Transcript Weathering and Erosion

Constructive
and
Destructive
Forces
Weathering and Erosion
Weathering - processes at or
near Earth’s surface that cause
rocks and minerals to break
down
Erosion - process of removing
Earth materials from their
original sites through
weathering and transport
Weathering
Mechanical Weathering processes that break a rock or
mineral into smaller pieces
without altering its composition
Chemical Weathering processes that change the
chemical composition of rocks
and minerals
Agents of Mechanical
Weathering
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frost wedging
thermal expansion and contraction
mechanical exfoliation
abrasion by wind and water
plants and animals
Frost Wedging
Plant Wedging
Plant Roots
Friction and Repeated Impact
Burrowing of Animals
Chemical Weathering
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The process that breaks down rock through
chemical changes.
The agents of chemical weathering
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Water
Oxygen
Carbon dioxide
Living organisms
Acid rain
Water
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Water weathers rock by dissolving it
Oxygen
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Iron combines
with oxygen in
the presence of
water in a
process called
oxidation
The product of
oxidation is
rust.
Living Organisms
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Lichens that grow on rocks produce weak
acids that chemically weather rock
Acid Rain
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Compounds from burning coal, oil
and gas react chemically with water
forming acids.
Acid rain causes very rapid chemical
weathering.
Karst Topography
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A type of landscape in rainy regions
where there is limestone near the
surface, characterized by caves,
sinkholes, and disappearing
streams.
Created by chemical weathering of
limestone.
Features of Karst: Sinkholes
Features of Karst: Caves
Erosion
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The process by which water, ice, wind or
gravity moves fragments of rock and soil.
Water Erosion
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Rivers, streams, and runoff
Ice Erosion
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Glaciers
Wind Erosion
Mass Movements
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Landslides, mudslides, slump and creep
landslide clip.mpeg
Streams
Stream Erosion and Deposition
Glaciers
Wind Transport of Dust
Wind Transport of Dust
Deposition Formation
Volcanoes
Earthquakes
Mountain Building
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Weathering Controls
The type, rate and extent of weathering
depends upon several controlling factors:
Climate dictates the type of weathering
processes that operate, largely by
determining the amount of water available
and the temperature at which the processes
occur. Chemical reactions are faster at
higher temperatures, while frost wedging
occurs in colder climates.
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Rock Type determines the resistance of the
rock to the weathering processes that
operate in that particular environment. Each
rock type is composed of a particular set of
minerals, which are joined together by
crystallization, chemical bonding or
cementing. When the forces of plate
tectonics move these rocks from the
environment in which they formed and
expose them to the atmosphere they begin
to weather.
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Rock Structure: highly jointed or faulted
rocks present many planes of weakness
along which weathering agents (e.g. water)
can penetrate into the rock mass (Figures 1
& 2).
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Time: the duration of the period that the
same type of weathering has been operating,
uninterrupted by climatic change, earth
movements, and other factors, determines
the degree and depth to which the rocks
have been weathered.
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Topography: the slope angle determines
the energy of the weathering system by
controlling the rate at which water passes
through the rock mass. Generally, higher, or
tectonically active areas with steeper slopes
have more dynamic weathering systems,
whereas flat plains have slower weathering
systems.
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Erosion Processes
Erosion processes are usually considered
under four distinct categories:
Mass Wasting: the processes that occur on
slopes, under the influence of gravity, in
which water may play a part, although
water is not the main transporting medium.
Mass wasting, or landsliding
Rapid or Slow Changes
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Glaciers melt and form rivers.
Wind weathers rocks into sand.
Earthquakes move land and rocks.
Rivers carry sediment and build deltas.
How does a river become more
shallow over time?
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Small amounts of soil is deposited
each time the river current slowed
down causing the river to become
more shallow.