wind and waves (earth science)

Wind and

WavesPrepared by:Abegail R.T.

(Earth Science)

Wind Movement of the gases in

the air. When air heats up, it

expands and as a result, it rises. But when air rises, it doesn’t just leave a big hole behind with no air in it.

Coolen air from the surrounding rushes into replace it and that is what we call wind.

Cold air can sometimes slide across the top of warm air too which creates a very unstable situation and usually results in storms.

WaveWaves are the result of

wind traveling over water. The waves arise from the surface tension of water.

Waves are form of energy which in the case of ocean waves, lifts water up as it moves along. Behind the wave it falls and rises again a few times which is why you get more than one ripple from a stone falling into a fond.

Winds erode by deflation and abrasion. Deflation is the blowing away of fine dry material until the water table is reached.

The moisture of the water table binds the material together so it is generally understood that this represents the base level of wind erosion.

Wind Erosion

The wind can create landforms when it deposits its sediments, especially in desserts and along coasts. Both layers of loess and sand dunes are landscape features deposited by wind. These blankets of silt and mounds of sand are striking features in some parts of the world.

Wind Deposits

Windblown silt that blankets the landscape. Dust storms over thousands of years picked up this material transported it, and then deposited it.

The thickest and most extensive deposits of loess on Earth in Western and Northern China. The silt was derived from nearby deserts. This fine, buff – colored sediment gives the yellow riven its name.

Loess

Which are hills of windblown soil. Dunes are formed where there is a supply of dry, unprotected soil and wind strong enough to move it.

Dunes

The crescent – shape of dunes, these are most common where there is limited supply of sand.

Barchans

The principal erosional work of the wind is to transport rock material. However, the wind is also able to break down unweathered rock. The wind abrades solid rock by means of the rock particles it carries.

Along beaches, or on other dry sandy surfaces. They develop one or more smooth polished faces as a result of wind abrasion. Such pebbles are called ventifacts (from latin ventus, meaning “wind”)

Various land forms such as natural bridges, rock pinnacles, rocks perched on pedestals, and even larage desert basins have been attributed to abrasion by wind – driven sand.

Wind – caused abrasion

Erosion by the sea

When waves reach the shore much of their energy is spent in eroded the rock of the coast. How rapidly rocks are worn back depends upon the nature of the rock material.

Currents created wave action also play a part in shore erosion.

The attack on the shore

Move toward the sea along the bottom, close to the shore.

The undertow tends to move rock debris out to sea along the bottom. However, the force of the waves rushing against the shore is stronger that the undertow.

1. Undertow currents

Cause of waves which strike the shore at an angle move parallel to the shoreline.

Longshore currents are common and tend to move loose material along the coast.

2. Longshore Currents

When water is flung against the shore it can wash away loose sediment such as sand, volcanic ash, and glacial till.

As in the case of streams, glaciers, and wind, waves acquire cutting tools in the form of rock fragments.

Erosion due to wave cutting

Terrace extends out beneath the water at the cliff base.

Wave cut terrace

Building an extension to the wave – cut terrace, the finest particles, however, are often scattered widely over the sea floor by currents.

Wave built terrace

Wave action carries rock materials up on the shore. These deposits are beaches. They may consist of sand, pebbles, cobbles, or boulders, or mixtures of these materials.

Shore Deposits

1. Wave action – tend to deposit debris on the shore.

2. Undertow and Longshore – tend to remove the debris on the shore.

Beaches are affected by two opposing processes:

A wide shelf of deposits may be up beneath the water just offshore resulting gentle slope of the sea away from the shore then causes wave to form a low sand bar.

Offshore Bar

Water between bar and the mainland.

Lagoon

Formed on a headland on Island near the mouth of a bay or inlet by offshore currents moving parallel to the shore.

Split

Coral reefs commonly form characteristic

shoreline features in tropical and subtropical

waters. Corals belong to one of

the simpler groups of animals, the

coelenterates. The typical coral reef

consists of great numbers of such

colonies together with many other kinds of animals and plants.

Coral Reefs

1. Fringing Reef – is closely attached the shore of an Island or continent.

2. Barrier Reef – is a long narrow strip some distance from the shore.

3. Atoll – is a roughly circular reef where encloses a lagoon.

3 Forms of Coral Reefs

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