I. Running water:

1. Erosion:

a. most erosion on earth is due to running water (streams and rivers).

Image from http://www.northriveradventures.com/photos.htm

b. The velocity of the stream determines size of the sediments/particles that can be carried. See page 6 ESRT

Sediments are carried:• In solution: dissolved minerals/ions• floating: organic debris• suspension: silts, sands and colloids that give the stream the ‘dirty water appearance”• rolling/bouncing along the riverbed at a much

slower rate than the water velocity. These particles are large cobbles, and boulders

• c. The particles carried by running water become rounded and smooth due to the abrasion that occurs.

• Some chemical weathering also occurs, further softening the rock.

2. Deposition by Water:

• a. Streams drop sediments according to the size of the sediments

b. Streams slow down where:

• The mouth of the river enters the ocean (lake)• On the inside bends of rivers• During drought conditions, when volume

decreases• When the river runs across flat land.

c. The sediments will settle in water according to:

• Particle size in which the largest settle first.• Particle shape ; round particles settle fastest

because there is less friction• Particle density, in which the most dense

settle the fastest, such as gold.

These factors create particle sorting:

• Horizontal sorting occurs when rivers enter lakes or oceans.

• Vertical sorting occurs when rivers repeatedly flood and return to normal stage.

3. Speed of the water

• Channel shape, slope or gradient, and volume of the water determine the speed of the water at any given point.

a. The shape of the channel:

• ‘meanders’ are bends in a river. • The water that hits the outside of the bend is

fast and causes more erosion of the banks.• The water that travels across the inside bend

is slower (more deposition)

Repeated flood events exacerbate the alternate erosion and deposition, and the curves become more pronounced, eventually looking like the Mississippi

b. In a straight channel,

• created in fast-moving, young rivers moving across steep ground,

• erosion is downward , • and the river channels are deep.

• The channel shapes are changed by the interplay of erosion and deposition,

• which cause the water to change speed, and • that changes how much and where erosion

and deposition will occur.

Young River Mature River Old River