World GeographyWorld Geography

Unit 1: Land and Water FormsUnit 1: Land and Water Forms

Wearing Down Landforms Wearing Down Landforms Wind and WavesWind and Waves

Erosion by SeaErosion by Sea

Wind ErosionWind Erosion

• Wind does not have the energy to erode or Wind does not have the energy to erode or transport large rock particles like water or transport large rock particles like water or glaciers.glaciers.

• It works mostly on sand and fine sedimentIt works mostly on sand and fine sediment• It’s effects are most commonly seen in It’s effects are most commonly seen in

deserts and on beachesdeserts and on beaches• Works in two main waysWorks in two main ways

– DeflationDeflation– AbrasionAbrasion

DeflationDeflation

• Deflation: The hollowing of a piece of Deflation: The hollowing of a piece of land by wind removing small particles.land by wind removing small particles.

• Deflated landscapes appear as jagged Deflated landscapes appear as jagged deserts, with bare and exposed deserts, with bare and exposed bedrock or a dense pavement of bedrock or a dense pavement of stones and gravelstones and gravel

• A desert with these features is known A desert with these features is known as a hamadaas a hamada

AbrasionAbrasion

• Abrasion: When wind-borne particles Abrasion: When wind-borne particles blow against a surface, sandblasting blow against a surface, sandblasting and wearing them away.and wearing them away.

Wind DepositionWind Deposition

• Wind may carry particles for Wind may carry particles for thousands of kilometers, but they thousands of kilometers, but they must come downmust come down

• Eventually particles are deposited in Eventually particles are deposited in a particular type of desert known as a particular type of desert known as an ergan erg

• Erg: areas of extensive dunes, Erg: areas of extensive dunes, mounds, and ridges of sandmounds, and ridges of sand

ErgsErgs

• The greatest erg desert is the Sahara The greatest erg desert is the Sahara DesertDesert

• The most common landscape features of The most common landscape features of an erg are sand dunes.an erg are sand dunes.

• Sand Dunes: Cresent or triangular shaped Sand Dunes: Cresent or triangular shaped piles of sand that form when slowing wind piles of sand that form when slowing wind drops particles of sanddrops particles of sand

• Barchan – Crescent shaped dune, with Barchan – Crescent shaped dune, with horns pointing into the windhorns pointing into the wind

Wave ErosionWave Erosion

• As wind passes over water it As wind passes over water it transfers energy through frictiontransfers energy through friction

• This transfer of energy creates wavesThis transfer of energy creates waves

• Where waves meet land erosion Where waves meet land erosion occursoccurs

Wave Movement and Wave Movement and DirectionDirection

• To understand wave erosion you To understand wave erosion you must understand two important must understand two important conceptsconcepts

– Wave RefractionWave Refraction– Longshore DriftLongshore Drift

Wave RefractionWave Refraction

• Waves generally form in long ridges that are Waves generally form in long ridges that are perpendicular, at 90perpendicular, at 90oo’s, to the winds direction.’s, to the winds direction.

• As waves approach the shore they bend to line As waves approach the shore they bend to line up parallel to the shoreline.up parallel to the shoreline.

• The refraction occurs because as the waves enter The refraction occurs because as the waves enter the shallow water near the shore they loose the shallow water near the shore they loose energy.energy.

• As a result of wave refraction all of the energy As a result of wave refraction all of the energy from the wave is concentrated on the headlandfrom the wave is concentrated on the headland

• Headland: portions of land that reach out into the Headland: portions of land that reach out into the oceanocean

Longshore DriftLongshore Drift

• As waves move along a coast they As waves move along a coast they move eroded sand and gravel along move eroded sand and gravel along the shoreline.the shoreline.

• Longshore drift occurs because the Longshore drift occurs because the waves hit the coast at angles, waves hit the coast at angles, pushing the sediment along the pushing the sediment along the shore.shore.

SpitSpit

• Spit: A ridge of sand running away Spit: A ridge of sand running away from the coast, usually with a curved from the coast, usually with a curved seaward end. Spits grow in the seaward end. Spits grow in the prevailing direction of longshore drift. prevailing direction of longshore drift. Their ends are curved by the action Their ends are curved by the action of waves coming from different of waves coming from different directionsdirections

Water LandformsWater Landforms

• Sea Cave: A large, natural hollow in a Sea Cave: A large, natural hollow in a headland caused by wave erosionheadland caused by wave erosion

• Sea Arch: The feature which results Sea Arch: The feature which results when two caves occuring on either side when two caves occuring on either side of a headland are cut until they meet.of a headland are cut until they meet.

• Stack: An isolated islet or piller of rock Stack: An isolated islet or piller of rock standing up from the sea bed close to standing up from the sea bed close to the shore.the shore.

Sea CaveSea Cave

Sea ArchSea Arch

Sea StackSea Stack

How Water Landforms Are How Water Landforms Are CreatedCreated1.1. Water wears away at a headland Water wears away at a headland

forming sea caves on two sides.forming sea caves on two sides.

2.2. When the Caves meet they form an When the Caves meet they form an arch.arch.

3.3. When an arch collapses it forms a When an arch collapses it forms a Stack.Stack.

http://www.youtube.com/watch?v=5tU_g-sGFJI&feature=related

The Straightening Out of The Straightening Out of Irregular CoastlinesIrregular Coastlines

• Depends on how coast was formed.Depends on how coast was formed.– Glaciation and reboundGlaciation and rebound– Decreasing sea levelDecreasing sea level– Sea level rises or plates cause seafloor Sea level rises or plates cause seafloor

to sinkto sink

Embayed ShorelineEmbayed Shoreline

• Drowned or submerged coastline.Drowned or submerged coastline.– Sea level rises.Sea level rises.– Often through plate movementOften through plate movement– What were once river valleys submerge What were once river valleys submerge

making irregular coastline.making irregular coastline.– Erosion works quickly on this new land Erosion works quickly on this new land

and straightens it out.and straightens it out.

Clift and Terrace (emergent Clift and Terrace (emergent coastline)coastline)

• Result of rising land levelsResult of rising land levels

• As ice melts a great weight is lifted As ice melts a great weight is lifted off of the land causing it to reboundoff of the land causing it to rebound

• This occurs slowly, and is still This occurs slowly, and is still happening.happening.

Emergent CoastlineEmergent Coastline