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Mechanical (physical) Weathering
The process of breaking down sediment without changing the rocks chemical composition. Frost wedging
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Physical Weathering To view this animation, click “View” and then “Slide Show” on the top navigation bar.
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Biological activity (Mechanical Weathering) –(sometimes chemical)
Tree roots splitting rock
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Biological activity
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Exfoliation (Mechanical Weathering)
Uplift of under rock causes the top hard rock, like granite, to split into layers.
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Thermal Heating & Contraction
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Chemical Weathering The transformation of rock into one or more new substances.
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Oxidation
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Chemical Weathering Oxidation : Elements reacting with Oxygen
ex. (Rust)
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Hydrolysis
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Feldspar +Water = Clay Feldspar A Clay Cliff
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Acids
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Lichen – Plant Acid
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Sulfuric Acid & Carbonic Acid
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Acids (chemical weathering)
Old tombstones made of marble will weather due to the Carbonic Acid that is in rainwater.
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Dissolution Dissolving a rock in water
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Carbonation
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What can affect Mechanical and Chemical Weathering?
Dissolving candy!!!! – I need a volunteer
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Where does chemical weathering occur the fastest????????????
Warm and Moist!!!!!! Tropical rainforest
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Where does mechanical weathering occur the fastest???
Wet & temperate (warm day / cold night) Frost Wedging!!!!! Buffalo, NY
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Erosion – The process of moving weathered sediments from one location to another.
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The four major Agents of Erosion are:
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Gravity (Mass Movement)
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Running Water
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Wind
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Glaciers
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Types of Mass Movement (Gravity)
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Water erodes more sediments than any other agent of erosion, due to its great energy of motion.
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Deposition When water flows downhill or wind slows down it loses energy of motion, & drops its sediments. Large Sediment Med Sediment Small Sediment
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Mass Movement Gravity causes loose materials to move down a slope. When gravity alone causes materials to move down slope this erosion is called Mass Movement.
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Mass Movements: Five Main Types
To view this animation, click “View” and then “Slide Show” on the top navigation bar.
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Slump occurs when loose materials or rock layers slip downward as one large mass. It happens because the material under the slump weakens.
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Creep occurs when sediments slowly move downhill. As the ground freezes, small sediments are pushed up by the expanding water in the soil. As it thaws, the sediments fall down slope, often less than a millimeter at a time.
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Rockslides occur when large blocks of rock break loose from steep slopes and tumble quickly to the bottom. Fastest form of Mass Movement Talus
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Mudflows usually occur in relatively dry areas where weathering forms thick layers of dry sediments. When heavy rains or rapid ice thawing happens, water mixes w/ the sediments & forms a thick mud. Gravity causes this mud to flow downhill.
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All types of Mass Movement happen where there are slopes
All types of Mass Movement happen where there are slopes. All are more likely to happen after a heavy rain because water makes the sediments heavier & slippery.
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Wind Erosion
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Areas most prone to wind Erosion
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Deflation wind picking up and moving small sediments such as clay, silt, and sand.
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Sediment Transport by Wind
To view this animation, click “View” and then “Slide Show” on the top navigation bar.
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Abrasion wind making sand grains roll and skip, bumping into other grains and rocks. The surfaces they strike become pitted and polished when small fragments are broken off. (sandblasting) Glen Canyon, AZ
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Wind Deposition Loess Dunes
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Loess very fine sediment particles eroded by wind that become packed together, creating a thick deposit. They are found in the farmlands of the U.S., especially the Mississippi River area.
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Dunes sediments blown by wind that encounter a barrier such as a plant, rock or some other obstacle and pile up behind it. These are the most common type of wind deposits. Small scale
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Large scale
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Dune Movement
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Running Water Erosion
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Sheet Erosion Occurs when rainwater flows over a relatively flat area to lower elevations carrying sediments with it. The sediments left behind cover the soil like a sheet.
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Rill Erosion Begins when a small stream forms after a heavy rain. Water can carry away plants & soil, leaving a scar.
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Gully Erosion begins when a rill channel becomes broader & deeper. Large amounts of soil are removed from the area.
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Most Famous Gully Grand Canyon
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Sediment Transport by Streams
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Alluvial Fan a type of deposit shaped like a triangle that occurs when a river drops sediments on a floodplain. (land)
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Delta A type of Alluvial fan when the sediments are into a large body of water (lake, gulf or ocean) ex. (Mississippi delta)
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Vegetation Affects Erosion
Roots hold soil in place!!!!!!!!!!!!!!!!!!!!!!!!!
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Things people can do to reduce erosion
Build terraces. Terraces are broad, step-like cuts made into the side of a slope.
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Things people can do to reduce erosion
Plant vegetation No till farming Wind Breaks (fences/trees) Video - dustbowl
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Erosion can be slowed, but never stopped completely.
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Rivers
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River systems are referred to as dendtritic, like tree branches.
Tributaries Small streams branching off of larger streams.
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Where do streams get their water supply?
Surface water runoff Groundwater (base flow) Water has to go somewhere! It always follows the path of least resistance (generally downhill).
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Drainage basin the land area from which a stream gets its water.
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Mississippi Drainage Basin
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Stream Characteristics
Gradient: The slope or steepness of a stream channel. Affects stream velocity and bedload (sediment deposition) size.
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Discharge The amount of water passing a point over a period of time.
Which has a greater discharge?
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Stages of Stream Development
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Erosion of Deformed Sedimentary Rock
To view this animation, click “View” and then “Slide Show” on the top navigation bar.
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Stages of River Development
Young streams flow fast through steep valleys. They are found in mountainous or hilly regions and may have white water rapids and waterfalls. They have high levels of energy and erode the stream bottom more than the sides.
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Mature Rivers Mature rivers flows down a more gradual slope with curves called meanders. The floodplain
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Old-stage rivers flow very slowly through a very broad, flat floodplain that is curved.
A river in this stage mostly erodes its sides causing changes in its meanders, like the Mississippi. Meanders can eventually be cut off forming Oxbow lakes.
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Erosion of Deformed Sedimentary Rock
To view this animation, click “View” and then “Slide Show” on the top navigation bar. 85
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Meanders (old rivers)
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Meanders
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Old Mississippi Meander
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Oxbow Lakes (Old Rivers)
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Oxbow Lake Formation
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Young stream Mature stream Old stream
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Quiz – Water/Wind/Glacier Erosion
The beginnings of a stream is called a _. Name the largest gully. What is an Alluvial Fan? Glaciers form this shape valleys. Pieces of rock picked up by wind is called ____. Name two methods of reducing erosion’s affects.
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Shoreline and Sedimentation Changes
To view this animation, click “View” and then “Slide Show” on the top navigation bar. 93
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