StreamsStreams
Chapter 12
Water On and
Under the Ground
Geology Today
Barbara W. Murck
Brian J. Skinner
N. Lindsley-Griffin, 1999
“Grand Canyon of the Yellowstone” Thomas Moran, 1872
The Water CycleThe Water Cycle
Earth’s water cycle, the movement of water from one reservoir to another, is driven by solar energy and gravity
N. Lindsley-Griffin, 1999
Fig. 12.1
p. 328
Water ReservoirsWater Reservoirs
Most water is stored in the oceans (>97.5%) - all salty
Only 2.5% is fresh water.
Ice sheets store most of the fresh water - all frozen
N. Lindsley-Griffin, 1999
Fig. 12.3, p. 332
Water ReservoirsWater Reservoirs
Most of the unfrozen fresh water is groundwater, contained in pore spaces beneath Earth’s surface.
Only a tiny fraction is surface water in streams and lakes.
N. Lindsley-Griffin, 1999
Fig. 12.3,
p. 332-33
Water ReservoirsWater Reservoirs
The smallest reservoirs are:
Soil moisture
Water in mineral structures
Atmospheric water
Biosphere
N. Lindsley-Griffin, 1999
Fig. 12.3, p. 332-33
Streams are most important for their ability to shape the landscape by erosion and deposition.
N. Lindsley-Griffin, 1999
Stream Landforms
Stream Landforms
Entrenched meanders - Colorado River
Dead Horse Point, Utah
Fig. 12.5, p. 335
Relationship between mass wasting and streams….
Mass wasting provides a steady supply of sediment for streams to transport and deposit
Where deposited from high-energy streams: subangular to rounded and poorly sorted overall, although individual beds may be well sorted.
Lower-energy streams: moderately to well sorted and rounded; finer grained
Well layered; evidence of currents (crossbeds, troughs,
ripples, graded beds)
Alluvium(stream sediment)
Alluvium(stream sediment)
N. Lindsley-Griffin, 1999
Stream DischargeStream Discharge
Houghton-Mifflin, 1998; N. Lindsley-Griffin, 1999
Amount of water passing a point on the bank, per unit of time.
Affected by:
WIDTH of channel
DEPTH of channel
VELOCITY of flow
Depth
Width
Velocity
Stream DischargeStream Discharge
Houghton-Mifflin, 1998; N. Lindsley-Griffin, 1999
Channel dimensions (width, depth) increase downstream
Velocity increases downstream
Discharge increases downstream
Stream ProfileStream Profile
Houghton-Mifflin, 1998; N. Lindsley-Griffin, 1999
Cross section along a stream’s length:
Concave-up
Varies according
to gradient or
slope steepness
Hudson River -
high gradient
Nile River -
low gradient
Base LevelBase Level
Elevation below which a stream cannot erode its channel
Sea level is ultimate base level
LOCAL BASE LEVELS: Lakes, dams, resistant ledges
Houghton-Mifflin, 1998; N. Lindsley-Griffin, 1999
Maximum velocity - center
Maximum turbulence - edges
Laminar flow: Water moves in straight paths
Turbulent flow: Water moves chaotically, causes suspension of particles and greatest erosion
Stream FlowStream Flow
Houghton-Mifflin, 1998; N. Lindsley-Griffin, 1999
Stream channels are never perfectly straight.
Deepest water path curves from side to side.
N. Lindsley-Griffin, 1999
“Straight” Stream Channels“Straight” Stream Channels
Fig. 12.6 p. 336
As stream flow becomes more turbulent, the current begins to swing back and forth. Where current strikes bank, erosion is enhanced and stream meanders develop.
Meandering Stream ChannelsMeandering Stream Channels
Houghton-Mifflin, 1998; N. Lindsley-Griffin, 1999
Erosion is greatest on outer edges of bends.
On inner edges, water slows down
and deposits sediment.
N. Lindsley-Griffin, 1999
Fig. 12.6 p. 336
Meandering Stream ChannelsMeandering Stream Channels
Beal Slough - entrenched meanders, maximum erosion on outside of bend, deposition on inside of bend.
N.Lindsley-Griffin, W.J.Wayne, 1999
Meandering Stream ChannelsMeandering Stream Channels
Bar
Cut Bank
Slumping
Meander cutoffs produce oxbow lakes
Houghton-Mifflin, 1998; N. Lindsley-Griffin, 1999
Meandering Stream
Channels
Meandering Stream
Channels
Floodplains consist of the relatively flat valley floor that is inundated when the stream overflows its banks.
Houghton-Mifflin, 1998; N. Lindsley-Griffin, 1999
Stream Landforms
Stream Landforms
N. Lindsley-Griffin, 1999
Stream LandformsStream Landforms
Oxbow lake
Erosional cutbank
Point bar
Valley widens by lateral erosion.
Floodplain builds up by deposition
Finest sediment is clay on floodplain or in oxbow lake.
Point bars have coarser sediment (gravel, sand).
Fig. 12.7, p. 337
Floodplain
A stream that is unable to move all the available sediment load deposits the sediment as bars to produce a braided stream.
N. Lindsley-Griffin, 1999
Stream ChannelsStream Channels
Fig. 12.6 p. 336
Stream DepositsStream Deposits
Braided streams have constantly shifting channels and bars, usually of sand and mud.
Braided patterns form where discharge varies greatly and banks supply large amounts of easily eroded sediment.
Bramaputra River
Fig. 12.8, p. 338N. Lindsley-Griffin, 1999
Platte River - a braided stream.
Sandhill Cranes and Whooping Cranes use the Platte River sandbars for safety at night
J.R. Griffin & N. Lindsley-Griffin, 1999USGS, , J.R. Griffin, N. Lindsley-Griffin, 1999
Stream DepositsStream
Deposits
Stream DepositsStream
Deposits
Alluvial fan - where the gradient of a stream decreases suddenly, it slows
down and deposits its sediment load.N. Lindsley-Griffin, 1999
Death Valley, California
Note fault scarp
Fig. 12.10 , p. 339
Stream DepositsStream Deposits
Floodplains form where floodwaters spread out across the valley floor. As water leaves the channel, its capacity to carry sediment decreases sharply. Fine, fertile sediment settles out.
N. Lindsley-Griffin, 1999
Floodplain
Fig. 12.9, p. 339
Stream DepositsStream Deposits
Natural levees form where floodwaters slow down and deposit sediment at the edge of the channel.
Fig. 12.9, p. 339 N. Lindsley-Griffin, 1999
Natural levees
Delta - triangular deposit of sediment
where a stream flows into standing water
(ocean or lake)
Nile River, entering Mediterranean Sea
Fig. 12.11, p. 430
N. Lindsley-Griffin, 1999
Stream DepositsStream Deposits
Over time, deltas build out into the standing body of water.
Fine sediment is carried far out and deposited as “bottomset” beds.
Most sediment is deposited
as “foreset” beds at the
steep delta front, which
advances forward over
the bottomset beds.
“Topset” beds consist of
fine sediment deposited
on the delta surface
during floods.N. Lindsley-Griffin, 1999
Stream DepositsStream
Deposits
Drainage BasinsDrainage Basins
Drainage basin - the total area from which water flows into a stream.
Drainage divide - the topographic high that separates adjacent drainage basins.
N. Lindsley-Griffin, 1999 Fig. 12.13, p. 341
Drainage PatternsDrainage Patterns
Dendritic drainage patterns, characterized by tree-like branches, form on rocks that are relatively homogeneous.
N. Lindsley-Griffin, 1999 Fig. 12.15, p. 343
Drainage PatternsDrainage Patterns
Radial drainage patterns flow outward from a central high point.
N. Lindsley-Griffin, 1999 Fig. 12.15, p. 343
Drainage PatternsDrainage Patterns
Rectangular drainage patterns, characterized by sharp bends, form on jointed rocks.
N. Lindsley-Griffin, 1999 Fig. 12.15, p. 343
Drainage PatternsDrainage Patterns
Deranged drainage patterns are characterized by streams that appear or disappear suddenly, typical of karst regions.
N. Lindsley-Griffin, 1999 Fig. 12.15, p. 343
© Houghton Mifflin 1998; N. Lindsley-Griffin, 1999
A B C
A. 100 m.y. ago, the Amazon River flowed east to west. South America and Africa began to rift apart across Atlantic Ocean.
B. 15 m.y. ago, subduction of the Nazca plate began. The Andes volcanic arc formed along western edge of South America. Amazon River drainage was blocked.
C. Today, Amazon River flows from west to east.
Streams and Plate TectonicsStreams and Plate Tectonics
© Houghton Mifflin 1998.; N. Lindsley-Griffin, 1999
Major drainages of the U.S. and
Canada.
Mississippi River system drains the
largest part of North America
Streams of North
America
Streams of North
America