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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 WEATHERINGEXAMPLES:
1. OXIDATION (rust)
CHEMICAL WEATHERINGEXAMPLES: 2. WATER– the universal
solventSlowly dissolves rocks. Will happen faster when there’s acid present (remember the
fizzing)
EXAMPLES:
physical WEATHERING
2. PLANT ROOTS
3. ABRASION
1. FROST ACTION
FACTORS THAT AFFECT THE RATE AND TYPE OF
WEATHERING1. 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.
EROSIONThe 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 isGRAVITY
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
Houses can be totally covered by sand and mud, like this:
Landslides can be quite destructive:
Rate = 1 mm/day to 100 km/hr
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
SMALL
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:
LARGE
MEDIUM
Topic 11D.1 -- Running Water - An Erosional-Depositional System I
A. Watershed or Drainage Basin = the entire area of land from which a stream and its tributaries receive water.
B. Divide = Imaginary line which separates the drainage basins of two separate streams.
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):
What Drainage basin is Washingtonville in?
These watershed regions are pretty small because the streams they feed into are pretty small
THE MISSISSIPPI RIVER WATERSHEDis the biggest (OBVIOUSLY)
The US is divided into watersheds also:
The Continental DivideThe 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
HOW DOES THE WATER GET INTO A STREAM?
STREAMSRunning water is the most common agent of erosion on Earth’s surface.
THE WATER CYCLE!
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.
A
B
The smaller streams are called tributaries.
Different streams flow at different velocities (speeds)
WHY?
GRADIENT!
A
C
B
Would a stream flow faster from A to B or from A to C?
• Fast moving water can carry larger sediments (duh)
The speed at which a stream flows will determine what size sediments it can
carry
Slow Fast
Big
Sm
all
Stream Velocity in a Straight Channel
Water flows at different speeds within the same stream.WHY? FRICTIO
NThe 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 faster around the outsideMoves slowly around the inside
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
ErosionEROSION
DEPOSITION
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
Because water moves around the outside of the
meander it is able to more sediment, gradually
carving out a bigger and bigger meander:
fastererod
e
Eventually, water breaks
across the banks and
cuts off the old
channel.
This process
creates an
OXBOW LAKE
Why “Oxbow”?
However, the channel full of water is still there, so it becomes an OXBOW LAKE
THE GRAND CANYON WAS FORMED BY STREAM EROSION
Eventually all streams flow
into the ocean.
This part of a stream is called a
DELTA