Chapter 17

The Process of Wind Erosion

• Saltation is the skipping and bouncing movement of sand or other sediments, caused by wind or water.• Moving sand grains knock into one another,

bounce up into the air, fall forward, and strike other sand grains, causing them to roll and bounce forward.

Section 2 Wind Erosion and Deposition

Chapter 17

• Deflation is a form of wind erosion in which fine, dry soil particles are blown away, removing the top layer of fine sediment or soil and leaving behind rock fragments that are too heavy to be lifted by the wind.

• Deflation may cause desert pavement, which is a surface consisting of pebbles and small broken rock.

• Scooped-out depressions in the landscape are called deflation hollows.

Section 2 Wind Erosion and Deposition

The Process of Wind Erosion, continued

Chapter 17

• Abrasion is the grinding and wearing away of rock surfaces through the mechanical action of other rock or sand particles.

• Abrasion commonly happens in areas where there are strong winds, loose sand, and soft rocks.

• The blowing of millions of sharp sand grains creates a sandblasting effect, helping erode, smooth, and polish rocks.

Section 2 Wind Erosion and Deposition

The Process of Wind Erosion, continued

Chapter 17

Wind-Deposited Materials

• Loess is a deposit of windblown, fine-grained sediment.

• Because wind can carry fine-grained material much higher and farther than it carries sand, loess deposits are often found far from their source.

Section 2 Wind Erosion and Deposition

Chapter 17

Loess

Section 2 Wind Erosion and Deposition

Chapter 17

• Dunes When the wind hits an obstacle, the wind slows down, depositing the heavier material. The material collects, creating an additional obstacle and eventually forming a mound that buries the original obstacle.

• The mounds of wind-deposited sand are called dunes. A dune moves as a result of the action of the wind.

Section 2 Wind Erosion and Deposition

Wind-Deposited Materials, continued

Chapter 17

• The Movement of Dunes Different wind conditions produce dunes in various shapes and sizes. A dune usually has a gently sloped side and a steeply sloped side, called a slip face.

Section 2 Wind Erosion and Deposition

Wind-Deposited Materials, continued

Chapter 17

Angle of Repose

• Gravity is an agent of erosion and deposition. It influences the movement of water and ice, and it causes rocks and soil to move downslope.

• Mass movement is the movement of any material, such as rock, soil, or snow, down a slope.

Section 4 Effect of Gravity on Erosion and Deposition

Chapter 17

• Material such as rock, soil, or snow moves downhill until the slope becomes stable. The angle of repose is the steepest angle at which loose material will not slide downslope.

• The angle of repose varies with the type of surface material. Characteristics such as size, weight, shape, and moisture level determine the angle of repose.

Section 4 Effect of Gravity on Erosion and Deposition

Angle of Repose, continued

Chapter 17

Rapid Mass Movement

• Rock falls happen when loose rocks fall down a steep slope. The rocks can range in size from small fragments to large boulders.

• Mass movements, like rock falls, happen suddenly and rapidly, and can be very dangerous.

Section 4 Effect of Gravity on Erosion and Deposition

Chapter 17

• Landslides are sudden and rapid movements of a large amount of material downslope.

• The most common type of landslide is a slump. Slumping occurs when a block of material moves downslope over a curved surface.

Section 4 Effect of Gravity on Erosion and Deposition

Rapid Mass Movement, continued

Chapter 17

• Mudflows are rapid movements of large masses of mud. Mudflows happen when a large amount of water mixes with soil and rock. The water causes the slippery mass of mud to flow rapidly downslope.

• Mudflows commonly happen in mountainous regions when a long dry season is followed by heavy rains.

Section 4 Effect of Gravity on Erosion and Deposition

Rapid Mass Movement, continued

Chapter 17

• Lahars are mudflows caused by volcanic eruptions or heavy rains on volcanic ash. Lahars can travel at speeds grater than 80 km/h and can be as thick as cement.

• On volcanoes with snowy peaks, an eruption can suddenly melt a great amount of ice. Water from the ice liquefies the soil and volcanic ash to produce a hot mudflow that rushes downslope.

Section 4 Effect of Gravity on Erosion and Deposition

Rapid Mass Movement, continued

Chapter 17

Slow Mass Movement

• Creep is the slow mass movement of material downslope.

• Although rapid mass movements are visible and dramatic, slow mass movements happen gradually. Slow mass movements occur more frequently, and move more material than rapid mass movements do.

Section 4 Effect of Gravity on Erosion and Deposition

Chapter 17

Creep

Section 4 Effect of Gravity on Erosion and Deposition