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Weathering, Erosion, Deposition Weathering • The breakdown of rocks into smaller particles Types of Weathering • Physical • Chemical Physical Weathering • Does not change the composition of the rock • Dominates in cold/ moist climates • Creates more surface area Frost Wedging • Occurs in climates with freezing and thawing temperatures – Ex pot holes Root action • Roots grow into and under rocks • Roots pry the rock apart – Ex. Cracks in the sidewalk Abrasion • Bumping and rubbing of rocks as they collide • Rocks become smaller, smoother, rounder Exfoliation • Surface of the rock peels off – Unloading- caused by uplift and exposure of rock that was once deep underground – Decreases pressure on the rocks Chemical Weathering • Changes the composition of the rocks • Dominates in warm moist climates • Occurs on the surface of rock materials Types of chemical weathering • Oxidation • Carbonation • Hydration oxidation • Iron atoms combine with oxygen to form iron oxide (rust) carbonation • Carbonic acid in rain causes minerals to dissolve – Marble gravestones hydration • Water weakens the rock and the rock crumbles – Feldspar becomes clay Composition of rocks • Weaker, less resistant rocks weather away faster than other rocks • In the diagram, shale (layer A) is less resistant than the other rocks Factors that Effect Weathering Factor Physical Weathering Chemical Weathering Climate Cold and moist Warm and moist Exposure -Creates more surface area where weathering can occur -longer exposure means more weathering -occurs on the surface where the rock is exposed to the atmosphere or hydrosphere Composition - Weaker rocks are less resistant and weather faster (break easily) -weakens the minerals in the rock so that it breaks easier Dominant type of weathering graph • Weathering, Erosion, Deposition Quiz 1 • 1) What are the two types of weathering? • 2) What are the types of physical weathering? • 3) Describe the location where frost wedging occurs. I do NOT want a location. • 4) What type of weathering is present below? • 5) What type of weathering is present below? • 6) During which type of weathering is the composition of the rock unchanged? • 7) During which type of weathering is the composition of the rock changed? • 8) In what type of climate is physical weathering most common (dominant)? • 9) In what type of climate is chemical weathering most common? • 1) What are the two types of weathering? Physical and Chemical • 2) What are the types of physical weathering? Frost wedging Root action Abrasion exfoliation • 3) Describe the location where frost wedging occurs. I do NOT want a location. The location must be cold enough for water to freeze but warm enough for the ice to melt • 4) What type of weathering is present below? Exfoliation I guess physical weathering • 5) What type of weathering is present below? Root action • 6) During which type of weathering is the composition of the rock unchanged? Physical weathering • 7) During which type of weathering is the composition of the rock changed? Chemical weathering • 8) In what type of climate is physical weathering most common (dominant)? Cold/moist climates • 9) In what type of climate is chemical weathering most common? Warm/ moist climates Example of weathering and erosion over time… Appalachian Mountains Currently • highest peak of the Appalachians of 6,684 feet (Mount Mitchel), • the Rockies highest peak is 14,440 feet (Mount Elbert) Some debate on how high they used to be… • 29,029 Soil • The result of weathering and biological activity over long periods of time I • Parent rock breaks down into smaller pieces (sediment) II • Organisms help break up the rocks as they go through the broken rock particles. Organic material is added to the rock particles when they die. III • The top layer (horizon A) is usually rich with organic matter. More growth of plants on the surface further weakens the rocks and adds organic material IV • The soil continues to form and minerals leach into the lower levels. Soil continues to thicken and develop • Dark brown to black soil with high organic content • Tan to orange soil with high clay content, some rock fragments • Light gray to black soil, coarse rock fragments Residual Soil • Soil is the same substance as the underlying bedrock • Soil formed and stayed in the same place Transported Soil • Soil is made up of completely different material than the underlying bedrock • Soil was moved or transported. Erosion • The transportation of weathered rock materials Agents of Erosion • • • • • Streams (running water) Glaciers (moving ice) Wave action Wind Mass movements (gravity) Deposition • The dropping out of weathered rock materials Factors that affect deposition • Velocity- as the transporting medium slows down, sediments begin to settle out Factors that affect deposition • Shape: rounder particles settle faster than flatter particles Factors that affect deposition • Size: larger particles settle faster than smaller particles Factors that affect deposition • Density- most dense particles settle faster than less dense particles Sorting of Sediments • Sorted: larger, more dense, rounder particles settle out first. Sorting of Sediments • Unsorted sediments: sediments are dropped out in no order Sorted or unsorted? Sorted or unsorted? Horizontal Sorting • Occurs when a stream enters a large body of water • Velocity of stream slows down • Large particles settle out first http://hmxearthscience.com/Warehouse/geology/surface_processes/animations/horso rting.swf Vertical Sorting • Sorting of sediments from bottom to top • Largest, roundest, most dense particles settle out first and are on the bottom Graded Bedding • Series of depositional events that occurs at different times • You can count the events by counting the beds Graded bedding Horizontal or graded? Horizontal or graded? Horizontal or graded? Gravity • All agents of erosion are driven by gravity. • Examples of erosion by gravity alone including landslides dropping off cliffs and mass movement down steep slopes Running water • Most erosive agent • Gravity causes water to flow downhill • Sediments are weathered by abrasion and become smaller, rounder and smoother Running Water Cont. • The faster the water moves, the larger the particles it can transport • As the water slows down, the larger, rounder, more dense particles settle out first Running Water Ways in which sediment is carried: • Solution: sediments are dissolved • Suspension: sediments remain mixed in with water • Flotation: materials float on water • Bedload: sediments bounce on the bottom Ways in which sediment is carried Streams • Any body of water with a current – Brooks, creeks, tributary, river Velocity of a stream is influenced by… • 1. Gradient: the steeper the slope, the faster the water flows • 2. Volume: The greater the volume of water, the faster it flows – Discharge: volume of water Velocity of a stream is influenced by… • 3. Channel shape: water moves quickest through a straight smooth stream – Meander- a curve in a stream. • Water moves the fastest on the outside (erosion) • Water moves slowest on the inside (deposition) Velocity of a stream is influenced by… • 4. Large sediment: if a stream has a lot of large rocks, they will slow down the flow of water Stream Profiles Life of a Stream • Youth: – High energy – Fast moving – Steep gradient Life of a stream • Mature: – Gentler gradient – Slower moving water – Valley becomes wider than the river channel – Flood plains develop Life of a stream • Old Age: – Land is almost flat – May form oxbow lakes Deltas • As rivers enter a larger body of water they slow down • When streams slow down, _____________ happens. • When deposition exceeds the amount of sediment moved by waves and tides, deltas form Drainage Basin • Area where water from precipitation drains downhill into a body of water. Watershed • Area where water flows from • Surface water that feeds a river Tributary • A creek or stream that flows into a larger body of water Ocean Waves • Wave action rounds sediments as a result of abrasion • Shores are protected by sand dunes and barrier islands • Creates beaches: formed from weathering and erosion of continental and oceanic rocks • Forms sandbars: a ridge of sand, formed along a shore by the action of waves and currents – The protect barrier islands from erosion • Barrier island: a long narrow island, running parallel to the main land, made of sand. – Built up by the actions of waves, currents and wind that distribute the sand – Protect the coast from erosion • Waves approaching the shoreline: surf and tides move sand parallel to the shore within the zone of breaking waves. Glaciers • Large, very slow moving ice • Form in high latitudes and high elevations • Gravity causes glaciers to flow down a valley or spread out over a continent Glaciers cont. • Push, drag and carry sediments • Can carry any size sediments, including boulders • Depositon is unsorted • Features include striations (scratches) on the rock and parallel groves in the bedrock Valley Glacier Features • Form U shaped valleys • Glacial Till: unsorted sediment deposited by a glacier Things associated with Glaciers • • • • Boulders Striations U shaped valleys Unsorted sediment Finger Lakes • Formed by glaciers • When ice retreated deposits left behind dammed the stream valleys • Melt water filled the valleys • Direction of lakes show glacier movement through the former stream valleys Great Lakes • • • • • Formed at the end of the ice age Approximately 10,000 years ago Glaciers carved out the bedrock Glacial melt waters filled the basins Lakes contain approximately 20% of the worlds fresh surface water Wind Erosion • • • • Most common in arid (dry) climates Common in deserts and beaches Weathering by abrasion Surface features include dunes and sand blasted rock Wind direction by using dunes Landscape Regions • Forms from the interaction of crustal movement, type of bedrock, and climate • A-Mountain • B-Ridges • C-Plateau • D-Plain Geologic Factors that influence landscape • 1) crustal movement • 2) Type of bedrock • 3) Climate Drainage Patterns • Determined by the topography of the surface and the underlying bedrock Dendritic • • • • Most common stream pattern Tributaries seem to flow in the same direction Looks like branches on a tree Usually on undisturbed, horizontal rock layers Radial • Occurs when the stream flows away from a high point • Looks like spokes on a wheel • Develops over a smooth dome or volcanic cone annular • Occurs on an eroded dome • Appears to be a circular pattern with small tributaries going into each circle rectangular • Occurs where drainage flows along folds and faults • Looks like parallel lines with tributaries going into each path