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

•higher for steeply sloping,low-permeability landscapes,

which promote runoff, gullying,channeling.

• lower for low-relief, highpermeabilty landscapes.

-what about karst?

4th order drainage

basin

drainage texture-Note crenulated contours

• 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 avirgin 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

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

Yemen (very dry climate)http://www.cerritos.edu/earth-science/tutor/Fluvial/drainage_patterns1a.htm

New Zealand, Wikepedia

• Drainage patterns

Yangtze River, ChinaNASA 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 seethis 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

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 constructional deposition of coarse-grained sediments on

land,fanhead trenching,

mudflows

deltas constructional deposition in standing water,

turbidity currents,birdfoot deltas

• Fluvial landforms

• 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.

Stage Landscape Processes

youthful steep hillsides,drainage divides

predominant V-shaped valleys

headward erosion,stream downcutting

mature rounded hills, valley walls predominant

graded streamsbroad floodplains

lateral erosion, streams adjust to

discharge/load

old age “peneplane,”close to base level

very low relief,sluggish stream flow,

poor drainage

• The Cycle of Erosion

• 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

slopeof stream that formed it.

• may slope up-valley• will not have concave-upward profile as a

valleyfloor would.