing of sand grains (wind lifting then dropping)

WAVE EROSION

What causes waves?

Why do waves “break”? Waves approach shoreline smoothly until they reach shallow water. Waves approach shoreline smoothly until they reach shallow water. As waves scrapes the bottom, the lower part slows down and the upper part moves ahead… As waves scrapes the bottom, the lower part slows down and the upper part moves ahead… The crest falls over and breaks onto the surf The crest falls over and breaks onto the surf

Longshore drift Water and sediment are transported in a zig-zag pattern as longshore currents and waves approach the shoreline at an angle. Water and sediment are transported in a zig-zag pattern as longshore currents and waves approach the shoreline at an angle. This zig-zag pattern is the mechanism for sediment transport as the swash is immediately followed by the backwash to the ocean. This zig-zag pattern is the mechanism for sediment transport as the swash is immediately followed by the backwash to the ocean. This energy created from the breaking waves allows for weak currents to carry large amounts of coarse-grained sediment down the shoreline. This energy created from the breaking waves allows for weak currents to carry large amounts of coarse-grained sediment down the shoreline.

Current + wave motion= longshore drift

Another look at it…

One more look…

Carefully examine the photo. Which direction is the long shore current coming from?

Answer: West Longshore current

Mass Movement (aka Mass Wasting) landslide rockfall creep slump mudslide

What is MASS MOVEMENT? The term refers to downward transportation of weathered materials by gravity slowrapid Creep-imperceptibly slow (trees, fences) Rockfall- Solifluction-dependent upon cycles of freezing (similar to basal slip Landslide-masses of loose rock/sediment Mudflow-dry, mountainous regions with sudden, heavy rain; also volcanic activity (lahars) Slump-loose soil slips downslope as one “piece”

Triggers of Mass Movements Heavy rain Heavy rain Spring Thaws Spring Thaws Volcanic Eruptions Volcanic Eruptions Earthquakes Earthquakes MOST COMMON?...heavy rains MOST COMMON?...heavy rains