Weathering

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Weathering
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What is weathering?

• Weathering is a set of physical and chemical
  processes that change the physical and chemical
  properties of rocks and soil at or near the
  earth's surface.

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More about weathering

• Definition the breakdown of rock to form
  sediment very small pieces of rock
• Weathering happens to rocks that are NOT MOVING
• Weathering is part of the Rock Cycle

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There are two types of weathering

• Mechanical also called physical
• Chemical

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• Mechanical weathering breaks rocks down into
  smaller pieces, but does not change the
  composition of the rock.

Types of mechanical weathering include
Frost wedging Exfoliation Thermal
expansion Root pry Animal
activity Abrasion
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• Chemical weathering breaks rocks down chemically
  adding or removing chemical elements, and changes
  them into other materials.
• Chemical weathering consists of chemical
  reactions, most of which involve water.

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• The mechanical breakdown of rock caused by the
  action of living organisms, including plants and
  burrowing animals

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Lets investigate mechanical weathering first.
Click to see a video clip about mechanical
weathering
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In mechanical weathering, a rock is broken down
into smaller pieces without changing its mineral
composition.
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Enchanted rock is a huge example of exfoliation
mechanical weathering close to home.
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Review mechanical weathering

• breaks rocks down into smaller pieces.
• Types of mechanical weathering include
• frost wedging ice in cracks expands
• exfoliation - rock breaks off into sheets
• thermal expansion and contraction heating and
  cooling
• abrasion - wind, waves, rain, glaciers, and so on
  rub (abrade) rocks' surfaces, wearing them down
• Root Pry and Animal Actions living things
  physically changing rock

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Now, lets look at chemical weathering.
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In chemical weathering, a rock is broken down by
chemical reactions that change its mineral
composition and physical and chemical
properties.Water is most often a part of
chemical weathering.
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• Chemical weathering happens when the minerals
  that make up a rock are changed, leading to the
  disintegration of the rock.

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Physical and chemical weathering occur together.
Physical weathering breaks rocks into pieces so
more surface is exposed to chemical weathering
which breaks it down further.Click on the
picture to watch the video.
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• Chemical weathering happens quickly in warm,
  moist environments because water is needed for
  the chemical reactions.
• The warm weather speeds up the reactions.

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• Not all minerals are prone to chemical
  weathering.
• For example feldspar and quartz, common minerals
  in the rock granite, have very different levels
  of resistance to chemical weathering.
• Quartz doesnt weather very easily, but feldspar
  does. Over a long time, it chemically changes
  into clay minerals.

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Lichens on rocks cause chemical weathering.
A lichen is a combination of fungus and algae,
living together in a symbiotic relationship.
Lichens can live on bare rock, and they break
down rocks by secreting acids and other chemicals.
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Review weatheringscroll down the page to
review all three types of weathering