Chapter 13

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 1906 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