Erosion and

DepositionAgents, Forces, and Results

Presented byMd. Nazir Hossain

LecturerGeography and Environment

Shahjalal University of Science & TechnologySylhet-3114, Bangladeshnazirswapon@gmail.com

GEE-421: Geomorphology-IIChapter 1

What Caused This?

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What is Erosion?•Erosion – moving of rock material from one place to a new location– Three processes must take place:

• detachment of particles • lifting them• transporting them

– Agents of erosion:• flowing water• moving ice• waves• gravity• wind

•Water – most influential force in erosion– Moves materials – Transports large objects with fast moving streams– Wears away rocks:

• rivers• lakes• oceans

What Is Water Erosion?

Erosion caused by flooding

•Wind – responsible for wearing away rocks and creating great deserts like the Sahara Desert and Gobi– Most effective in moving loose material – Main effects:

1. Wind causes small particles to be lifted and moved away. 2. Suspended particles may impact on solid objects causing erosion by

abrasion (rubbing).– Occurs in areas where there is not enough rainfall to support vegetation

What Is Wind Erosion?

Extreme erosion caused by wind over long periods of time

•Waves – relentless pounding • Erodes:

• softer/weaker rock first• harder/more resistant left behind

• Can take over 100 years to erode a rock to sand • Energy of waves and chemical content of the water erodes

the rock of the coastline.

What is Wave Erosion?

• Ice – moves and carries rocks, grinding the rocks beneath the glacier–Plucking occurs when water enters cracks under the glacier.

• freezing• breaking off pieces of rock that are then carried by the

glacier–Abrade (abrasion)

• cuts into the rock under the glacier• smoothing • polishing the rock surface

What Is Glacial Erosion?

•Mass movement – downward movement of rock and sediments, mainly due to the force of gravity –Streams and glaciers

• move material from higher to lower elevation– Occurs continuously on all slopes

» slow moving and sudden movement until equilibrium is reached

What is Gravitational Erosion?

What is Deposition?

Deposition – laying down of sediment that has been transported by a medium such as wind, water, or ice – Process of erosion stops:

• when the moving particles fall out of the transporting medium and settle on a surface

– Speed of the medium slows or the resistance of the particles increases, the balance changes and causes deposition

– Speed can be reduced by large rocks, hills, vegetation, etc.

• Running water enters a large, fairly still body of water and its speed decreases. • SPEED

• As the speed of the water decreases, the water's ability to carry sediment also decreases.

• Deposited in streams, rivers, and oceans:• Running water deposits sediments where the slowing water can no

longer move them.• Largest particles are deposited near the shore. • Increasingly smaller particles settle out farther from the shore where

the water is calmer.

Deposition - Water

Wind speed can be related to variations in heating and cooling.Transportation of particles in wind:

– Fine particles in suspension hundreds of km from its original source in the desert

– Heavier material may be blown along the ground.– Material is deposited when the wind changes direction or loses its

strength.

Deposition - Wind

• Glacial flows of ice – become slower when the ice begins melting

– Deposits left by glaciers:– The deposits of these rivers look similar to normal river deposits and are

called outwashes.– Moraines are large mass of broken rock left at the base and sides of the

glacier.– Finer material is carried in the rivers that form when the glacial ice melts.

Deposition - Ice

• WEATHERING – Think of weather wearing rock down.

• EROSION – Think of a road and traveling.

• DEPOSITION – Think of depositing money into a bank.

What’s the Difference?

Next Topic

Weathering

Thanks To All