REVIEW
What is WEATHERING?
Def:
The breakdown of rocks at or
near Earth’s surface
There are 2 types of WEATHERING:
1. CHEMICAL
2. PHYSICAL
CHEMICAL WEATHERING
EXAMPLES:
1. OXIDATION (rust)
CHEMICAL WEATHERING
EXAMPLES:
2. WATER– the universal solvent
Slowly dissolves rocks. Will happen faster when there’s
acid present (remember the fizzing)
physical
WEATHERING
EXAMPLES:
1. FROST ACTION
2. PLANT ROOTS
3. ABRASION
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)
So that’s WEATHERING, what’s EROSION?
Weathering occurs IN PLACE
Involves the TRANSPORT of sediments.
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
The DRIVING FORCE behind most types
of EROSION is
GRAVITY
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……
Oh no!
Gravity erosion can happen very quickly or very
slowly, depending on the conditions.
“Soil creep” happens very
slowly (less than 1 cm per
year).
Soil gradually moves
downhill
Landslides can be quite
destructive:
Rate = 1 mm/day to 100 km/hr
Houses can be totally covered by
sand and mud, like this:
Mud Flows are usually
caused by the friction
holding the rock in place
being reduced by the
presence of water.
THE PROBLEM WITH
LANDSLIDES AND
MUDSLIDES IS THAT
THEY ARE OFTEN
UNPREDICTABLE AND
CAN BE VERY
DAMAGING TO LIFE AND
PROPERTY
This landslide tragically took the life of many unsuspecting woodland creatures.
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
WATERSHEDS / DRAINAGE
BASINS
Def: The area of land drained by any one stream
REMEMBER: a stream is running water that’s confined to a
channel---this channel can be any size:
MEDIUM
LARGE
SMALL
Q:Where 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)
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
Washingto
nville in?
The US is divided into watersheds also:
THE MISSISSIPPI RIVER WATERSHED
is the biggest (OBVIOUSLY)
The UNITED STATES is split into two LARGE drainage basins.
This side, all water flows to
ATLANTIC OCEAN
This side, all water flows to
PACIFIC OCEAN
STREAMS
Running water is the most common agent of erosion on Earth’s surface.
THE
WATER
CYCLE!
HOW DOES THE WATER GET
INTO A STREAM?
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.
B
A
The smaller streams
are called tributaries.
Different streams flow at different
velocities (speeds)
WHY?
GRADIENT! B
A
C
Would a stream flow faster from A to B or from A to C?
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
Water flows at different speeds within the same stream.
WHY?
FRICTION
The water that is in contact with the sides and bottom of the stream
channel will be slowed by friction and will therefore move SLOWER.
Water flows differently around curves
than it does in a straight line
Because of this, water flows at different
speeds within the same stream.
Moves slowly
Movesaround
faster around
the inside
the outside
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).
Here’s a picture:
DEPOSITION
EROSION
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
YOUNG streams
flow over a
steep gradient
and tend to be
relatively
small.
As they flow
they carve out
a V-shaped
valley
Notice the VERY steep sides
Waterfalls
indicate a
YOUNG
stream
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:
MEANDER
faster around the outside of the
erode more sediment, gradually
Because water moves
meander it is able to
carving out a bigger and bigger meander:
Eventually,
water breaks
However, the channel full of water is still there, so
across the
it becomes an OXBOW LAKE
banks and
cuts off the
old channel.
This process
creates an
OXBOW LAKE
Why
“Oxbow”?
THE GRAND CANYON WAS
FORMED BY STREAM EROSION
Eventually all
streams flow
into the ocean.
This part of a
stream is called
a DELTA