By 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 Removal of fine particles by wind leaves hollows behind (Deflation Hollows) Also leaves a surface of closely packed stones (DESERT PAVEMENT)

SAND DUNES are ridges of wind deposited sand - Usually 3 to 15 metres high, but can reach 180 metres - A continuously changing dune is ACTIVE Corbis Digital Stock

The formation of dunes depends on: - amount of sand - speed and direction of wind - occurrence of vegetation Corbis Digital Stock

wind direction BACKSLOPE SLIPFACE movement of sand angle of repose crest

TYPES OF SAND DUNE 1.) BARCHAN - most common type - crescent-shaped Wind direction backslope slip face

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

3.) LONGITUDINAL DUNES low sand ridges parallel to the wind direction low sand ridges parallel to the wind direction may form because of a limited amount of sand may form because of a limited amount of sand also known as seif dunes also known as seif dunes wind

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 length wave height crest trough particles in waves follow a circular pattern WAVES

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 refractionBay Headland

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 retreats

Also produces sea caves Also produces sea caves As cliffs retreat produces a wave- cut platform As cliffs retreat produces a wave- cut platform

Headlands may be eroded back leaving a remnant (stack) Headlands may be eroded back leaving a remnant (stack) stack

Longshore drift Waves arrive at a coast at an angle (swash) Backwash returns at 90 degrees Sand is moved along the beach = longshore drift 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 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