Weathering and Erosion Notes€¦ · Weathering Overview • Mechanical weathering breaks apart rocks so chemical weathering can change their composition. • Mechanical weathering

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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

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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