EROSION-

The transport of weathered materials…

Major Erosive Agents:

Running WaterGLACIERSWINDOCEAN CURRENTS AND

WAVESMASS WASTING (GRAVITY!)

What happens to rainfall when it hits earth????

Some evaporates Some infiltrates the soil and becomes

groundwater Some becomes runoff

What determines if rainwater becomes runoff or groundwater?

Ground Conditions:Saturated vs. unsaturatedVegetation – amount of plantsSlope or Gradient of the Land

When Runoff becomes confined to a channel – Stream Exists

3 factors affecting Stream Velocity

Gradient – slope of the stream

Discharge – volume of water

Stream channel shape

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?

Stream Velocity in a Straight ChannelFastest – middle just below surface

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.

The velocity changes in the S-shaped curves called MEANDERS. Fastest on the outside of the curve – erosionSlowest on the inside of the curve - deposition

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 larger

particles

The opposite is also true, since the inside of curves are moving slower, some of the

particles the water carries will become too big and will be

deposited.Here’s a picture:

Deposition

ErosionEROSION

DEPOSITION

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

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

Stream Velocity and Carrying Capacity• 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

SEDIMENTS ERODED BY RUNNING WATER WILL HAVE THESE CHARACTERISTICS ROUNDED and SMOOTHSORTED AND LAYERED

SEDIMENTS ERODED BY RUNNING WATER WILL BE … SORTED – all materials are

about the same size