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 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 Drainage systems stream ordering Drainage density D L A measure of how well or poorly a basin is drained by streams drainage texture Note crenulated contours higher for steeply sloping low permeability landscapes which promote runoff gullying channeling lower for low relief high permeabilty landscapes what about karst 4th order drainage basin Drainage systems stream ordering what s outlined in red what s outlined in yellow Origin of stream courses Virgin land surface new landscapes fresh volcanics newly glaciated emergent marine areas recently uplifted terranes 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 Drainage patterns Pattern Origin Characteristics Geology dendritic insequent random acute angle junctions homogeneous horizontal beds trellis subsequent parallel streams high angle junctions heterogeneous tilted beds rectangula r angular subsequent high angle junctions high angle bends in tributaries jointed rocks annular subsequent circular patterns heterogeneous breached domes radial consequent streams flowing in all directions from central high area volcanic or intrusive domes Drainage patterns Yemen very dry climate http www cerritos edu earthscience tutor Fluvial drainage patterns1a htm New Zealand Wikepedia Yangtze River China NASA photo Drainage patterns Drainage patterns Stream capture Diversion of a stream s flow from its original channel to the channel of a neighboring stream 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 meande bend of another stream Stream capture this is example of what type of stream capture where might we see this in Appalachians The Hadhramawt Plateau of South Yemen exhibits a complex dendritic drainage pattern and excellent examples of stream piracy Wadi Hadhramawt opens into the sand filled Ramlat Sabatayn 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 Stream capture Fluvial Landform landforms Origin Processes Materials floodplains constructional lateral and vertical accretion channel and overbank deposits pediments destructional lateral planation sheet and rill wash weathering formation of graded surface alluvial fans constructional deposition of coarsegrained sediments on land fanhead trenching mudflows deltas constructional deposition in standing water The Cycle of Erosion introduced by Davis 1909 a foundational 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 The Cycle of Erosion The Cycle of Erosion sequence of forms 1 youth 2 maturity 3 old age The Cycle of Erosion Youthful stage initial drainage poorly developed consequent drainage initiated low drainage density swamps and lakes insequent drainage begins to develop headward erosion and vertical downcutting dominant steep stream gradients promote valley deepening 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 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 The Cycle of Erosion Stage Landscape Processes youthful steep hillsides drainage divides predominant V shaped valleys headward erosion stream downcutting mature old age rounded hills valley walls predominant graded streams broad floodplains lateral erosion streams adjust to discharge load peneplane close to base level very low relief sluggish stream flow poor drainage Cyclic stream terraces former valley floors that lie above active stream channels result from uplift change in base level change in load discharge interrupts cycle of erosion 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 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 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