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9/30/2014
1
Earth’s surface processes
Weathering – Physical breakdown and chemical alteration of rock at Earth’s surface
2 kinds of Weathering –
mechanical and chemical
Mechanical Weathering• Mechanical weathering – breaking of rocks
into smaller pieces
1) Frost Wedging2) Abrasion
3) Plant/Animal Activity4) Gravity/Pressure
5) Wetting/Drying 6) Exfoliation / Joint Sheeting7) Thermal Stress
Frost wedging – freezing and thawing of water in cracks disintegrates rocks
Rockfall caused by frost wedging
AbrasionScraping of the surface by moving particles during their transport by wind, glacier, waves, gravity, running water or erosion.
Glacial Abrasion Geology.com
Sandblasting abrasion
• The activity of organisms, including plants, burrowing animals, and humans, can also cause mechanical weathering.
Plant/Animal Activity
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
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 cycleswww.sandatlas.org
Picture to demonstrate shrink/swell potential of clay
www.agronomy.lsu.udu
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.
Thermal Stress
Heating up and cooling down makes rocks swell and shrink until they break.
Chemical Weathering
• Breaks down rock and minerals by changing their composition.
• 5 Types of Chemical Weathering:1. Dissolution (Carbon Dioxide)2. Hydrolysis3. Oxidation
4. Acid Precipitation5. Organic (Plant) Acids
Dissolution of Soluble Compounds• CO2 mixed with water forms carbonic acid.
• Dissolves soluble compounds (calcium, limestone) in rocks
• Forms caves
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Hydrolysis• Water reacts with silicate and carbonate
minerals. Pure water ionizes and reacts with silicate minerals and decomposes rocks.
http://claremontgeography12.blogspot.com/2011/02/hydrolysis.html
Oxidation• Chemical reaction where oxygen combines
with minerals in rocks.• Example: Oxygen combines with Iron (Fe)
and forms rust (iron oxide).
Acid Precipitation
•Sulfur dioxide (SOx) forms from the burning of fossil fuels (factories & trucks) and turns into sulfuric acid.
•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
Organic (Plant) Acids
• Plants and fungi release chemicals that break down rocks and release minerals.
2 Reasons For This:• Dissolving Nutrients• Making Surface for Growth
Lichen (Algae and Fungus)
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!
Granite in aDry Climate
Granite in aWet Climate
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.
More water = more weathering
Climate Affects Weathering Rates• Tropics – Hotter, more rain fall = more chemical
weathering.• Cool, Dry Climates – Much more mechanical
weathering due to freeze / thaw cycles.
http://www.briangwilliams.us/geology/startup-activities-1.html
Topography Affects Weathering Rates!
• Which area will weather the fastest? Why?
http://www.earthhistory.org.uk/creation-theory/introduction
1
2
Rock Composition Affects Weathering Rates!
• Which rock will weather the fastest?
• Which rock will weather the slowest?
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 mass-movement.
• Deposition – the process that drops materials in another location.
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Forces of Erosion
http://kids.britannica.com/elementary/art-88797/Water-wind-glaciers-and-gravity-all-can-change-the-land
Gravity• Gravity pulls materials downslope• Running water moves across Earth from higher to
lower elevations (gravity)• Extreme examples: landslides, avalanches, &
mudflows.
http://www.sfu.ca/geog/geog351fall06/group06/Landslides/pic_of_mudflow.jpg
Mountain Farmers use terracing(stair-steps) to avoid erosion
http://www.planetware.com/i/photo/gunung-kawi-tampaksiring-ina221.jpg
Slope Stabilization Efforts Slope Stabilization Efforts
http://vetivernetinternational.blogspot.com/2012/12/stabilizing-and-regreening-gunnited.html
http://www.dec.ny.gov/permits/67096.html
Vegetation and rocks can also prevent erosion
Slope Stabilization Efforts
http://www.geobrugg.com/contento/en-us/Home/Slopestabilization/tabid/2061/Default.aspx
TECCO® high-tensile mesh slope stabilization system
Water
• Rain• Streams and
rivers• Ocean waves
and tides• Ice (glaciers)
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Streams & Rivers
Streams Rivers 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!
Streams and Rivers: Deposition
•Deposition: Sediments that erode inland and travel down rivers build up in deltas .
Erosioncontrolpro.com
Ocean Waves and Tides
• Sand at the beach = weathered deposits
• Coasts – wind and waves erode and deposit sand; constantly shifting.
http://www.lindsayfincher.com/gallery/d/16199-2/cape_hatteras_lighthouse_beach_22.JPG
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
Protecting Beaches
Groins
http://www.maine.gov/doc/nrimc/mgs/explore/marine/faq/groins.gifhttp://faculty.gvsu.edu/videticp/beach_drift.GIF
http://kanat.jsc.vsc.edu/student/davis/images/groins.jpg
Jetties
http://texascoastgeology.com/passes/Packery%20jetties%207-22-05.jpg
http://portaransasbuyersbroker.com/realestate/aerial1.jpg
Seawalls
North Myrtle Beach, South Carolina
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Beach Nourishment
Ocean City, Maryland
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
Replanting Dune
Vegetation & Controlling
Development
http://www.dkimages.com/discover/previews/754/414234.JPG
Glaciers
• Fields of ice that scrape against the bedrock, carrying huge rocks and piles of debris over great distances.
Glaciers• Deposit material in piles called moraines.
• 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
� 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://ees.kuleuven.be/geography/projects/151/6611_f5.jpg
During the 1930s, a combi-nation of drought & poor soil conservation led to severe wind erosion of topsoil in
what is known as the Dust Bowl of the Great Plains.
The Dust Bowl of the Great Plains
http://www.usd.edu/anth/epa/dust.html
Dust Bowl
http://www.usd.edu/anth/epa/dust.html
http://1.bp.blogspot.com/_pZO0lOEj1oo/SpwsFD4q7TI/AAAAAAAACcY/HgZu7-gOfZc/s400/831+dust+bowl+car.jpg
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Preventing Soil Erosion
• Contour farmingfollows natural land contours
• Strip croppingmaintains strips of different vegetation between crops
• Windbreaks made from trees or other barriers reduce loss of soil by wind http://www.johnehrenfeld.com/book/images/Contour%20plowing.jpg
“Pretty, green cottonplants 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.”
Conservation–tillage farming minimizes soil disturbance by use of special tillers or by no–till methods that inject seeds, fertilizers, & herbicides in unplowed soil
Preventing Soil Erosion
http://www2.ctic.purdue.edu/Core4/CT/PhotosGraphics.html http://www2.ctic.purdue.edu/Core4/CT/PhotosGraphics.html