1. Chapter 13
13.3 River Valleys

2. River Valleys
Rain may form a small valley in soft bedrock on hill slope via headwater erosion
Form in wet areas
Stream cuts a gully and may disappear
Each rain increases
Length
Width
Depth of River

3. Headward Erosion
is demonstrated in this photo taken near Mount Tamalpais in Marin County, California. Groundwater sapping is causing this gully to lengthen up the slope.

5. Permanent River Stream cuts down deep enough to become permanent
If tributaries become permanent, then river system is born

6. Canyons and V shaped Valleys
River Valley
Canyon

7. Canyons, Gorges and Chasms
Very Steep almost Vertical sides
Regions of less rainfall
Form 2 ways:
Lack of rainfall
Erosion resistant rocks
Formation Factors:
Type of rock
Amount of water
Sediment in river
Climate of region

8. Gorge

9. Young Valley V-shaped Valleys Young River River cuts down into channel
Upper valley walls widened by erosion

10. Old Valley U-Shaped Valley Less erosion of bed
More erosion of channel sides
Wide valley, broad floor, gently sloping sides

11. Base Level
Stream cannot erode bed lower than body of water it flows into
Sea level is ultimate base level

12. Stream Piracy or stream capture
Headward erosion cuts through divide
One river captures or “pirates” the headwaters of another river
River grows larger
Expands drainage basin
Formation process of great river systems
Mississippi, Nile, Ganges, etc.

13. Rapids
Steep riverbed
Water velocity is fast
Forms white-water rapids

14. Rapids

15. Waterfall Water flows over hard rock Erodes softer rock below
Falls are temporary
Undermines rock above leaving overhang
Overhang breaks off
Waterfall recedes upstream

16. Worlds Best WaterFalls