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 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