Transcript Topic IV: Weather & Erosion

Topic IV: Weathering &
Erosion
The “Destructive Geologic Forces”
When You Have Finished This
Unit, You should be able to
answer the following questions...
• How is the Earth’s 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 Earth’s surface shaped by
weathering, erosion, and deposition ?
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.
Mechanical Weathering
• The breakdown of rock material into
smaller particles of the same material.
• Example - Granite bedrock breaks down
into smaller particles of granite
Agents of Mechanical (aka
“Physical”) weathering include...
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Ice wedging
Frost action
Unloading
Plant Action
Animal Action
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.
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.
“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”
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.
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.
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.
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
O’Neill campus.
Carbonation
• As water falls
through the
atmosphere, a mild
acid forms which can
dissolve away
limestone to form
caves.
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.
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”
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.