Waves and Wind

Chapter 8 Section 5

How Waves Form• Energy in waves comes from wind that blows across

the water’s surface• As wind contacts water, energy is transferred• Energy that water picks up from wind causes water

particles to move up and down as the wave goes by; the water particles don’t move forward

• Only energy moves forward through the wave• In deep water, a wave only affects the water near

the surface• In shallow water, the wave drags the bottom,

creating friction, and slowing down.• This friction and drop in speed causes the water to

begin to move forward

Erosion by Waves• Waves are the major force of erosion along

coasts• The energy in waves can break rock apart and

make small cracks larger• Waves can erode land by abrasion

(sandpaper)• Waves nearing shore gradually change

direction as parts of a wave begin to drag on the bottom

• Headland- part of the shore that stick out into the ocean and are slower to erode

Landforms Created by Wave Erosion• Waves erode the base of the land along a steep

coast• The softer the rock, the quicker the erosion• Sea cave- a hollow area in the rock eroded by

waves over time• Sea arch- forms when waves erode a layer of

softer rock that underlies a layer of harder rock• Sea Stack- a pillar of rock rising above the water

due to a collapsed sea arch

Deposits by Waves• Waves erode the land AND deposit sediment• As waves reach the shore, they drop sediment to

form a beach• Beach- an area of wave-washed sediment along a

coast• Most waves hit the shore at an angle causing some

of the sediment to move down the beach with the current

• Longshore drift- process in which beach sediment moves down the beach with the current

• Spit- a beach that projects like a finger out into the water formed by deposition due to longshore drift

How Wind Causes Erosion• The main way wind

causes erosion is by deflation- the process by which wind removes surface materials

• Blowout- a bowl-shaped hollow caused by deflation in a slightly depressed area

Deposits resulting from Wind Erosion• Wind erosion and deposition may form sand

dunes and loess deposits• Sand dunes result when wind meets an obstacle• Sand dunes are most often made of coarser

sediments carried by wind• Loess- fine, wind-deposited sediment often

deposited far from their source• Thick loess deposits create valuable farmland

Review• How do ocean waves form?

Ocean waves form when wind makes contact with ocean water and transfers some of its energy to the water.

• Describe two landforms created by wave erosion and two landforms created by wave deposition.Sea cave, wave-cut cliff, sea arch, sea stack; beach, spit, and barrier beach

• Describe how wind erodes the landWind erodes by deflation. When wind blows over the land, it picks up smaller sediment and bounces or rolls larger sediment over the ground.

• How do sand dunes and loess deposits form?Sand dunes form when wind carrying sediment strikes an obstacle, such as a boulder or clump of grass, which traps the windblown sediment. Loess deposits form when wind lays down fine sediment in layers.

• You visit a rocky headland by the ocean that has a sea arch and several sea stacks. How might this area change in the next 500 years?In 500 years, the headland may have eroded back, evening out the shore. Erosion by waves may also have caused the sea arch to collapse, creating more sea stacks.