Aim: How does running water cause erosion?

I. Erosion by running water

A. Water breaks up bedrock and removes weathered and eroded rocks and soil materials.

1. Uses sand, pebbles, and boulders as cutting tools.

2. Abrasion – grinding action of sediments against one another and bedrock.

3. Rapidly moving water has a lifting effect that splits off and moves rock fragments.

4. Water chemically breaks down soluble minerals that hold sedimentary rocks together.

B. Water removes weathered rock

1. Rivers carry rock material in 3 ways:

a. SolutionSolution – material that has dissolved from bedrock (most common are compounds of magnesium and calcium)

b. SuspensionSuspension – material that includes clay, silt, and fine sands. Creates muddy water effect.

c. Bed load – materials that are too heavy to be carried in suspension (pebbles, sand, and boulders).

Composition of rivers in U.S. – 25% solution, 50% suspension, and 25% bedloads.

II. Carrying PowerCarrying Power – the total amount of sediment in a stream together with the size of the particles being moved by the stream.

A. Carrying power depends upon speed of stream and discharge.

1. DischargeDischarge – is the volume of water flowing past a given point in the stream at a given time. (m3/sec or ft3/sec)

http://www.geo.wvu.edu/~donovan/geol101/animations/15.swf

Bedloads, suspensions, and solutions