EROSION- The transport of weathered materials…

Major Erosive Agents: Running Water GLACIERS WIND OCEAN CURRENTS AND WAVES MASS 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. unsaturated Vegetation – amount of plants Slope 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 Channel Fastest – middle just below surface

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.

The velocity changes in the S-shaped curves called MEANDERS. Fastest on the outside of the curve – erosion Slowest 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 outside Moves 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:

EROSION 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

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       Small

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

SEDIMENTS ERODED BY RUNNING WATER WILL BE … SORTED – all materials are about the same size