Chapter 8, Section 3

Wind ErosionWind

ErosionOccurs when air picks up loose

material and transports it elsewhere.Usually can’t pick up heavy

sediments.Carries and deposits sediments

over large areas.

Wind ErosionTypes

of Wind Erosion

Deflation and AblationHappen to all land surfaces.Occur mostly in deserts, beaches,

and plowed fields.

Wind ErosionDeflation Occurs when wind blows across

loose sediment, removing small particles such as silt and sand and leaving heavier, coarser material behind.

Wind ErosionAbrasionOccurs when the surfaces of rocks

get scraped and worn away by windblown sediments that strike the rock.Causes rocks to become pitted and

gradually worn down.

Wind ErosionSandstormsOccur when strong winds cause

sand grains to hit other sand grains, causing multiple grains to rise in the air and form a low cloud just above the ground.Usually winds do not carry sand

grains higher than 0.5 m above the ground.

Most sandstorms occur in deserts.

Wind ErosionDust

StormsOccur when wind carries smaller

particles of soil into the air.Soil is composed mostly of silt and clay

sized particles which can be carried higher into the air than heavier sand grains.

But, because the particles stick together, a faster wind is needed to lift them into the air.

Wind can carry the particles long distances causing dust storms to cover hundreds of kilometers. In the 1930’s dust picked up in Kansas fell in

New England and the North Atlantic Ocean. Dust from the Sahara has been traced as far

away as the West Indies (6,000 km).

Reducing Wind ErosionWindbreaksPlanting vegetation to reduce wind

erosion.Reduces the energy of the wind.Traps snow, causing the moisture

of the surrounding soil to increase.

Reducing Wind ErosionRoots Plants with fibrous roots systems,

such as grasses, work best for anchoring soil.

Deposition by WindLoess Large deposits of windblown fine-

grained sediments.Form when large deposits of fine-

grained sediments are packed together creating a thick, unlayered, yellow-brown deposit.

Produce fertile soils.

Deposition by WindDunes A mound of sediments drifted by

the wind.Form when wind blows across an

obstacle and deposits sediment behind the obstacle where the energy is the lowest.

Common in deserts and along the shores of oceans, seas, and lakes.

If the area has prevailing winds, the sand dunes will grow.Some dunes are up to 100 m high.

Deposition by WindMoving

DunesThe shape of a dune indicates the

direction that the wind usually blows.Side facing the wind has a gentler

slope.Side away from the wind is steeper.

Most dunes migrate (or move) away from the direction of the wind.As the dunes loose sand on one side

they build it up on the other.

Deposition by WindDune

ShapeThe shape of a dune depends on:

the amount of sand or other sediment available

the wind speedthe wind directionthe amount of vegetation present

Deposition by WindDune

ShapeTypes of dune shapes:

Barchan dune Crescent-shape The open side of the dune faces the

direction the wind is blowing. Points of the crescent are directed

downwind. Forms on hard surface where the sand

supply is limited.

Deposition by WindDune

ShapeTypes of dune shapes:

Transverse dune Long direction of the dune is

perpendicular to the general direction of the wind.

Form in areas where sand is abundant.

Deposition by WindDune

ShapeTypes of dune shapes:

Star Dunes Form in areas where the wind blows from

several directions.