Transcript EROSION- The transport of weathered materials… Major Erosive Agents:  Running Water  GLACIERS  WIND  OCEAN CURRENTS AND WAVES  MASS WASTING (GRAVITY!)

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
1995
Landslide in
La Conchita,
CA.
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.
New York City’s
Henry Hudson
Parkway in
Upper
Manhattan
A 75 foot
retaining wall
collapsed on
May 12th, 2005.
Running water move more
sediment than any other
agent of erosion.
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. unsaturated
 Vegetation – amount of plants
 Slope 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
3 factors affecting
Stream Velocity
 Gradient – slope of the stream
 Discharge – volume of water
 Stream channel shape
Stream Velocity in a Straight Channel
Fastest – middle just below surface
The velocity changes in the S-shaped curves
called MEANDERS.
Fastest on the outside of the curve – erosion
Slowest on the inside of the curve - deposition
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)
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
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 deposition
Cut 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?
Levee Formation
SEDIMENTS ERODED BY
RUNNING WATER WILL HAVE
THESE CHARACTERISTICS
 ROUNDED and SMOOTH
 SORTED 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 smaller
 Arid 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