Chapter 6: Fluvial Landforms

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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
• Hortonss 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, high
• permeabilty landscapes.
• -what about karst?

drainage texture -Note crenulated contours
4th order drainage basin
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• Drainage systems
• stream
• ordering
• whats
• outlined in
• red?
• whats
• 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 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

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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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• Drainage patterns

Yemen (very dry climate) http//www.cerritos.edu/e
arth-science/tutor/ Fluvial/drainage_patterns1a.ht
m
New Zealand, Wikepedia
Yangtze River, China NASA photo
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• Drainage patterns

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• Drainage patterns

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• Stream capture

Diversion of a streams 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 see
• this 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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• 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 constructional deposition of coarse-grained sediments on land, fanhead trenching, mudflows
deltas constructional deposition in standing water, turbidity currents, birdfoot deltas
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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 findwhy?
• uplifted peneplains?erosional surfaces
• complicated by existence of broad, flat surfaces
  not result of fluvial processes.

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• 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
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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
  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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