erosion-
DESCRIPTION
EROSION-. The transport of weathered materials…. Major Erosive Agents:. Running Water GLACIERS WIND OCEAN CURRENTS AND WAVES MASS WASTING (GRAVITY!). EROSION by gravity. Also known as MASS MOVEMENT Avalanches or rock falls Land or Mud Slides Slump or Flows Creep. - PowerPoint PPT PresentationTRANSCRIPT
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EROSION-
The transport of weathered materials…
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Major Erosive Agents:
Running WaterGLACIERSWINDOCEAN CURRENTS AND
WAVESMASS WASTING (GRAVITY!)
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Also known as MASS MOVEMENTAvalanches or rock fallsLand or Mud SlidesSlump or FlowsCreep
EROSION by gravity
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1995 Landslide in La Conchita, CA.
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The two forces involved in all mass movements are GRAVITY (pulling the material down) and FRICTION (keeping the material in place).
Typically excessive amounts of water lessen the force of friction and lead to a landslide.
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New York City’s
Henry Hudson
Parkway in
Upper
Manhattan
A 75 foot
retaining wall
collapsed on
May 12th, 2005.
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Running water move more sediment than any other agent of erosion.
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What happens to rainfall when it hits earth????
Some evaporates Some is absorbed and becomes ground
water Some is run off
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What determines if rainwater becomes runoff or groundwater?
Ground Conditions:Saturated vs. unsaturatedVegetation – amount of plantsSlope or Gradient of the Land
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Running Water – Most of North America is above sea level. Water flows high to
low sea level due to gravity
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When Runoff becomes confined to a channel – Stream Exists
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Watersheds or Drainage Basins
Smaller stream that flows into a larger stream is called a tributary
Tributaries and land that contribute to the stream is called a drainage basin or watershed
(COMPARED TO A BATHTUB. WATER THAT COLLECTS IN A BATHTUB FLOWS TOWARD THE DRAIN.)
The drainage basin of one stream is separated by a drainage divide (ridges or mountains – higher elevations)
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HOW WATERSHEDS/DRAINAGE BASINS FORM – RED LINE IS DRAINAGE DIVIDE
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Watersheds: Continental Divide and Appalachian Mountains
Water goes from high sea level to low sea level
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Watershed Regions of New York State
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3 factors affecting Stream Velocity
Gradient – slope of the stream
Discharge – volume of water
Stream channel shape
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Stream Velocity in a Straight ChannelFastest – middle just below surface
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The velocity changes in the S-shaped curves called MEANDERS. Fastest on the outside of the curve – erosionSlowest on the inside of the curve - deposition
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STREAMS CARRY MATERIAL IN … Solution: dissolved material (includes
salts)
Suspension: particles carried in the flow of the water (Clay, silt, sand)
Bed load: particles carried by rolling, bouncing, or dragging along the stream bed (Pebbles, cobbles, boulders)
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THE GREATER THE VELOCITY OF A STREAM…
THE LARGER THE SEDIMENT PARTICLES IT CAN CARRY
THE MORE TOTAL SEDIMENTS IT CAN CARRY
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Water Velocity determines the size particle that can be moved via suspension and bed load
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Stream Development – Early Stage
The landscape is continuously being reshaped by stream erosion. Plateaus can be cut by rivers to form canyons. Valleys can be carved in mountains as rivers flow through them.
As the stream begins to down cut into the land – waterfalls and rapids form
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Stream Development – Young Stage
V-Shaped Valley Rapids and Waterfalls No Flood Plain – a level plain that borders
stream
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V-SHAPED VALLEY…
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RAPIDS AND WATERFALLS
Rapids - Different resistance among rocks cause FAST-FLOWING WATER
Waterfalls – Rapids develop into waterfalls as softer rock erodes
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Stream Development - Mature Stage Lateral erosion widens the valley
profile – slope decreases River meanders pronounced A FLOOD PLAIN develops
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As the stream grows larger – it begins to shift its course in a series of bends or curves called meanders seeking out the lowest elevation
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Point Bars show depositionCut Banks show erosion
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Cut bank on outside of curve due to higher velocity of water – more erosion
Cut bank on outside of curve
Point Bar on inside of curve
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Stream Development - Old Age
Very Wide Flood Plain Land worn down to flat surface Oxbow Lakes
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Stream Development – Old Age
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Eventually, it takes too much energy to keep meandering, so rivers will cut off a bend, resulting in an OXBOW lake…
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What is the correct sequence in stream development?
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Levee Formation
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SEDIMENTS ERODED BY RUNNING WATER WILL HAVE THESE CHARACTERISTICS
ROUNDED and SMOOTHSORTED AND LAYERED
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SEDIMENTS ERODED BY RUNNING WATER WILL BE … SORTED – all materials are
about the same size
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Contour lines showing head of the stream to the mouth of stream with delta
Velocity slows when entering a large body of water
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Alluvial fans form when streams come out of mountains onto flat land – velocity slows and deposition occurs
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Erosion by Waves and Long shore Current
Where lake or ocean waters meet land, waves and currents act as agents of erosion, creating unique landscape features
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Winds at the ocean’s surface cause waves
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Longshore Current
Waves are refracted or bent in the shallow water of the shore
Water near the shore is pushed in one direction along the shore – called longshore current
Sediments are carried in a zig-zag pattern in the SAME direction as the longshore current
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The sand trapping effect of the jetties to the north at Charleston, South Carolina has deprived Morris Island of needed sand. As a result, the island has eroded to the point that this previously land based lighthouse is now 400 meters out to sea.
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Which direction is the long shore current carrying sediment????
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Barrier Islands
Wave Action creates sand bars Waves and Longshore current - can
form barrier islands Ex. Fire Island
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Wind Erosion
Sediment – sand or smallerArid regions or ocean coastlines
2 types:
1. Deflation – lowers the land
2. Sandblasting and Abrasion
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Sandblasting and Abrasion Wind can only lift sand to about 1 meter
high - results in “Mushroom Rock” Frosted or Pitted sediments – rocks with
flat sides
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Windward side
Leeward side
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