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Weathering and Erosion Notes 9/30/2014 Mechanical Weathering Earth’s surface processes • Mechanical weathering – breaking of rocks into smaller pieces Weathering – Physical breakdown and chemical alteration of rock at Earth’s 1) Frost Wedging surface 2) Abrasion 3) Plant/Animal Activity 2 kinds of Weathering – 4) Gravity/Pressure mechanical and chemical 5) Wetting/Drying 6) Exfoliation / Joint Sheeting 7) Thermal Stress Rockfall caused by frost wedging Frost wedging – freezing and thawing of water in cracks disintegrates rocks Abrasion Plant/Animal Activity Scraping of the surface by moving particles during their transport by wind, glacier, • The activity of organisms, waves, gravity, running water or erosion. including plants, burrowing Glacial Abrasion Geology.com animals, and humans, can also cause mechanical weathering. Sandblasting abrasion National Geographic.com 1 9/30/2014 Gravity/Pressure Wetting/Drying • Bedrock is under pressure from overlying • Wetting and drying causes clay minerals rock. When overlying rock layers are to expand and contract, and salts may removed, the pressure on bedrock is dissolve and re-precipitate. reduced and it expands and cracks. Picture to demonstrate Shale (mostly clay) shrink/swell potential of clay weathering from www.agronomy.lsu.udu Wetting/Drying cycles www.sandatlas.org www.geologycafe.com Mechanical Exfoliation / Joint Sheeting Reduced pressure caused by “unloading” on igneous Thermal Stress rock causes it to expand and allows slabs of outer rock Heating up and cooling down makes to break off in layers in a process called exfoliation. rocks swell and shrink until they break. Chemical Weathering Dissolution of Soluble Compounds • CO 2 mixed with water forms • Breaks down rock and minerals by carbonic acid. changing their composition. • Dissolves soluble compounds (calcium, limestone) in rocks • 5 Types of Chemical Weathering: • Forms caves 1. Dissolution (Carbon Dioxide) 2. Hydrolysis 3. Oxidation 4. Acid Precipitation 5. Organic (Plant) Acids 2 9/30/2014 Hydrolysis Oxidation • Chemical reaction where oxygen combines • Water reacts with silicate and carbonate with minerals in rocks. minerals. Pure water ionizes and reacts • Example: Oxygen combines with Iron (Fe) with silicate minerals and decomposes and forms rust (iron oxide). rocks. http://claremontgeography12.blogspot.com/2011/02/hydrolysis.html Acid Precipitation Organic (Plant) Acids •Sulfur dioxide • Plants and fungi release chemicals that (SOx) forms from the break down rocks and release minerals. burning of fossil fuels Lichen (Algae and Fungus) (factories & trucks) and 2 Reasons For This: turns into sulfuric acid. • 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. 3 9/30/2014 Climate Affects Weathering Rates! Climate Affects Weathering Rates Cleopatra’s Needle was in Egypt for • Tropics – Hotter, more rain fall = more chemical 3500 years. In 1880 weathering. it was moved to • Cool, Dry Climates – Much more mechanical NYC. In 75 years it weathering due to freeze / thaw cycles. weathered so that most of the writing is gone. More water = more weathering Granite in a Granite in a Dry Climate 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 1 will weather http://www.earthhistory.org.uk/creation-theory/introduction the slowest? • Which area will weather the fastest? Why? http://edtech2.boisestate.edu/gaffordm/502/conceptmap.html Weathering Overview • Mechanical weathering breaks apart Erosion and Deposition rocks so chemical weathering can change their composition. • Erosion- the process that transports Earth materials from one place to another; can be on a small scale or can be a mass- • Mechanical weathering increases surface movement. area available for chemical weathering. • Deposition – the process that drops materials in another location. 4 9/30/2014 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 Mountain rocks can also Farmers use prevent erosion 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 5 9/30/2014 Streams & Rivers Streams and Rivers: Deposition Streams Rivers Ocean • Flowing water has great power; can carry material Erosioncontrolpro.com long distances. •Deposition: Sediments that erode inland • The Mississippi River (“The Big Muddy”) carries 750 and travel down rivers build up in deltas . million metric tons of eroded material into the Gulf of Mexico each year! Ocean Waves and Tides Protecting Beaches • Sand at the beach = weathered deposits • Coasts – wind and waves erode and deposit sand; Groins constantly shifting. 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.com/gallery/d/16199-2/cape_hatteras_lighthouse_beach_22.JPG http://faculty.gvsu.edu/videticp/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 6 9/30/2014 Beach Nourishment Replanting From the town of Ocean City Website: "Ocean City’s Beach Dune Replenishment Project is an on going effort. Twice a year the Army Corps of Vegetation & Engineers survey our beach to determine the need for any additional Controlling sand. In general, the dredging is on a four year cycle. The last project Development 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. • When they melt and recede, they release all of the dirt and gravel they picked up called glacial • Fields of ice that scrape against the bedrock, carrying huge outwash. rocks and piles of debris over great distances. http://faculty.ccc.edu/jtassin/geology201/labs/glaciation/glaciation.htm Wind The Dust Bowl of the Great Plains 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. 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 http://www.usd.edu/anth/epa/dust.html them elsewhere...BIG problem for farmers! Dust Bowl http://1.bp.blogspot.com/_pZO0lOEj1oo/SpwsFD4q7TI/AAAAAAAACcY/HgZu7-gOfZc/s400/831+dust+bowl+car.jpg 7 9/30/2014 Preventing Soil Erosion Preventing Soil Erosion Conservation–tillage farming minimizes soil disturbance • Contour farming by use of special tillers or by no–till methods that inject follows natural seeds, fertilizers, & herbicides in unplowed soil land contours “Pretty, green cotton plants emerge from a • Strip cropping field that was maintains strips of previously planted to wheat . The stalks different vegetation left from the wheat harvest provide the between crops soil in the field with protection against erosion caused by • Windbreaks made high winds. The old wheat (crop) from trees or other residues also keep barriers reduce more water on the fields and serve as a loss of soil by wind http://www.johnehrenfeld.com/book/images/Contour%20plowing.jpg natural filter during heavy rains.” http://www2.ctic.purdue.edu/Core4/CT/PhotosGraphics.html http://www2.ctic.purdue.edu/Core4/CT/PhotosGraphics.html 8.
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