Wind Erosion Ch. 8 Section 3

Wind Erosion When air moves, it picks up loose materials and transports it to other places.  Air differs from other erosional forces because it cannot pick up heavy sediments.  Wind carries and deposits sediments over large areas.  When wind erodes by deflation it blows across loose sediments and removes small particles such as silt and sand.

Wind Erosion The heavier material is left behind. When windblown sediment strikes rock, the surface of the rock gets scraped and worn away by the process called abrasion Abrasion is similar to sandblasting , as sand grains strike against rock and break off small pieces. The rocks get worn down gradually. Deflation and abrasion occur mostly in deserts beaches and plowed fields, which have fewer plants to hold sediment in place

Abrasion at Work

Abrasion Again!!

Wind Erosion Sandstorms occur when the wind blows strongly in sandy parts of deserts and sand grains form a low cloud just above the ground.  When soil dries out, particles of silt and clay can be carried by the wind in dust storms. These storms blow topsoil from fields and places where vegetation has disappeared.

THE DUST BOWL

Wind way is the dune moving?

Wind Erosion Wind erosion is common where there are no plants to protect the soil.  One of the best ways to stop wind erosion is to plant vegetation.  Farmers have planted trees to act as windbreakers that prevent soil erosion. 

Wind Erosion As the wind hits the trees, its energy of motion is reduced, and it is no longer able to lift particles. Windbreaks also trap snow and hold it on land, which increases the moisture level of the soil. Plants with fibrous Root systems, such as grasses, twist and turn between particles in the soil and hold it in place.

Wind breaks!

Deposition by Wind Sediment blown by wind are eventually deposited.  Over time, these deposits develop into landforms  Wind deposits of fine-grained sediments known as loess are found near the Mississippi and Missouri Rivers.  This sediment was blown from glacial outwash areas and then settled on hilltops and in valleys.

Loess

Deposition by Wind A dune is a mound of sediment drifted by the wind. The particles packed together in a thick, unlayered yellow-brown deposit that is as fine as talcum powder. A dune is a mound of sediment drifted by the wind.  Dunes form when sand begins to build up behind an obstacle, and more and more material becomes trapped.

Deposition by Wind A sand dune has 2 sides. The side facing the wind has a gentle slope, the side away from the wind is steeper. Unless they are planted with grasses, most dunes migrate away from the direction of the wind. As dunes lose sand on one side, they build it up on the other.

Deposition by Wind The shape of a dune depends on the amount of sand or other sediment available, the wind speed and direction, and the amount of vegetation present.  Erosion and deposition are part of a cycle that constantly shapes the land.

Sand Dune