By Wind and WavesBy Wind and Waves

Review

•Any natural process that removes sediments and carries them away from one place to another is called erosion.

•Gravity is the driving force behind all erosion.

•Everything on earth is constantly being pulled toward the earth’s center by gravity.

•Any particle of matter that is free to move is going to move downward due to gravity unless some other force interferes.

Wind Erosion• Wind erodes dry land much more

effectively than it does moist land (more plants with roots to hold the soil).

• As the wind erodes land it carries rock particles along with it, mostly sand, silt, and clay.

• Sand material is moved along by a number of jumps and bounces, much how a pebble is moved along the bottom of a stream bed.

• The wind causes friction on sand grains to lift them into the air. Gravity pulls them down to the surface.

• Sand grains, which cause most of the abrasion, do not rise higher than about 1 meter, and they move in the same direction the wind is blowing.

• Dust particles (silt and clay) can be carried along great distances and at greater heights than sand particles.

Effects of wind erosion

• Abrasion is the weathering of rock particles by the impact of other rock particles.

• In areas where there are strong, steady winds, large amounts of loose sand, and relatively soft rocks, abrasion causes a great amount of erosion.

• Pebbles and small stones exposed to wind abrasion show surfaces that are flattened and polished on two or three sides.

• Rocks smoothed this way are called ventifacts.

• Particles that have been moved by the wind are well rounded by the repeated impact of grain against grain, and when examined with a magnifier, their surfaces have a frosted appearance.

• Outcrops of rocks in arid regions undergo the greatest amount of erosion close to their base, because particles transported by the wind remain close to the ground.

DEFLATION DEFLATION

Removal of fine particles by wind leaves hollows behind (Deflation Hollows)

Also leaves a surface of closely packed Also leaves a surface of closely packed stones (DESERT PAVEMENT)stones (DESERT PAVEMENT)

SAND DUNESSAND DUNESare ridges of wind are ridges of wind deposited sanddeposited sand

- Usually 3 to 15 - Usually 3 to 15 metres high, but can metres high, but can reach 180 metresreach 180 metres

- - A continuously A continuously changing dune is changing dune is ACTIVEACTIVE Corbis Digital StockCorbis Digital Stock

The formation of The formation of dunes depends on:dunes depends on:

- amount of sand- amount of sand- speed and - speed and direction of winddirection of wind- occurrence of - occurrence of vegetationvegetation

Corbis Digital StockCorbis Digital Stock

wind directionwind direction

BACKSLOPEBACKSLOPE SLIPFACESLIPFACE

movement of sand

movement of sandangle of angle of reposerepose

crestcrest

TYPES OF SAND DUNETYPES OF SAND DUNE1.) BARCHAN1.) BARCHAN- most common type- most common type- crescent-shaped- crescent-shaped

Wind directionWind direction

backslopebackslope

slip faceslip face

2.) TRANSVERSE DUNES2.) TRANSVERSE DUNES• low sand ridge at right angles to the wind low sand ridge at right angles to the wind directiondirection• may form because of large amounts of sandmay form because of large amounts of sand

windwind

3.) LONGITUDINAL DUNES3.) LONGITUDINAL DUNES

• low sand ridges parallel to the wind directionlow sand ridges parallel to the wind direction• may form because of a limited amount of sandmay form because of a limited amount of sand• also known as also known as seifseif dunes dunes

windwind

LOESS• Finely

textured sediment (silt) wind-blown long distances

• Wind-blown glacial debris formed large deposits

Wave Erosion and Deposition

• Energy from waves transfers to land and causes erosion to form erosional features such as cliffs.

• Sand is the product of this erosion. The type of sand depends on the material being eroded (typically quartz and coral—white sand, or basalt—black sand).

• Sand material is transported by waves and currents to form beaches and other transient coastal landforms.

wave lengthwave length

wave wave heightheight

crestcrest

troughtrough

particles in particles in waves follow a waves follow a circular patterncircular pattern

WAVESWAVES

At the shoreline

• Water becomes shallow, wave height increases because wave length decreases

• Waves become steeper, then collapse (breakers)

• Surf - sequence of breaking waves

• Swash - water sliding up beach

• Backwash - water flowing back down beach to sea

Wave refraction BayBay

HeadlandHeadland

• Waves arriving at bays are slow (deposition)• At headlands, faster (erosion)

• A sequence of features is produced as headlands are degraded

• Sea cliffs• Waves erode base

-undercutting the cliff the cliff retreatsretreats

• Also produces Also produces sea cavessea caves

• As cliffs retreat As cliffs retreat produces a produces a wave-wave-cutcut platform platform

• Headlands Headlands may be may be erodederoded back leaving a back leaving a remnant (remnant (stackstack))

stackstack

Longshore drift

• Waves arrive at a coast at an angle (swash)

• Backwash returns at 90

degrees

Sand is moved along the beach = Sand is moved along the beach = longshore longshore drift or longshore currentdrift or longshore current

Coastal deposition

• Result of longshore drift and a lot of sediment

• produces extensions of deposit from the shoreline

• May grow across a bay (baymouth bar or barrier beach)

• May link an island to the main land (tombolo)

spit = curved extensionspit = curved extension

Sandbar •Off-shore sand deposit that lies just below the water surface

Barrier Island Coasts

• Occur on low lying coasts with gentle gradients

• BARRIER ISLANDS - low ridges of sand built by waves– behind the islands are lagoons

– shallow water with tidal deposits

• TIDAL INLETS - gaps between the islands