1. Chapter 7: Erosion and Deposition
7.1: Forces wear down and build up Earth’s surface
7.2: Moving water shapes land
7.3: Waves and wind shape land
7.4: Glaciers carve land and move sediments

2. 7.2 Moving water shapes land
Before, you learned:
Erosion is the movement of rock and soil
Gravity causes mass movements of rock and soil
Now, you will learn:
How moving water shapes Earth’s surface
How water moving under ground forms caves and other features

3. Streams shape Earth’s surface
Think about a river:
Surrounding land is higher than the river
Steep valley: see the river is the low point
Even in very flat places, land is sloping down to the river, which is running downhill through the land
Water running downhill changes the land:
Shapes landforms by moving sediment in the processes of erosion and deposition
Water can carve out new features underground

4. Drainage Basins and Divides
Where does water go when it rains or ice melts on a slope?
Soaks in the ground
flows down the slope in thin sheets
Becomes part of a channel that forms a stream
Stream: any body of water that flows down a slope along a channel
Streams flow into one another to form complex drainage systems
Small flow into larger
Drainage Basin: area of land in which water drains into a stream system
Water usually eventually drains into a lake or ocean

5. Drainage Basins and Divides
Drainage basins are separated by ridges called divides
A ridge from which water drains to one side or the other
Can be along a mountain, or simply the highest line of land
Are boarders of drainage basins

6. The Continental Divide
Runs from Alaska to Mexico
Most water that falls west: drains to the Pacific Ocean
Most water that falls east: drains into the Gulf of Mexico or the Atlantic Ocean

7. Valleys and Floodplains
As streams flow and carry away sediment, they form valleys
In high mountains they often cut V-shaped valleys that are narrow and steepwalled
In low areas, they may form broad valleys that include floodplains
An area of land on either side of a stream that is underwater when the stream floods
Can make the land very fertile when it deposits sediments

8. Stream Channels
Meanders: twisting and looping pattern in a stream channel
Erodes the outside banks and deposits sediment along the inside banks
A flood can cause a new channel to form, cutting off the meander into a crescent-shaped lake: oxbow lake

9. Alluvial Fans and Deltas
Streams also create landforms called alluvial fans and deltas, formed by deposition of sediment
Alluvial fan: fan-shaped deposit of sediment at the base of a mountain
Forms where a stream leaves a steep valley and enters a flatter plain
Stream slows down and spreads out, depositing sediment
Delta: area of land formed by the buildup of sediment at the end, or mouth, of a river
When the river enters the ocean, it slows, depositing sediment
Sediment gradually builds up to form a plain

10. Water moving underground forms caverns
Some rainwater runs into surface streams, some evaporates, some is absorbed by plants…and some soaks into the ground and becomes groundwater
Deep below, spaces in soil and rock become completely filled with water
The top of this region is called the “water table”
Below the water table is “groundwater”
Can change with rainfall

11. Groundwater
Can cause erosion deep below where it slowly flows through underground beds of rock and soil
Rainwater is slightly acidic and can dissolve certain rocks, such as limestone
The groundwater can dissolve some of the limestone and carry it away
Can form caves
Large caves = caverns
If the water table drops, the cavern can be filled with air
Cavern System of passageways, containing lakes and streams
Sinkhole: a basin that forms when the roof of a cave becomes so thin that it suddenly falls in
Possibly because water that supported the roof drained away

12. http://www.pbs.org/wnet/nature/lessons/breaking-it-down/video-segments-violent-hawaii/1702/ - hawaii
- bill nye