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

Hypsometric curves and the stabilization of drainage basin form

Hortons’s hierarchy of 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 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

Drainage systems stream ordering what’s outlined in red? 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 rectangular / angular high-angle junctions, high-angle bends in tributaries jointed rocks annular circular patterns breached domes radial consequent streams flowing in all directions from central high area volcanic or intrusive domes

Drainage patterns Yangtze River, China NASA photo Yemen (very dry climate) http://www.cerritos.edu/earth-science/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 meander 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 landforms Landform 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 deposition of coarse-grained sediments on land, fanhead trenching, mudflows deltas deposition in standing water, turbidity currents, birdfoot deltas

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 of recognizable landforms.

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 narrow, V-shaped valleys

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

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.

The Cycle of Erosion Stage Landscape Processes youthful steep hillsides, drainage divides predominant V-shaped valleys headward erosion, stream downcutting mature rounded hills, valley walls predominant graded streams broad floodplains lateral erosion, streams adjust to discharge/load old age “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 filling of valley by aggradation of graded stream

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.