Chapter 8, Section 3 Wind Erosion Wind Erosion Occurs 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 Erosion Types of Wind Erosion Deflation and Ablation Happen to all land surfaces. Occur mostly in deserts, beaches, and plowed fields. Wind Erosion Deflation Occurs when wind blows across loose sediment, removing small particles such as silt and sand and leaving heavier, coarser material behind. Wind Erosion Abrasion Occurs 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 Erosion Sandstorms Occur 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 Erosion Dust Storms Occur 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 Erosion Windbreaks Planting vegetation to reduce wind erosion. Reduces the energy of the wind. Traps snow, causing the moisture of the surrounding soil to increase. Reducing Wind Erosion Roots Plants with fibrous roots systems, such as grasses, work best for anchoring soil. Deposition by Wind Loess 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 Wind Dunes 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 Wind Moving Dunes The 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 Wind Dune Shape The shape of a dune depends on: the amount of sand or other sediment available the wind speed the wind direction the amount of vegetation present Deposition by Wind Dune Shape Types 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 Wind Dune Shape Types 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 Wind Dune Shape Types of dune shapes: Star Dunes Form in areas where the wind blows from several directions.