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

Wind and Wind and Wave ErosionWave Erosion

……and a teeny little bit about and a teeny little bit about mass movementmass movement

What is EROSION?What is EROSION?The removal and transport of materials The removal and transport of materials

by natural agents such as wind, by natural agents such as wind, water and ice.water and ice.

WIND EROSIONWIND EROSION

Sediment Sediment SizesSizes

SandSand A sediment size…not A sediment size…not

a compositiona composition 2mm 2mm 0.06mm 0.06mm Gritty feelGritty feel Can be composed of Can be composed of

anythinganything!! Not very cohesiveNot very cohesive

Sediment SizesSediment Sizes SiltSilt Smaller than Smaller than

sandsand 0.06 mm 0.06 mm

0.003mm0.003mm Fine like powder Fine like powder

Sediment SizesSediment Sizes ClayClay < 0.003 mm < 0.003 mm Smallest Smallest

sediment sizesediment size Very cohesiveVery cohesive

DeflationDeflation Most Most

common common form of wind form of wind erosionerosion

The removal The removal and and transport of transport of siltsilt

Wind ErosionWind Erosion

Dust Bowl

Kansas (1996)

Deflation and Deflation and desert desert pavementpavement

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

Wind ErosionWind Erosion Saltation- bouncing of Saltation- bouncing of

sand grains (wind lifting sand grains (wind lifting then dropping)then dropping)

http://www.nps.gov/grsa/resources/saltation.htmhttp://www.nps.gov/grsa/resources/saltation.htm

WAVE EROSIONWAVE EROSION

What causes waves?What causes waves?

Why do waves “break”?Why do waves “break”? Waves approach shoreline smoothly Waves approach shoreline smoothly

until they reach shallow water.until they reach shallow water. As waves scrapes the bottom, the As waves scrapes the bottom, the

lower part slows down and the upper lower part slows down and the upper part moves ahead…part moves ahead…

The crest falls over and breaks onto The crest falls over and breaks onto the surfthe surf

Longshore driftLongshore drift Water and sediment are transported in a zig-Water and sediment are transported in a zig-

zag pattern as longshore currents and waves zag pattern as longshore currents and waves approach the shoreline at an angle. approach the shoreline at an angle.

This zig-zag pattern is the mechanism for This zig-zag pattern is the mechanism for sediment transport as the sediment transport as the swashswash is is immediately followed by the immediately followed by the backwashbackwash to the to the ocean. ocean.

This energy created from the breaking waves This energy created from the breaking waves allows for weak currents to carry large allows for weak currents to carry large amounts of coarse-grained sediment down the amounts of coarse-grained sediment down the shoreline.shoreline.

Current + wave motion= Current + wave motion= longshore driftlongshore drift

Another look at it…Another look at it…

One more look…One more look…

Carefully examine the photo. Carefully examine the photo. Which direction is the long shore Which direction is the long shore

current coming from?current coming from?

Answer: Answer: WestWest

Longshorecurrent

Mass Movement Mass Movement (aka Mass (aka Mass Wasting)Wasting)

landslide

rockfall

creep

creepslump

mudslide

What is MASS MOVEMENT?What is MASS MOVEMENT?The term refers to downward transportation of The term refers to downward transportation of

weathered materials by gravityweathered materials by gravity

slow rapidCreep-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 MovementsTriggers of Mass Movements Heavy rainHeavy rain Spring ThawsSpring Thaws Volcanic EruptionsVolcanic Eruptions EarthquakesEarthquakes

MOST COMMON?...heavy rainsMOST COMMON?...heavy rains