Download Weathering and Erosion Notes

9/30/2014
Mechanical Weathering
Earth’s surface processes
Weathering – Physical breakdown and
chemical alteration of rock at Earth’s
surface
• Mechanical weathering – breaking of rocks
into smaller pieces
1)
2)
3)
2 kinds of Weathering –
mechanical and chemical
4)
5)
6)
7)
Frost Wedging
Abrasion
Plant/Animal Activity
Gravity/Pressure
Wetting/Drying
Exfoliation / Joint Sheeting
Thermal Stress
Rockfall caused by frost wedging
Frost wedging – freezing and thawing of
water in cracks disintegrates rocks
Abrasion
Scraping of the surface by moving particles
during their transport by wind, glacier,
waves, gravity, running water or erosion.
Glacial Abrasion
Geology.com
Plant/Animal Activity
• The activity of organisms,
including plants, burrowing
animals, and humans, can also
cause mechanical weathering.
Sandblasting abrasion
National Geographic.com
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Gravity/Pressure
• Bedrock is under pressure from overlying
rock. When overlying rock layers are
removed, the pressure on bedrock is
reduced and it expands and cracks.
www.geologycafe.com
Mechanical Exfoliation / Joint Sheeting
Reduced pressure caused by “unloading” on igneous
rock causes it to expand and allows slabs of outer rock
to break off in layers in a process called exfoliation.
Chemical Weathering
• Breaks down rock and minerals by
changing their composition.
• 5 Types of Chemical Weathering:
1.
2.
3.
4.
5.
Wetting/Drying
• Wetting and drying causes clay minerals
to expand and contract, and salts may
dissolve and re-precipitate.
Shale (mostly clay)
weathering from
Wetting/Drying cycles
www.sandatlas.org
Picture to demonstrate
shrink/swell potential of clay
www.agronomy.lsu.udu
Thermal Stress
Heating up and cooling down makes
rocks swell and shrink until they break.
Dissolution of Soluble Compounds
• CO2 mixed with water forms
carbonic acid.
• Dissolves soluble compounds
(calcium, limestone) in rocks
• Forms caves
Dissolution (Carbon Dioxide)
Hydrolysis
Oxidation
Acid Precipitation
Organic (Plant) Acids
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Hydrolysis
• Water reacts with silicate and carbonate
minerals. Pure water ionizes and reacts
with silicate minerals and decomposes
rocks.
Oxidation
• Chemical reaction where oxygen combines
with minerals in rocks.
• Example: Oxygen combines with Iron (Fe)
and forms rust (iron oxide).
http://claremontgeography12.blogspot.com/2011/02/hydrolysis.html
Acid Precipitation
•Sulfur dioxide
(SOx) forms from the
burning of fossil fuels
(factories & trucks) and
turns into sulfuric acid.
Organic (Plant) Acids
• Plants and fungi release chemicals that
break down rocks and release minerals.
Lichen (Algae and Fungus)
2 Reasons For This:
• Dissolving Nutrients
• Making Surface for Growth
•It rains down as acid
rain, breaking down
rock and buildings.
http://mrsmaineswiki.wikispaces.com/file/view/acid-rain-1a.jpg/31982777/acid-rain-1a.jpg
http://envis.tropmet.res.in/kidscorner/KidsCornerImg/acid_rain/acidr5.jpg
Types of Mechanical Weathering
Warm Up 3/14/14
• Explain the difference between chemical
and physical weathering.
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Climate Affects Weathering Rates!
Cleopatra’s Needle
was in Egypt for
3500 years. In 1880
it was moved to
NYC. In 75 years it
weathered so that
most of the writing
is gone.
Climate Affects Weathering Rates
• Tropics – Hotter, more rain fall = more chemical
weathering.
• Cool, Dry Climates – Much more mechanical
weathering due to freeze / thaw cycles.
More water = more
weathering
Granite in a
Dry Climate
Granite in a
Wet Climate
http://www.briangwilliams.us/geology/startup-activities-1.html
Topography Affects Weathering Rates!
Rock Composition Affects
Weathering Rates!
2
• Which rock
will weather
the fastest?
• Which rock
will weather
the slowest?
1
http://www.earthhistory.org.uk/creation-theory/introduction
• Which area will weather the fastest? Why?
http://edtech2.boisestate.edu/gaffordm/502/conceptmap.html
Weathering Overview
• Mechanical weathering breaks apart
rocks so chemical weathering can change
their composition.
• Mechanical weathering increases surface
area available for chemical weathering.
Erosion and Deposition
• Erosion- the process that transports Earth
materials from one place to another; can
be on a small scale or can be a massmovement.
• Deposition – the process that drops
materials in another location.
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Forces of Erosion
Gravity
• Gravity pulls materials downslope
• Running water moves across Earth from higher to
lower elevations (gravity)
• Extreme examples: landslides, avalanches, &
mudflows.
http://kids.britannica.com/elementary/art-88797/Water-wind-glaciers-and-gravity-all-can-change-the-land
http://www.sfu.ca/geog/geog351fall06/group06/Landslides/pic_of_mudflow.jpg
Slope Stabilization Efforts
Slope Stabilization Efforts
Vegetation and
rocks can also
prevent erosion
Mountain
Farmers use
terracing
(stair-steps)
to avoid
erosion
http://vetivernetinternational.blogspot.com/2012/12/stabilizing-and-regreening-gunnited.html
http://www.planetware.com/i/photo/gunung-kawi-tampaksiring-ina221.jpg
http://www.dec.ny.gov/permits/67096.html
Slope Stabilization Efforts
Water
• Rain
• Streams and
rivers
• Ocean waves
and tides
• Ice (glaciers)
http://www.geobrugg.com/contento/en-us/Home/Slopestabilization/tabid/2061/Default.aspx
TECCO® high-tensile mesh slope stabilization system
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Streams & Rivers
Streams
Rivers
Streams and Rivers: Deposition
Ocean
• Flowing water has great power; can carry material
long distances.
• The Mississippi River (“The Big Muddy”) carries 750
million metric tons of eroded material into the Gulf of
Mexico each year!
Ocean Waves and Tides
Erosioncontrolpro.com
•Deposition: Sediments that erode inland
and travel down rivers build up in deltas.
Protecting Beaches
• Sand at the beach = weathered deposits
• Coasts – wind and waves erode and deposit sand;
constantly shifting.
Groins
Cape Hatteras Lighthouse
•1870 – built 500 m from the sea
•1987 – only 50 m from the sea
•1999 – moved ½ mile inland to protect it
Beach Erosion
http://www.lindsayfincher.c om/gallery/d/16199-2/cape_hatteras_lighthouse_beach_22.JPG
http://faculty.gvs u.edu/videtic p/beach_drift.GIF
http://www.maine.gov/doc/nrimc/mgs/explore/marine/faq/groins.gif
http://kanat.jsc.vsc.edu/student/davis/images/groins.jpg
Jetties
Seawalls
http://texascoastgeology.com/passes/Packery%20jetties%207-22-05.jpg
North Myrtle Beach, South Carolina
http://portaransasbuyersbroker.com/realestate/aerial1.jpg
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Beach Nourishment
Replanting
Dune
Vegetation &
Controlling
Development
From the town of Ocean
City Website: "Ocean
City’s Beach
Replenishment Project is
an on going effort. Twice
a year the Army Corps of
Engineers survey our
beach to determine the
need for any additional
sand. In general, the
dredging is on a four year
cycle. The last project
was completed in 2002.
This year (2006) we will
be pumping
approximately 830,000
cubic yards of sand."
http://www.octhebeach.com/images-things/beach-replenishment-b.jpg
Ocean City, Maryland
http://www.dkimages.com/discover/previews/754/414234.JPG
Glaciers
Glaciers
• Deposit material
in piles called
moraines.
• Fields of ice that scrape against the bedrock, carrying huge
rocks and piles of debris over great distances.
• When they melt
and recede, they
release all of the
dirt and gravel
they picked up
called glacial
outwash.
http://faculty.ccc.edu/jtassin/geology201/labs/glaciation/glaciation.htm
Wind
The Dust Bowl of the Great Plains
During the 1930s, a combination of drought & poor soil
conservation led to severe
wind erosion of topsoil in
what is known as the Dust
Bowl of the Great Plains.
http://www.usd.edu/anth/epa/dust.html
http://ees.kuleuven.be/geography/projects/151/6611_f5.jpg
Especially important in areas with less vegetation to cover and
hold soil in place.
Wind picks up and moves fine, dry soil particles and deposits
them elsewhere...BIG problem for farmers!
http://www.usd.edu/anth/epa/dust.html
Dust Bowl
http://1.bp.blogspot.com/_pZO0lOEj1oo/SpwsFD4q7TI/AAAAAAAACcY/HgZu7-gOfZc/s400/831+dust+bowl+car.jpg
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Preventing Soil Erosion
•
Contour farming
follows natural
land contours
•
Strip cropping
maintains strips of
different vegetation
between crops
Preventing Soil Erosion
Conservation–tillage farming minimizes soil disturbance
by use of special tillers or by no–till methods that inject
seeds, fertilizers, & herbicides in unplowed soil
“Pretty, green cotton
• Windbreaks made
from trees or other
barriers reduce
loss of soil by wind
http://www.johnehrenfeld.com/book/images/Contour%20plowing.jpg
plants emerge from a
field that was
previously planted to
wheat. The stalks
left from the wheat
harvest provide the
soil in the field with
protection against
erosion caused by
high winds. The old
wheat (crop)
residues also keep
more water on the
fields and serve as a
natural filter during
heavy rains.”
http://www2.ctic.purdue.edu/Core4/CT/PhotosGraphics.html
http://www2.ctic.purdue.edu/Core4/CT/PhotosGraphics.htm l
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