Stream and River Deposits

1. Stream and River Deposits Pg. 11 - 13

2. Deposition • The process by which material is dropped or settles. • Rivers do this with particles they pick up like soil and rock. • Deposition also forms and renews some of the world’s most productive soils.

3. Deposition in Water • Rock and soil deposited by streams is called alluvium. • Alluvium is dropped at places in a river where the speed of the current decreases. • Erosion occurs on the outside bank where the water flows faster. • Then deposition occurs along the inside bank where the water flows slower.

4. River Deposits • Heavy minerals (like gold) are sometimes deposited where the river slows down. • This alluvium is called placer deposits.

5. Designing a Delta • Rivers slow down when they enter a larger body of water, like a lake or ocean. • Here it forms a fan-shaped deposit called a delta. • When a delta forms it extends the coastline. • This occurs where the Mississippi enters the Gulf of Mexico.

6. Deposition on Land • Sometimes a fast-moving mountain stream flows onto a flat plain, the stream slows down. • Alluvium deposits on the flat plain to form alluvial fans. • Alluvial fans only occur on dry land.

7. Sometimes periods of high rainfall will suddenly increase the volume of water in a stream and cause it to overflow. • The land it spills on to is the flood plain. • Each flood adds another layer of alluvium.

8. Fatal Flooding • Flood plains are good for farming because periodic flooding brings new alluvium rich in minerals. • However, flooding can also damage farmland and homes.