Chapter 9

Surface water

Mars

Water- the most effective erosion agentRunning water-

Ex: rain, snow, rivers, lakes

Running water (RW) can erode rock in two ways

1.) Mechanical erosion and or 2.) Chemical erosion

1.) Mechanical erosion

a.) Abrasion- grinding action of sand, pebbles,even boulders used as cutting agents on one another by the force of moving water = rounded edges and smooth surfaces.

Petoskey stones

2.) Chemical Erosion

(RW) easily dissolves soluble minerals ex: Limestone, marble, sandstone,

Potholes chemical erosion may dissolve large pits in a river bed and mechanical erosion may scour out a bowl-like basin

Rivers carry rock in three ways = stream load

1.) Soluble minerals are dissolved in “solution” (dissolved load)

Dissolved load

2.)Suspended load: Small particles of

Suspended load

3.) Larger particles=

Dissolved load

Suspended loadBed Load

turbulence

Estimation: U.S rivers carry their stream load: ¼ dissolved load ½ Suspended Load and ¼ Bed Load

Stream carrying power =

•Velocity depends on

Flood stage= tremendous increase in volume and depth of water which increases velocity, therefore the carrying power of the river can be increased hundreds of times

•1.) Rivers do most of their erosional change at this stage•2.)They usually remove all sediments from floor and dig deep into bedrock ex: Mississippi river

River Valleys

1.) Young rivers-

Also, upper valley walls widen by weathering and erosion.

2.) Mature (old)

Canyons= valleys with steep, almost vertical sides (AKA) Gorges or Chasms

•Erosion from rains form small valleys (gullies) and/or small rivers. If rain stops, gullies remain. Next rain, gully grows in length, depth, and width=

Divides- High land separating one gully or river from the next

River system- a river and all of its tributaries.

Water shed (drainage basin)-

Ex 1.) Rocky mtns.- Continental divide

East to AtlanticW to Pacific •Or to the gulf of Mexico

2.) Mississippi river watershed-

(stream capture):

1.) Two river systems

2.) Continual erosion causes

(occurs often!!!!)

Before

Stream Piracy

After

B AB A

River movement as a river cuts deeper into its bed,

•Younger rivers are

•Older rivers are

Meanders-

*As erosion continues a loop forms (2 way path).

In time, sediments fill in and cut off the loop forming an

Erosion (fast side)

Deposition (slow side)

Delta-

•Similarly when swift mountain streams reach level land at the base of the mountain an ALLUVIAL FAN (AF) forms. (AF’s) consist of coarse sediments.

(AF’s) and ‘s are similar: Fan shaped, deposits of sediments by rivers

(AF’s) differ from deltas

1.) AF’s are on

2.) AF’s have larger

3.)AF’s are on more of a

Flooding- during flood stage,

Faster (erosional)

Slower (depositional)

Slower (depositional)

Sediments settle outSediments settle out

Floodplain-

Floodplain Floodplain

Flash Flood- a single rain

*Most rivers flood only with several days of steady rain/fast snow melting

*Because most rivers drain large areas of land, they may flood areas far from the actual source of water

*Dams can cause flooding- manmade or natural (ice,landslide,volcano) when they break the reservoir drains

Flood prevention

1.) Leave

2.) Reforest and replanting

3.) Damming tributaries

4.) Artificial levees (temporary)

5.) Spillways-