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Chapter 6: Fluvial Landforms

Chapter 6: Fluvial Landforms. Drainage systems Origin of stream courses Drainage patterns Stream capture. Hypsometric curves and the stabilization of drainage basin form. Drainage systems stream ordering Hortons’s hierarchy of streams lower order streams are:

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Chapter 6: Fluvial Landforms

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  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

  17. Fluvial landforms

  18. 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.

  19. The Cycle of Erosion

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

  21. 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

  22. 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

  23. 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.

  24. The Cycle of Erosion

  25. 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

  26. 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

  27. 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

  28. 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.

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