Chapter 6: Fluvial Landforms

1. Chapter 6: Fluvial Landforms • Drainage systems • Origin of stream courses • Drainage patterns • Stream capture

2. Hypsometric curves and the stabilization of drainage basin form

3. Drainage systems • stream ordering • Hortons’s hierarchy of • streams • lower order streams are: • shorter, • steeper, • drain smaller areas • Drainage density • D = L/A • measure of how well or poorly • a basin is drained by streams 4th order drainage basin

4. Drainage systems • stream ordering • Drainage density • D = L/A • measure of how well or poorly • a basin is drained by streams • higher for steeply sloping, • low-permeability landscapes, • which promote runoff, gullying, • channeling. • lower for low-relief, high • permeabilty landscapes. • -what about karst? drainage texture -Note crenulated contours 4th order drainage basin

5. Drainage systems • stream • ordering • what’s • outlined in • red? • what’s • outlined in • yellow?

6. Origin of stream courses • Virgin land surface (new landscapes) • fresh volcanics • newly glaciated • emergent marine areas • recently uplifted terranes

7. Origin of stream courses • What determines the path taken by a stream on a • virgin land surface (new landscapes)? • slope of ground • consequent streams • random headward erosion • homogeneous materials • insequent streams • selective headward erosion • materials of varying resistance • subsequent streams

8. Drainage patterns

9. Drainage patterns Yemen (very dry climate) http://www.cerritos.edu/earth-science/tutor/ Fluvial/drainage_patterns1a.htm New Zealand, Wikepedia Yangtze River, China NASA photo

10. Drainage patterns

11. Drainage patterns

12. Stream capture Diversion of a stream’s flow from its original channel to the channel of a neighboring stream.

13. Stream capture • Two types: • abstraction– faster rate of headward erosion on one side of drainage • divide because of steeper gradient or less resistant rocks. • intercession – lateral movement of meander bend intersects meander • bend of another stream.

14. Stream capture • this is example of • what type of stream • capture? • where might we see • this in Appalachians?

15. The Hadhramawt Plateau of South Yemen exhibits a complex dendritic drainage pattern and excellent examples of "stream piracy." WadiHadhramawt opens into the sand-filled RamlatSabatayn in the southwest corner of the Rub-al-Khali (The Empty Quarter), yet drainage is toward the sea. The southern coast of the Arabian Peninsula is at the upper portion of the photograph. (S65-34658; Gemini IV.)

16. Stream capture

18. Fluvial landforms

21. The Cycle of Erosion • introduced by Davis (1909), afoundational concept in geomorphology for many years, formed basis for interpreting landforms. • idealized sequence of landscape/landform evolution. • begins with uplifted, virgin landscape. • culminates with featureless plane eroded to base level. • in between passes through stages, each with a set of recognizable landforms.

22. The Cycle of Erosion

23. The Cycle of Erosion • sequence of forms: 1) youth 2) maturity 3) old age

24. The Cycle of Erosion • Youthful stage • initial drainage poorly developed • consequentdrainage initiated • low drainage density • swamps and lakes • insequentdrainage begins to develop • headward erosion and vertical downcuttingdominant • steep stream gradients promote valley deepening • narrow, V-shaped valleys

25. The Cycle of Erosion • Mature stage • reduction in basin relief • streams become graded (adjust to load and discharge) • stream gradients reduced, valley widening accelerates • V-shaped valleys transition to flatter profiles • flood plains develop • valley sides and divides are smoothed and rounded

26. The Cycle of Erosion • Old age – “penelplane” • gently sloping plane, just above base level • very gradual transition between floodplain and valley walls • real examples hard to find—why? • uplifted peneplains?—erosional surfaces • complicated by existence of broad, flat surfaces not result of fluvial processes.

27. The Cycle of Erosion

29. Cyclic stream terraces • former valley floorsthat lie above active stream channels. • result from: • uplift • change in base level • change in load/discharge • interrupts cycle of erosion

30. Types of cyclic stream terraces • cut-in-bedrock terraces • bedrock terraces • covered by thin veneer of alluvium • interpreted events: • erosion by graded stream • uplift/change of base level • downcutting • fill terraces • composed of alluvium, depositional in nature • interpreted events: • filling of valley by aggradation of graded stream • uplift/change of base level • downcutting

31. Types of cyclic stream terraces (cont.) • cut-in-fill terraces • composed of alluvium, erosional in nature • interpreted events: • valley cut into alluvium • uplift/change in base level • downcutting • nested fill terraces • composed of alluvium, • multiple terraces, all depositional in nature • successive cycles of aggradation and downcutting

34. Non-cyclic surfaces • erosional surfaces on resistant materials • do not represent periods of sustained erosion but rather a resistant surface. • slope of surface conforms to bedding, not to slope • of stream that formed it. • may slope up-valley • will not have concave-upward profile as a valley • floor would.