chapter 6: fluvial landforms drainage systems origin of stream courses drainage patterns stream...
TRANSCRIPT
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Chapter 6: Fluvial Landforms
• Drainage systems • Origin of stream courses• Drainage patterns• Stream capture
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Hypsometric curves and the stabilization of drainage basin form
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• 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
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• 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
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• Drainage systems
• stream ordering
• what’s outlined in red?
•what’s outlined in yellow?
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• Origin of stream courses
Virgin land surface (new landscapes)
• fresh volcanics• newly glaciated• emergent marine areas• recently uplifted terranes
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• 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
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• 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
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Yemen (very dry climate)http://www.cerritos.edu/earth-science/tutor/Fluvial/drainage_patterns1a.htm
New Zealand, Wikepedia
• Drainage patterns
Yangtze River, ChinaNASA photo
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• Drainage patterns
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• Drainage patterns
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• Stream capture
Diversion of a stream’s flow from its original channel to the channel of
a neighboring stream.
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• 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.
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• Stream capture
• this is example of what type of stream capture?
• where might we seethis in Appalachians?
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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.)
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• Stream capture
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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
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• 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.
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• The Cycle of Erosion
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• The Cycle of Erosion
• sequence of forms: 1) youth 2) maturity 3) old age
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• 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
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• 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
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• 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.
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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
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• 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
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• 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
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• 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
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• 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.
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