REVIEW

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REVIEW
What is WEATHERING?
Def The breakdown of rocks at or near
Earths surface
There are 2 types of WEATHERING
1. CHEMICAL
2. PHYSICAL
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CHEMICAL WEATHERING
EXAMPLES
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CHEMICAL WEATHERING
2. WATER the universal solvent
EXAMPLES
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physical WEATHERING
EXAMPLES
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FACTORS THAT AFFECT THE RATE AND TYPE OF
WEATHERING
1. EXPOSURE (rocks need to be exposed to
weathering agents in order to erode)
2. PARTICLE SIZE (the smaller the particles, the
greater the surface area)
3. MINERAL COMPOSITION (different minerals
weather at different rates more on this later)
4. CLIMATE (the temperature and the amount of
water present will determine the amount and type
of weathering that can occur)
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So thats WEATHERING, whats EROSION?
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EROSION
The process by which sediments are obtained and
transported.
Erosion involves a transporting system with
several components

1. AGENT OF EROSION- (e.g. stream, glacier, wave,
   current, wind, or human activity).

2. SEDIMENTS BEING MOVED
3. DRIVING FORCE
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The DRIVING FORCE behind most types of EROSION is
GRAVITY
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GRAVITY EROSION

• Gravity always pulls down on all objects.

• Friction opposes the force of gravity, keeping
  objects in place

• Usually these two forces are in EQUILIBRIUM
  (balance), however sometimes..

• The force of friction decreases, and gravity
  overtakes friction

When this occurs, bad things can happen
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Gravity erosion can happen very quickly or very
slowly, depending on the conditions.
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In real life, landslides can be quite destructive
Rate 1 mm/day to 1 km/hr
Houses can be totally covered by sand and mud,
like this
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Mud Flows happen faster (1-5 km/hr)
THE PROBLEM WITH LANDSLIDES AND MUDSLIDES IS THAT
THEY ARE OFTEN UNPREDICTABLE AND CAN BE VERY
DAMAGING TO LIFE AND PROPERTY
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This landslide tragically took the life of many
unsuspecting woodland creatures.
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The final form of gravity erosion occurs when
rocks weather at a higher elevation and fall to a
lower elevation. This is called, (you guessed
it), a Rock Fall
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WATERSHEDS / DRAINAGE BASINS
Def The area of land drained by any one stream
REMEMBER a stream is running water thats
confined to a channel---this channel can be any
size
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QWhere does water go once it hits the surface of
the earth? A Some gets absorbed into the ground
(infiltration) some flows along the surface
(runoff)
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The rivers of New York State obtain their water
from very distinct regions. The state is divided
into the following DRAINAGE BASINS (WATERSHEDS)
These watershed regions are pretty small because
the streams they feed into are pretty small
What Drainage basin is Washingtonville in?
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The US is divided into watersheds also
THE MISSISSIPPI RIVER WATERSHEDis the biggest
(OBVIOUSLY)
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The UNITED STATES is split into two LARGE
drainage basins.
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STREAMS
Running water is the most common agent of erosion
on Earths surface.
HOW DOES THE WATER GET INTO A STREAM?
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Water always flows from HIGH elevation to LOW
elevation.
Along the way, this water combines with other
water, so the size of the stream gets bigger and
bigger.
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Different streams flow at different velocities
(speeds)
WHY?
GRADIENT!
Would a stream flow faster from A to B or from A
to C?
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The speed at which a stream flows will determine
what size sediments it can carry

• Fast moving water can carry larger sediments
  (duh)

Big ? ? ? ? ? ? Small
Slow ? ? ? ? ? ? ? ? Fast
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Water flows differently around curves than it
does in a straight line
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Because of this, water flows at different speeds
within the same stream.
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This means that around the outside of curves,
since the water is moving faster, it will be able
to erode more and larger particles.
The opposite is also true, since the inside of
curves are moving more slowly, some of the
particles the water carries will be deposited
(dropped).
Heres a picture
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DEPOSITION
EROSION
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Streams that exist in hilly or mountainous
regions slowly erode sediment over time
The goal of every stream is to make the land
FLAT. This takes time (as in MILLIONS of years)
The FLATTER the land, the OLDER the stream
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YOUNG streams flow over a steep gradient and tend
to be relatively small.
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Notice the VERY steep sides
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Waterfalls indicate a YOUNG stream
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As time goes by, the stream erodes away the land
and makes it flatter. When the gradient is low,
the shape of the stream changes and meanders form
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faster
Because water moves around
the outside of the meander it is able to
more sediment, gradually carving
out a bigger and bigger meander
erode
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Eventually this meander gets so big and
exaggerated that it is cut off from the
stream.
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THE GRAND CANYON WAS FORMED BY STREAM EROSION
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Eventually all streams flow into the ocean