erosion- the transport of weathered materials…
TRANSCRIPT
EROSION-
The transport of weathered materials…
Major Erosive Agents:
Running WaterGLACIERSWINDOCEAN CURRENTS AND
WAVESMASS WASTING (GRAVITY!)
What happens to rainfall when it hits earth????
Some evaporates Some is absorbed and becomes ground
water Some is run off
What determines if rainwater becomes runoff or groundwater?
Ground Conditions:Saturated vs. unsaturatedVegetation – amount of plantsSlope or Gradient of the Land
Running Water – Most of North America is above sea level. Water flows high to
low sea level due to gravity
When Runoff becomes confined to a channel – Stream Exists
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)
HOW WATERSHEDS/DRAINAGE BASINS FORM – RED LINE IS DRAINAGE DIVIDE
Watersheds: Continental Divide and Appalachian Mountains
Water goes from high sea level to low sea level
Watershed Regions of New York State
EROSION-
The transport of weathered materials…
STREAMS (the most important source of moving water…)
ALL streams flow * fill in the blank *
Streams begin at the HEAD and end at the MOUTH.
Streamflow is contained within a CHANNEL or STREAM BED
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)
3 factors affecting Stream Velocity
Gradient – slope of the stream
Discharge – volume of water
Stream channel shape
Stream Velocity in a Straight ChannelFastest – middle just below surface
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
THE GREATER THE VELOCITY OF A STREAM…
THE LARGER THE SEDIMENT PARTICLES IT CAN CARRY
THE MORE TOTAL SEDIMENTS IT CAN CARRY
Water Velocity determines the size particle that can be moved via suspension and bed load
Do Now:
Particle size worksheet
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
Stream Development – Young Stage
V-Shaped Valley Rapids and Waterfalls No Flood Plain – a level plain that borders
stream
V-SHAPED VALLEY…
RAPIDS AND WATERFALLS
Rapids - Different resistance among rocks cause FAST-FLOWING WATER
Waterfalls – Rapids develop into waterfalls as softer rock erodes
Stream Development - Mature Stage Lateral erosion widens the valley
profile – slope decreases River meanders pronounced A FLOOD PLAIN develops
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
Point Bars show depositionCut Banks show erosion
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
Stream Development - Old Age
Very Wide Flood Plain Land worn down to flat surface Oxbow Lakes
Stream Development – Old Age
Eventually, it takes too much energy to keep meandering, so rivers will cut off a bend, resulting in an OXBOW lake…
What is the correct sequence in stream development?
SEDIMENTS ERODED BY RUNNING WATER WILL HAVE THESE CHARACTERISTICS
ROUNDED and SMOOTHSORTED AND LAYERED
SEDIMENTS ERODED BY RUNNING WATER WILL BE … SORTED – all materials are
about the same size
Contour lines showing head of the stream to the mouth of stream with delta
Velocity slows when entering a large body of water
Alluvial fans form when streams come out of mountains onto flat land – velocity slows and deposition occurs
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
Winds at the ocean’s surface cause waves
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
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.
Which direction is the long shore current carrying sediment????
Barrier Islands
Wave Action creates sand bars Waves and Longshore current - can
form barrier islands Ex. Fire Island
Wind Erosion
Sediment – sand or smallerArid regions or ocean coastlines
2 types:
1. Deflation – lowers the land
2. Sandblasting and Abrasion
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
Windward side
Leeward side