streams chapter 12 water on and under the ground geology today barbara w. murck brian j. skinner n....

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


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


Fig. 12.3, p. 332


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.


Fig. 12.3,

p. 332-33


The smallest reservoirs are:

Soil moisture

Water in mineral structures

Atmospheric water

Biosphere


Fig. 12.3, p. 332-33

Streams are most important for their ability to shape the landscape by erosion and deposition.


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)


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


Channel dimensions (width, depth) increase downstream

Velocity increases downstream

Discharge increases downstream

Stream ProfileStream Profile


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


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


Stream channels are never perfectly straight.

Deepest water path curves from side to side.


“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


Erosion is greatest on outer edges of bends.

On inner edges, water slows down

and deposits sediment.


Fig. 12.6 p. 336


Beal Slough - entrenched meanders, maximum erosion on outside of bend, deposition on inside of bend.

N.Lindsley-Griffin, W.J.Wayne, 1999


Bar

Cut Bank

Slumping

Meander cutoffs produce oxbow lakes


Meandering Stream

Channels

Meandering Stream

Channels

Floodplains consist of the relatively flat valley floor that is inundated when the stream overflows its banks.


Stream Landforms

Stream Landforms


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.


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


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


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.


Floodplain

Fig. 12.9, p. 339


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



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


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.



Radial drainage patterns flow outward from a central high point.



Rectangular drainage patterns, characterized by sharp bends, form on jointed rocks.



Deranged drainage patterns are characterized by streams that appear or disappear suddenly, typical of karst regions.


© 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

streams chapter 12 water on and under the ground geology today barbara w. murck brian j. skinner n....

Documents

water reservoirs

movement of water

downstream slide

deposit slide

water cycle earths water

unfrozen fresh water

stream meanders

soil moisture water