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Topic IV: Weathering

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How is the Earth s surface shaped by weathering, erosion, and deposition ? ... be broken down by weathering so that it can be transported by the agents of erosion. – PowerPoint PPT presentation

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Title: Topic IV: Weathering


1
Topic IV Weathering Erosion
  • The Destructive Geologic Forces

2
When You Have Finished This Unit, You should be
able to answer the following questions...
  • How is the Earths crust affected by its
    environment ?
  • What are the products of weathering ?
  • How are the products of weathering transported ?
  • How are eroded materials deposited ?
  • How is the Earths surface shaped by weathering,
    erosion, and deposition ?

3
Definitions..
  • Weathering - the slow continuous process by which
    nature breaks down rock material into smaller
    particles. The two major types of weathering are
    mechanical chemical
  • Erosion - the breakdown and transport of
    weathered material by the agents of erosion -
    running water, wave and current action, glaciers,
    wind, and gravity.

4
Mechanical Weathering
  • The breakdown of rock material into smaller
    particles of the same material.
  • Example - Granite bedrock breaks down into
    smaller particles of granite

5
Agents of Mechanical (aka Physical) weathering
include...
  • Ice wedging
  • Frost action
  • Unloading
  • Plant Action
  • Animal Action

6
Ice Wedging
  • As water seeps into the pre-existing cracks in
    rocks, it may freeze.
  • As the water freezes, it expands.
  • The expanding freezing water wedges the crack in
    the rock further open.

7
Frost Action
  • As rock material is heated, it expands.
  • The exterior of the rock may be heated while the
    interior is still cold and contracted from the
    cold night temps.
  • This pulls the outer layer of rock away in a
    process called exfoliation.

8
Unloading
  • When rock which has been buried by other
    sediment, rock, or ice is exposed, it may expand
    under the released pressure.
  • This expansion causes the outer layers of rock to
    exfoliate

9
Animal Action
  • As animals burrow into rock and soil, they break
    the material down into smaller particles of the
    same material.
  • Examples include worms, ground hogs, chipmunks,
    etc.

10
Plant Action
  • The roots of growing plants will grow into
    existing cracks of rock and enlarge the openings.
  • Smaller plants (lichens, e.g.) dig their tiny
    roots into small cracks with the same result.

11
Chemical Weathering...
  • involves the breakdown of rock material into new
    material with a new chemical make-up. In other
    words, the rock has turned into new rock
    material. (decomposition)
  • Agents of chemical weathering include oxidation,
    carbonation, hydration, and dissolution.

12
Oxidation
  • Oxidation is the chemical union of oxygen with a
    molecule within the rock. Rust is a common
    form of oxidation and is seen on many iron rich
    rocks around the ONeill campus.

13
Carbonation
  • As water falls through the atmosphere, a mild
    acid forms which can dissolve away limestone to
    form caves.

14
Hydration
  • The chemical union of water molecules with
    mineral molecules is known as hydration.
  • Iron and magnesium minerals will alter to clay
    minerals due to hydration. Feldspar also
    hydrates to form clay minerals.

15
Dissolution...
  • Certain minerals will actually dissolve when
    exposed to water or mild acids. The sample shown
    here is halite, a highly soluble mineral more
    commonly known as rock salt

16
In order for erosion to occur...
  • Material must first be broken down by weathering
    so that it can be transported by the agents of
    erosion.
  • Remember that chemical weathering can only occur
    on exposed surfaces.
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