Unit 5 Lesson 4

Unit 5, Lesson 4: 

Unit 5, Lesson 4 Running Water

Running Water: 

Running Water Running water is the major cause of erosion Rivers, streams and runoff (water that flows over the Earth’s surface, usually after a rainfall or spring thaw).

Runoff and Erosion: 

Runoff and Erosion The amount of runoff is affected by several factors The amount of rainfall in an area Amount of plant growth in an area The shape of the land Steeper slopes have greater runoff Gentler slopes have less dramatic runoff

Streams and Erosion: 

Streams and Erosion Gullies formed by runoff are actually tiny stream valleys. When runoff from several gullies comes together, a larger stream forms. The soil particles and rock materials carried by a stream are called the stream’s load. Larger and faster streams carry bigger loads. Streams cause erosion by abrasion.

Deposits by Rivers: 

Deposits by Rivers A stream or river carries a large amount of sediments. Where the river or stream slows down, sediments are deposited, usually around a bend or curve. Rivers tend to erode material on the outside of a curve and deposit it on the inside. Several different formations can result: Oxbow lakes Alluvial fans Deltas Flood plains and levees

Oxbow Lakes: 

Oxbow Lakes Sometimes the meanders of a river form large, U-shaped bends. Erosion along such bends can cut these bends off from the river. Deposited sediments dam up the ends of the meander. An oxbow lake is then separated from the rest of the river

Alluvial Fans: 

Alluvial Fans When a river leaves the mountains and runs out onto a plain, its speed decreases. Nearly all the sediments the river is carrying are dropped. The sediments spread out from the river channel in a fanlike shape called an alluvial fan.

Deltas: 

Deltas Large amounts of sediments deposited at the mouth of a large river that flows into a lake or an ocean form a delta. The river’s speed decreases as it runs into the body of standing water The river cannot carry as much material when it is moving slowly, so it deposits much of the sediments.

Flood Plains & Levees: 

Flood Plains & Levees On both sides of an older river or stream, flat areas called flood plains are formed. After heavy rains or spring thaws, the river overflows its banks and covers the flood plain. Sediments deposited on a flood plain are usually of fine particles. Larger particles, which settle first, are deposited along the sides of the river. These larger particles accumulate to form levees.