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Weathering and Erosion
What is weathering?
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Weathering is process of breaking down and changing of rock
at or near Earth’s surface.
The two types of weathering are mechanical and chemical
weathering.
What is mechanical weathering?
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Mechanical weathering is the process of physical forces
breaking down rocks into smaller and smaller pieces without
changing the type of rock.
The causes of mechanical weathering are Frost wedging,
Unloading, and Biological activity.
What is frost wedging?
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Frost wedging is a rock break-up caused by the expansion of
freezing water in cracks and crevices.
The broken down pieces are known as talus.
What is unloading?
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Unloading is when large masses of igneous rock are exposed
through uplift, and erosion of over lying rocks.
This reduces the pressure on the rock causing the rock layers
to break away which is known as exfoliation.
What is biological activity?
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Biological activity are the activities of living organisms that
cause the breaking up of rock.
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Roots of trees break rock apart
Burrowing Animals move rocks to the surface where weathering is
more rapid.
Decaying Organisms- produce acid compounds that cause
chemical weathering.
Humans- accelerate mechanical weathering through deforestation
and blasting in search of minerals or in the creation of new roads.
What is chemical weathering?
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Chemical weathering is the process when rock turns
into one or more new compounds.
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Analogy:
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mechanical – tearing paper
chemical – burning paper
Water is the most important agent of chemical
weathering.
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water absorbs gases from the atmosphere and ground.
these dissolved substances chemically react with various
minerals.
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Rust - is iron oxide that forms when iron containing objects are exposed to
water.
Acid rain – is forms when rain absorbs carbon dioxide as it falls. This acid
breaks down rocks.
What are 3 factors that affect the rate
of weathering?
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Mechanical weather
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Breaks rock into smaller pieces, which increasing the surface area
of exposed rocks & accelerates chemical weathering
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Rock Characteristics
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Physical characteristics such as cracks can effect the ability for a
rock to be penetrated.
Mineral composition increase or decrease rate of weathering.
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Climate
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controls the frequency of freeze-thaw cycles and affects the rate of
mechanical weathering.
What is Erosion?
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Erosion is when Earth’s surface is transported by factors such
as, mass movement, water, glaciers, & wind.
These factors move soil from one place to another.
The single most important erosional
agent on Earth is moving water.
Mass Movements
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The transfer of rock and soil down slope due to
gravity is called mass movement.
Among the factors that commonly trigger mass
movements are
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Water: saturation of surface materials with water decreases
friction.
Slopes: Steepening of slopes unstabilizes angles
Removal of vegetation: Loosens soil
Earthquakes & Volcanic eruptions: Destabilizes rock
Types of Mass Movements
Geologists classify mass movements based
on the kind of material that moves, how it
moves, and the speed of movement.
Rockfalls
Slides
Slumps
Flows
Nat Geo
videoclip
Water Erosion
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The four types of water erosion are as
follows:
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the movement of soil by rain splash and its
transport by this surface flow.
Rill erosion by concentrated flow in small rivulets.
Gully erosion by runoff scouring large channels
(deeper than 1 foot).
Streambank erosion by rivers or streams cutting
into banks.
Stream Erosion
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Streams generally erode their channels,
lifting loose particles by abrasion, grinding,
and by dissolving soluble material.
A stream’s bedload is solid material too
large to carry in suspension.
Deposition occurs as stream flow slows down
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Larger, heavier particles are deposited first
Glacier Erosion
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Glaciers mainly erode in two ways:
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Plucking is when the bottom layer of a glacier melts and
the water seeps into the surrounding rock. This water then
refreezes and cracks and splits the rock. These rocks are
then incorporated into the glacier.
Abrasion occurs when a glacier made of ice and rock
moves over a bedrock surface which is then scraped and
smoothed by the glacier.
Glacial drift applies to all sediments deposited by
glaciers.
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There are two types of glacial drift: till and stratified drift.
Glacier Erosion
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Glacial drift applies to all sediments
deposited by glaciers.
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Till is deposited as the glacier melts and drops its
load of rock debris. Ice cannot sort the sediment
it carries, therefore till deposits are usually
unsorted mixtures made up of many particle
sizes.
Stratified drift is sediment laid down by glacial
meltwater. It contains particles that are sorted
according to size and weight of the debris.
Wind Erosion
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In general, most erosion results from running
water, although in deserts, wind erosion is
more significant than elsewhere because
deserts soils are dry.
Wind erodes in the desert in two ways:
deflation and abrasion.
Deflation
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Deflation is the lifting and removal of loose particles
such as clay and silt.
Deflation can lower elevation of land by a meter or
more.
Deflation also results in shallow depressions called
blowouts.
Deflation creates a stony surface layer called desert
pavement when it removes all the sand and silt and
leaves only coarser particles.
Abrasion
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Abrasion happens when wind-blown sand
cuts and polishes exposed rock surfaces.
Blowing sand can grind away at boulders
and smaller rocks, sometimes sandblasting
them into odd shapes.
How do humans affect erosion?
Erosion is strongly influenced by human activity:
 Removal of natural vegetation, such as farming,
logging, & construction greatly increase erosion.
 Over-steepened slopes due to construction can lead
to instability of soil and mass movements.
Essay- 1 full page and hand in
w/your name on it
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Write an essay about how humans
impact their the Earth’s landscape.
In your essay, include how humans
affect erosion.
Are humans’ effects on Earth’s
landscape a good or bad thing?
Why?