Erosion

An Examination of the Erosional Agents That Shape Our Land

Main Erosional AgentsThis slideshow explores the transportation

variances and depositional features of the four main erosional agents. Rivers Glaciers Wind Ocean Waves

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The ‘Jobs’ of the Agents

Each erosional agent will be examined in 4 ways: General information Erosion Transportation Deposition

River Basics – Energy and Velocity

How much stream erosion and how much sediment is transported depends on the energy of the river.The energy of a river depends on The gradient (slope) The rivers discharge Channel

characteristics

A braided river

River Features

Meanders form as the stream gradient lowers. The river travels laterally across the flood plain forming large bends. Bends may become cut off (oxbow lakes) during flooding.

Edge of flood plain

Meanders

Oxbow lakes

Erosional FeaturesRivers are one of the most pervasive erosional agents, creating dramatic structures through stream abrasion.

River Transportation

Rivers transport sediment in three different ways: Solution –

dissolved particles Suspension –

‘floating’ particles Bed Load –

bouncing & sliding particles

Depositional FeaturesDeltas form at the end of rivers/streams as energy drops and sediment settles out.

Sediment plumes

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Glacial BasicsA Glacier is a thick ice sheet (min. 50 m) that is always moving.Glaciers cover almost 10% of the Earth’s land surface, however they are located mostly in Antarctica and Greenland.Glaciers move about 2-5 m/day, but can move 10’s of m/day

Glacial Features Crevasses are large crack in the ice that can extend down 50 m. Icebergs form at the edge of the ice as the glacier meets the ocean – called calving.

2 Main Glacier Types

Continental – Found covering Greenland and Antarctica. Unconfined and large

Alpine – Found in mountain ranges and confined to mountain valleys

Erosional Features

As the glacier moves, sediment in the ice scrapes against the bedrock forming striations or groves.

Striations

Transportation

Glaciers transport sediment in two ways – by rivers in the ice and by material being carried or pushed by the glacier.

Rock flour gives the river a green milky appearance

Depositional Features Sediment pushed to the edges of the glacier are called moraines.

Terminal – at the end Lateral – to the side Medial – in the middle

Medial moraine

Lateral moraine

Depositional Features

Drumlins form as the glacier carves out the land.

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Direction of ice flow

Directio

n of ice flow

Wind Basics

Wind is the least powerful of the erosional agents.In order for wind to be most effective, the area must be dry and lacking in vegetation. Deserts are excellent examples of such areas.

Dust storms

Desert Features

While most individuals think of deserts as areas of sand dunes – only about 20% of deserts consist of sand. Most deserts are composed of desert pavement - a rocky, hard packed surface.

Deflation – forming Desert Pavement

deflation--removal of fine-grained material by the wind--has exposed loose gravels mostly pebbles and cobbles. This makes up the majority of the desert surface.

Transportation

Most sediment is moved in the form of sand dunes. Sand dunes migrate through the transportation of sand up the gentle upwind side and deposition on the steeper slipface, thus sand is constantly recycled.

DepositionFormation of Sand Dunes

Dunes are created when loose sand gathers together due to an obstructionThe type of dune that forms depends on Amount of wind Amount of sand Amount of

vegetation

Sand Dunes in the Rx Record

The slipface of the sand dune can be preserved in the layers of rock

From this To this

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Types of Dunes

Wave Basics

Energy from waves is generated by the wind.How much energy depends on Strength of wind Time of blowing Fetch – area the

wind blows over

Wave Erosion

Oceans erode the coastline through abrasion and wave impact.

Sediment Transportation

Longshore drift allows sediment to move down the coast line. As material is eroded from headlands, it can then be redistributed down the shore.

Wave Depositional FeaturesWaves transport material forming barrier bars and sandspits

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Sandspit

Barrier bar

Excellent Erosional Resources

http://tvl1.geo.uc.edu/ice/Image/imageref.htmlhttp://nsidc.org/glaciers/index.htmlhttp://pubs.usgs.gov/gip/deserts/

The End