Wind ErosionWind Erosion

Ch. 8 Section 3Ch. 8 Section 3

Wind ErosionWind Erosion

►When air moves, it picks up loose materials When air moves, it picks up loose materials and transports it to other places. and transports it to other places. 

►Air differs from other erosional forces Air differs from other erosional forces because it cannot pick up heavy sediments.because it cannot pick up heavy sediments.

►   Wind carries and deposits sediments over Wind carries and deposits sediments over large areas. large areas. 

►When wind erodes by deflation it blows When wind erodes by deflation it blows across loose sediments and removes small across loose sediments and removes small particles such as silt and sand. particles such as silt and sand.

Wind ErosionWind Erosion

► The heavier material is left behind. The heavier material is left behind. ► When windblown sediment strikes rock, the surface When windblown sediment strikes rock, the surface

of the rock gets scraped and worn away by the of the rock gets scraped and worn away by the process called abrasionprocess called abrasion Abrasion is similar to sandblasting , as sand Abrasion is similar to sandblasting , as sand

grains strike against rock and break off small grains strike against rock and break off small pieces. The rocks get worn down gradually.pieces. The rocks get worn down gradually.

► Deflation and abrasion occur mostly in deserts Deflation and abrasion occur mostly in deserts beaches and plowed fields, which have fewer plants beaches and plowed fields, which have fewer plants to hold sediment in placeto hold sediment in place

Abrasion at WorkAbrasion at Work

Abrasion Again!!Abrasion Again!!

Wind ErosionWind Erosion

►Sandstorms occur when the wind Sandstorms occur when the wind blows strongly in sandy parts of blows strongly in sandy parts of deserts and sand grains form a low deserts and sand grains form a low cloud just above the ground. cloud just above the ground. 

►When soil dries out, particles of silt When soil dries out, particles of silt and clay can be carried by the wind in and clay can be carried by the wind in dust storms. These storms blow dust storms. These storms blow topsoil from fields and places where topsoil from fields and places where vegetation has disappeared.vegetation has disappeared.

THE DUST BOWLTHE DUST BOWL

Wind way is the dune Wind way is the dune moving?moving?

Wind ErosionWind Erosion►Wind erosion is common where there Wind erosion is common where there

are no plants to protect the soil. are no plants to protect the soil. ►One of the best ways to stop wind One of the best ways to stop wind

erosion is to plant vegetation. erosion is to plant vegetation. ►Farmers have planted trees to act as Farmers have planted trees to act as

windbreakers that prevent soil windbreakers that prevent soil erosion. erosion. 

Wind ErosionWind Erosion

As the wind hits the trees, its energy of As the wind hits the trees, its energy of motion is reduced, and it is no longer able motion is reduced, and it is no longer able to lift particles.to lift particles.

Windbreaks also trap snow and hold it on Windbreaks also trap snow and hold it on land, which increases the moisture level land, which increases the moisture level of the soil.of the soil.

►Plants with fibrous Root systems, such Plants with fibrous Root systems, such as grasses, twist and turn between as grasses, twist and turn between particles in the soil and hold it in place.particles in the soil and hold it in place.

Wind breaks!Wind breaks!

Deposition by WindDeposition by Wind►Sediment blown by wind are eventually Sediment blown by wind are eventually

deposited.deposited.►   Over time, these deposits develop into Over time, these deposits develop into

landforms landforms ►Wind deposits of fine-grained sediments Wind deposits of fine-grained sediments

known as loess are found near the known as loess are found near the Mississippi and Missouri Rivers.Mississippi and Missouri Rivers.

►   This sediment was blown from glacial This sediment was blown from glacial outwash areas and then settled on outwash areas and then settled on hilltops and in valleys.hilltops and in valleys.

LoessLoess

Deposition by WindDeposition by Wind

The particles packed together in a thick, The particles packed together in a thick, unlayered yellow-brown deposit that is as unlayered yellow-brown deposit that is as fine as talcum powder.fine as talcum powder.

►A dune is a mound of sediment drifted A dune is a mound of sediment drifted by the wind. by the wind.  Dunes form when sand begins to build up Dunes form when sand begins to build up

behind an obstacle, and more and more behind an obstacle, and more and more material becomes trapped.material becomes trapped.

Deposition by WindDeposition by Wind

►A sand dune has 2 sides. The side A sand dune has 2 sides. The side facing the wind has a gentle slope, the facing the wind has a gentle slope, the side away from the wind is steeper.side away from the wind is steeper. Unless they are planted with grasses, Unless they are planted with grasses,

most dunes migrate away from the most dunes migrate away from the direction of the wind.direction of the wind.

As dunes lose sand on one side, they build As dunes lose sand on one side, they build it up on the other.it up on the other.

Deposition by WindDeposition by Wind

The shape of a dune depends on the The shape of a dune depends on the amount of sand or other sediment amount of sand or other sediment available, the wind speed and direction, available, the wind speed and direction, and the amount of vegetation present. and the amount of vegetation present. 

►Erosion and deposition are part of a Erosion and deposition are part of a cycle that constantly shapes the land.cycle that constantly shapes the land.

Sand DuneSand Dune