Changes in the Land The Effects of Weathering, Erosion and Deposition

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Changes in the LandThe Effects of Weathering,
Erosion and Deposition

• By Colby D.

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Weathering Mechanical Weathering

• Weathering occurs when the land is exposed to air
  and water, in the action of snow, frost, sun and
  rain, resulting in rock that has been broken down
  into smaller pieces to form sediment.
• Weathering takes place in several forms
  Mechanical Weathering, Chemical Weathering,
  Biological Weathering.

• Mechanical Weathering consists of Thermal
  Expansion and Freeze-thaw.
• Thermal Expansion will result from temperature
  changes, causing rocks to expand, contract and
  break apart.
• Freeze-thaw is caused by water inside rocks that
  freezes and expands, causing the rocks to form
  cracks and break apart .

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Weathering Chemical and Biological

• Chemical Weathering will take place when minerals
  are added or removed from rock.
• Rain water acts as a weak acid and can change or
  dissolve the chemicals in rock.
• Oxygen gas in the air will react with water and
  iron in the rock, resulting in oxidation and
  rust. This process causes rocks to soften and
  break apart.

• Biological Weathering is caused by tree and plant
  roots that act as wedges by breaking rock apart
  into smaller pieces of sediment or soil.
• Little animals also assist in the breaking down
  process by burrowing and digging through the
  ground.

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Biological Weathering
This picture shows how the roots of trees can
assist in the weathering process by acting like
wedges and breaking rock apart.
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Erosion Wind, Water and Ice

• The more rock area exposed to the elements, the
  faster the weathering, or break down of the rock.
• Erosion takes place in the removal of weathered
  rock or sediments by the forces of wind, water
  and ice.

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Erosion - Water

• Water is a primary eroder. Moving waters include
  strong rivers and little streams, the sea and
  also ice, which moves over the land as glaciers
  and ice-sheets.
• New and changing landforms are created by the
  action of rivers or glaciers wearing away rock.

• Running water in streams and rivers can carry
  materials that attack the bedrock of the river
  and create deeper V shaped valleys.
• Rivers flowing down steep slopes have strong
  cutting power.

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Erosion - Water
Erosion from a river can create Waterfalls,
Meanders, Flood Plains, Oxbow Lakes, Valleys, and
Canyons. This waterfall is located in
Yosemite National Park.
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Erosion

• As water or ice flows down from a mountain they
  carve out valleys, leaving ridges of rock and
  giving the mountains their shape.

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Erosion - Glaciers

• Today, glaciers cover only 10 of the Earths
  surface, but during the Ice Ages, when glaciers
  covered vast amounts of the Earths surface, a
  large amount of erosion occurred.
• The weight of glaciers and their continual
  movement of advancing, retreating, and melting
  back, cut away soils and boulders and push them
  along.

• Glaciers left behind various landforms, such as
• U Shaped Valleys,
• Kettle Lakes,
• Fiords, and
• Glacial Lakes
• The Great Lakes in Michigan and The Grand Teton
  Mountains in Wyoming, are examples of the
  enormous amount of erosion that glaciers can
  accomplish.

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Erosion - Glaciers
Pictured below are the glacially formed Wyoming,
Grand Teton Mountains.
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Erosion - Waves

• Waves are a strong erosionary force. Each time a
  wave breaks against a cliff, water is forced into
  the cracks. This weakens the rock, and over
  time, blocks and pieces of the cliff fall away.
• As the tide changes, the waves erode different
  parts of the beach. Sand is moved up a beach or
  dragged back down by the force of the waves.
• Beaches owe much of their shape and size to the
  pounding of the waves, and changes of the tide.

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Erosion-Wind

• Next to water, WIND is a primary eroder.
• Winds carry a variety of materials from silt to
  sand grains, which act as an abrasive, eroding
  exposed rock and soil.
• Winds can deposit sediments, as well as move
  them.
• Dunes are made by sand, carried and deposited by
  winds.
• The strong wind speeds in Tornadoes and
  Hurricanes can move material, such as boulders,
  rocks, sand and soils, accelerating erosion.

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Deposition

• Deposition takes place when the sediments that
  have been transported by water, ice and wind are
  deposited. These deposits contribute to the
  continual changing shape of the land.
• Gravel, rocks and boulders can be pushed along
  the bottom of a river, then be deposited at the
  mouth of the river, forming alluvial fans and
  deltas.

• Alluvial fans are formed when sediment from a
  stream, leaving a mountain range, form a wide,
  sloping deposit in the shape of a fan.
• A delta is a fan shaped landform, created by the
  build- up of sediment from a river as they flow
  into the ocean.

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Deposition
Large rivers like the Mississippi, send so much
eroded material to the sea, that the waves cannot
carry it away fast enough and large deltas are
formed. In the pictures below are satellite
images of the Mississippi River and Delta.
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Weathering, Erosion Deposition

• Weathering and erosion changes the land by
  wearing down mountains, filling in valleys, and
  making rivers appear and disappear.
• The pattern of erosion, making new rocks from
  old, is part of a cycle.
• Gradually great mountain ranges will be worn down
  to become hills and then plains.
• Small particles of rock carried by rivers and
  glaciers eventually end up in the sea, piling up
  sediments on the sea bed.
• After millions of years, they turn into
  sedimentary rocks like sandstone or clay.
  Gradually, those rocks could be pushed up to make
  new land and new mountain ranges. This new land
  will follow the cycle of erosion and will
  eventually be worn down by water, ice, and wind.