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Unit 4: Weathering, Erosion, and Deposition (Text ch.5, 6, and 7) (Review Book p.130-168) I Weathering: the breakdown of rocks into sediments by exposure to air and water. (see text p.126) vidclip- Weathering intro. A. Physical (or Mechanical) Weathering: changes the shape or size of a rock. (How nature smashes rocks) 1. Frost Action (Wedging): During the day, liquid water seeps into cracks in the rock. At night, water freezes and expands, breaking rock apart. (see text p.127) [Diagram] frost wedging animation Observe the effects of mechanical weathering. 2. Plant Roots grow into cracks, breaking rock apart. (see text p.128) plant action animation Observe the effects of mechanical weathering. 3. Abrasion: sediments are transported by water,or wind. They wear away by bumping and grinding together. [diagram] stream abraded rocks YouTube - Bill Nye the Science Guy - Pet Rock Theatre 4. Exfoliation: occurs when heavy pressure is removed from underlying rocks. (see text p.128) exfoliation animation exfoliation weathering - Google Images 5. Physical Weathering increases the surface area and allows chemicals to break rock apart faster. (see text p.127) [diagram] vidclip- mechanical or physical weathering B. Chemical Weathering: changes the chemical composition of the rock. 1. Water (H2O) is the most important agent of chemical weathering H2O combines with minerals and weakens them. Ex. Feldspar + Water → Clay + Salt (makes oceans salty) H2O speeds up the rate of all other chemical reactions. H2O absorbs gases such as oxygen (O2) or carbon dioxide (CO2) that weaken or dissolve rock. 2. Oxygen combines with iron rich minerals to form iron oxide or rust. Iron + O2 → Iron Oxide (rust) rock oxidation - Google Images 3. Carbon Dioxide dissolves in water to form Carbonic Acid. [Demo- form carbonic acid] This dissolves rocks, especially limestone, forming caverns and sinkholes (text p. 177, 179). image karst topography Observe an animation of cave formation. Example: Howe Caverns in N.Y. Howe Caverns: Year Round Adventure ES 2008-09\Unit 4 08-09\Cave_Formation.asf YouTube - Planet Earth - Caves 1/5 Chemical_Weathering.asf C. Factors affecting how fast rocks weather. 1. Mineral Composition ex.: see text p.129 fig. 6 gravestone weathering - Google Image Search More resistant rocks stick out as less resistant rocks weather away. [Diagram] buttes - Google Image Search rock strata- grand canyon 2. Climate Rocks weather fastest in warm, moist climates. Rocks weather slowest in dry climates. mayan pyramid egyptian pyramids 3. Air Pollution, especially Acid Rain, weathers rocks faster. See text p.130 Cleopatra's Needle in Central Park- NYC “Cleopatra's Needle, an Egyptian obelisk, has been used for illustration of weathering processes in numerous geology textbooks (Figure 15). The obelisk was donated to the United States and erected at its site on the west side of the Metropolitan Museum of Art in 1881. The monument is easy to find by following any number of park trails that lead toward the southwestern side of the museum. The monument's name, Cleopatra's Needle," is somewhat of a misnomer. Inscriptions on the monument include the names Thutmose III and Rameses II from the 12th Century BC (more than 11 centuries before Cleopatra). The obelisk is carved from a single piece of red granite derived from a quarry at Aswãn, and weighs about 224 tons. The surface of the stone is heavily weathered, nearly masking the rows of hieroglyphs engraved on all sides. closeup heiroglyph Photographs taken near the time the obelisk was erected in the park show that the inscriptions were still quite legible. Cleopatra's Needle in Egypt 1880 The stone had lain in the Egyptian desert for nearly 3000 years but undergone little weathering. In a little more than a century in the climate of New York City, pollution and acid rain have heavily pitted its surfaces.” From: 3dparks.wr.usgs.gov/nyc/parks/loc1.html D. Soil forms from the weathering of rocks. 1. Composed of four parts: Inorganic: tiny fragments of weathered rock Organic: decayed remains of plants and animals. Organic part also called Humus. Makes soil dark colored and fertile. Creating humus: compost pile compost - Google Image Search Air Water (see text p.133) 2. The type of Soil that forms depends on a number of factors (see text p.135-137, 139 read aloud). 3. Over time a mature soil can form made of layers or Soil Horizons. Soil Profile [Diagram] (See text p.138) photo- soil profile Earth Science Interlude: Big Wave Surfing- Eddie Aiku TournamentHawaii http://www.youtube.com/watch?v=fcPsXrzwS3A&NR=1 http://www.youtube.com/watch?v=k2vkwy2vdP4 II Erosion: is the movement of sediments by gravity, water, wind, and/or ice. A. Gravity is the driving force of all erosion. (Gravity makes water/ice flow and wind blow) Mass Movement occurs when gravity transports sediment all by itself. Mass_Wasting.asf Types: 1. Creep: slow movement of sediments down a hill. (text p. 147) [Diagram] image: creep 2. Slumping: faster movement downhill. (text p. 146) 3. Landslides and Mudflows: are the fastest movement of sediment downhill. Very dangerous. landslide vidclip- Japan YouTube - La Conchita Landslide kayak landslide YouTube - Landslides B. Running Water, in streams and rivers, transports more sediment than any thing else! http://www.youtube.com/watch?v=vpmOl-_JAqg “Water is the main agent of erosion on Earth.” image of medium sized stream 1. Stream Velocity is how fast the water is flowing. The greater the slope (or gradient) of the land, the greater the stream velocity. (text p.157) [Graph] Stream velocity is greatest in the center, a little below the surface. This is where friction is least (text p. 160) [Diagrams] 2. Stream Discharge is the amount (or volume) of water being carried. The greater the discharge, the greater the stream velocity (text p.161) [Graph] Amazon: image Congo: Google Image Result for http://www.socialstudiesforkids.com/graphics/congorivermap.jpg Yangtze: image Mississippi: http://www.mapofmississippi.com/images/maps.jpg C. Erosion by Flowing Water 1. Streams erode sediments in three ways: Ions (salts) dissolve and are carried in solution. Colloids, Clay, and Silt are carried in suspension (floating) Sand, and larger sediment bounce and roll along the bottom. This is called the Bed-Load. [Diagram] Fig. 10.14 - Modes of Sediment Transport 2. The greater the discharge, the greater the total sediment load transported. image mississippi river [Graph] Vidclip- stream erosion 3. The greater the velocity of a stream, the greater the size of the sediment eroded. (see ESRT p.6) esrt page 6 Practice: 4. The bed load can cut down through the stream bottom forming V-shaped canyons. v shaped valley - Google Search Case Study: The Grand Canyon grand canyon - Google Search [Diagrams] http://www.youtube.com/watch?v=ktf73HNZZGY&feature=related YouTube - Grand Canyon Adventure: River at Risk IMAX Trailer vidclip- Grand Canyon C. Erosion by Ocean Waves 1. Waves erode rocky shorelines to form cliffs, sea arches, and sea stacks. (text p.464- read). 2. On sandy beaches, sediment is transported by Longshore Drift. See Text p. 463-464 [Diagram] YouTube - Longshore Drift 1 YouTube - Longshore Drift Case Study: Long Island South Shore http://www.fireislandmgm.com/00fi_beach.jpg http://www.lib.utexas.edu/maps/national_parks/fire95.jpg http://www.loving-long-island.com/image-files/fire-island-lighthouse-looking-west.jpg http://lighthousegetaway.com/lights/NY/fire2.jpg [Diagram] Google Maps- Long Isand South Shore Wave erosion_ See ESRT p.6: 1. State the name of the maximum size particle that can be transported by a stream moving at 400 cm./s. 2. State the name of the maximum size particle that can be transported by a stream moving at 200 cm./s. 3. State the name of the minimum size sediment that can be transported by a stream moving at 200 cm./s. D. Erosion by Wind is most important on beaches and deserts. 1. Sediment often deposited in Dunes. (See Text p. 205-207) 2. Wind blown sediment can carve rock into strange shapes. Ex. “Hoodoo’s” [Diagram] wind erosion 1 wind erosion 2 wind erosion 4 vidclip: Wind Erosion 1 vidclip: Wind erosion 2 E. Erosion by Ice 1. Glacier: a mass of ice, formed on land, that slowly flows down hill. (See text p. 187-198) Vidclip- glaciers 1 Glaciers form when snow does not completely melt in summer and builds up from year to year. Two Types: Alpine or Valley Glaciers: form in mountains and flow slowly downhill. (Text p.187,188, 190) glacier Images alpine glacier 1 vidclip- lame lapse valley glacier [Diagram] Flowing ice carves V-shaped river valleys into a U-shape. (text p.193) [Diagram] Image U shaped valley 1 u shaped valley 2 u shaped valley 4 Continental Glaciers are huge sheets of ice that cover all or part of a continent. (text p. 189, 198) [Diagram] glacier Animations and Movies: cross section 2. Glaciers erode sediments of all sizes. Some sediments are carried on top. (text p.195) Some rocks freeze into the sides or bottom of ice. These often scratch and polish the underlying bedrock. (text p.,192). glacial straitions central park [Diagram] vidclip- glaciers 2 III Deposition: the laying down of sediments in a new location. A. Factors Effecting Deposition in Water 1. Larger particles, settle faster than smaller particles. [Diagram: Graphs] 2. Smallest particles may stay in suspension (floating) or solution (dissolved) and never settle. 3. If unsorted particles ( a mixture of sizes) are added to water… Largest (most coarse)will settle on bottom... and smallest (most fine) on top. [diagram: vertical Sorting] This is called Vertical Sorting or Graded Bedding. graqded bedding 1 graded bedding 2 graded bedding 3 4. When a stream enters a lake or ocean, it slows down and deposits sediment. Largest particles are close to shore finest are furthest from shore. This is called Horizontal Sorting. animation Observe how sediments are deposited. [diagram] 5. Denser particles, settle faster than less dense particles. 6. Rounder particles settle faster than flatter particles. [Diagrams: Sorting by Shape] [Graphs] 7. Life History of a Stream Youthful near the Source. (See text p.157,167) Steep slope, (high gradient) High velocity, Many rapids and waterfalls. Bed load cuts steep V-shaped valleys [Diagrams] youthful 1 youthful 2 youthful 3 Mature Stage (see text p.163) Less slope, less velocity Greater Discharge Greater sediment load (text p.165) Wide curves called Meanders form. [Diagrams:erosional/depositional systems] mature 1 mature 2 mature 3 YouTube - Sticky - One Minute on Meanders Old Age Stage (text p.168) Very low gradient (slope) Very high discharge Very high sediment load Ox-Bow Lakes or Bayou’s form. [Diagrams] old age 1 old age 2 old age 3 animation Meander Cut-Offs and Oxbow Lakes 8. Delta’s form when a stream or river enters a lake or ocean. (see text p.166) [Diagram] delta 1 mississippi delta 2 mississippi river delta 3 The_Mississippi_Delta_asf.asf C. Wind deposited sediments are often Angular [dia] show cross bedding. [Diagram] D. Evidence of Deposition by Ice 1. Sediments deposited by glaciers are angular (have sharp corners) and are poorly sorted (mixed up sizes). These deposits are called Glacial Till. (see text p.194) [Diagram] image glacial till glacial till 2 glacial till 3 2. Long hills of glacial till mark furthest advance of glacier. These called Terminal Moraines. moraine 1 moraine 3 3. Flat sandy areas, deposited by streams flowing from melting glaciers called Outwash Plains outwash plain 1 outwash plain 2 outwash plain 3 4. Many lakes form from melting blocks of ice. glacial lake 2 glacial lake 3 5. Large boulders dropped by melting ice called Glacial Erratics [Diagram] erratic 1 erratic 3 E. Glacial Features of Long Island [diagram] LI moraines view of Ronkonkoma moraine Ronkonkoma moriane- Montauk Ronkonkoma moriane 2 F. Other glacial landforms: see text p.193,197 YouTube - Glacial Erosion Landforms