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Mechanical (physical) Weathering
• The process of breaking down sediment without changing the rocks chemical composition.
• Frost wedging
Exfoliation (Mechanical Weathering)
• Uplift of under rock causes the top hard rock, like granite, to split into layers.
Acids (chemical weathering)• Old tombstones made of marble will weather
due to the Carbonic Acid that is in rainwater.
Where does chemical weathering occur the fastest????????????
• WarmWarm and MoistMoist!!!!!!– Tropical rainforest
Where does Where does mechanicalmechanical weathering occur the fastest???weathering occur the fastest???
• Wet & temperate (warm day / cold night)
• Frost Wedging!!!!!
Buffalo, NY
Deposition
• When water flows downhill or wind slows down it loses energy of motion, & drops its sediments.
Large Sediment
Med Sediment
Small Sediment
http://www.classzone.com/books/earth_science/terc/content/visualizations/es1303/es1303page01.cfm?chapter_no=visualization
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.
Slump
• occurs when loose materials or rock layers slip downward as one large mass. It happens because the material under the slump weakens.
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.
Rockslides
• occur when large blocks of rock break loose from steep slopes and tumble quickly to the bottom.
• Fastest form of Mass Movement
Talus
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.
• 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.
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
LoessLoess• very fine sediment particles eroded by very fine sediment particles eroded by
wind that become packed together, wind that become packed together, creating a thick deposit. They are found creating a thick deposit. They are found in the farmlands of the U.S., especially in the farmlands of the U.S., especially the Mississippi River area.the Mississippi River area.
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
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.
Rill Erosion
Begins when a small stream forms after a heavy rain. Water can carry away plants & soil, leaving a scar.
Gully Erosionbegins when a rill channel becomes broader & deeper. Large amounts of soil are removed from the area.
Alluvial Fan
a type of deposit shaped like a triangle that occurs when a river drops sediments on a floodplain. (land)
Delta
A type of Alluvial fan when the sediments are into a large body of water (lake, gulf or ocean)
ex. (Mississippi delta)
Things people can do to reduce erosion
Build terraces. Terraces are broad, step-like cuts made
into the side of a
slope.
Things people can do to reduce erosionThings people can do to reduce erosion
Plant vegetationPlant vegetation
No till farmingNo till farming
Wind Breaks (fences/trees)Wind Breaks (fences/trees)
Video - dustbowlVideo - dustbowl
• Erosion can be slowed, but never stopped Erosion can be slowed, but never stopped completely.completely.
River systems are referred to as dendtritic, like tree branches.
Small streams branching off of larger streams.
Tributaries
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).
Stream Characteristics
GradientGradient: The slope or steepness of a stream channel. Affects stream velocity and bedload (sediment deposition) size.
Discharge• The amount of water passing a point over a period
of time.
Which has a greater discharge?
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.
Mature Rivers
– Mature rivers flows down a more gradual slope with curves called meanders.
The floodplain
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.
Quiz – Water/Wind/Glacier Erosion
1. The beginnings of a stream is called a _.
2. Name the largest gully.
3. What is an Alluvial Fan?
4. Glaciers form this shape valleys.
5. Pieces of rock picked up by wind is called ____.
6. Name two methods of reducing erosion’s affects.