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Streams. Chapter 12 Water On and Under the Ground Geology Today Barbara W. Murck Brian J. Skinner. “Grand Canyon of the Yellowstone” Thomas Moran, 1872. N. Lindsley-Griffin, 1999. The Water Cycle.

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Streams

Streams

Chapter 12

Water On and

Under the Ground

Geology Today

Barbara W. Murck

Brian J. Skinner

“Grand Canyon of the Yellowstone” Thomas Moran, 1872

N. Lindsley-Griffin, 1999


The water cycle

The 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

N. Lindsley-Griffin, 1999


Water reservoirs

Water 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

N. Lindsley-Griffin, 1999


Water reservoirs1

Water Reservoirs

Fig. 12.3,

p. 332-33

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


Water reservoirs2

Water Reservoirs

The smallest reservoirs are:

Soil moisture

Water in mineral structures

Atmospheric water

Biosphere

Fig. 12.3, p. 332-33

N. Lindsley-Griffin, 1999


Stream landforms

Stream Landforms

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

Fig. 12.5, p. 335

Entrenched meanders - Colorado River

Dead Horse Point, Utah

N. Lindsley-Griffin, 1999


Relationship between mass wasting and streams

Relationship between mass wasting and streams….

Mass wasting provides a steady supply of sediment for streams to transport and deposit


Streams

Alluvium(stream sediment)

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)

N. Lindsley-Griffin, 1999


Stream discharge

Width

Stream Discharge

Depth

Amount of water passing a point on the bank, per unit of time.

Affected by:

WIDTH of channel

DEPTH of channel

VELOCITY of flow

Velocity

Houghton-Mifflin, 1998; N. Lindsley-Griffin, 1999


Stream discharge1

Stream Discharge

Channel dimensions (width, depth) increase downstream

Velocity increases downstream

Discharge increases downstream

Houghton-Mifflin, 1998; N. Lindsley-Griffin, 1999


Stream profile

Stream 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

Houghton-Mifflin, 1998; N. Lindsley-Griffin, 1999


Base level

Base 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


Stream flow

Stream Flow

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

Houghton-Mifflin, 1998; N. Lindsley-Griffin, 1999


Straight stream channels

“Straight” Stream Channels

Stream channels are never perfectly straight.

Deepest water path curves from side to side.

Fig. 12.6 p. 336

N. Lindsley-Griffin, 1999


Meandering stream channels

Meandering Stream Channels

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.

Houghton-Mifflin, 1998; N. Lindsley-Griffin, 1999


Meandering stream channels1

Meandering Stream Channels

Erosion is greatest on outer edges of bends.

On inner edges, water slows down

and deposits sediment.

Fig. 12.6 p. 336

N. Lindsley-Griffin, 1999


Meandering stream channels2

Meandering Stream Channels

Cut Bank

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

Slumping

Bar

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


Meandering stream channels3

Meandering Stream Channels

Meander cutoffs produce oxbow lakes

Houghton-Mifflin, 1998; N. Lindsley-Griffin, 1999


Stream landforms1

Stream Landforms

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 landforms2

Stream Landforms

Floodplain

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).

Point bar

Oxbow lake

Erosional cutbank

Fig. 12.7, p. 337

N. Lindsley-Griffin, 1999


Stream channels

Stream Channels

A stream that is unable to move all the available sediment load deposits the sediment as bars to produce a braided stream.

Fig. 12.6 p. 336

N. Lindsley-Griffin, 1999


Stream deposits

Stream 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. 338

N. Lindsley-Griffin, 1999


Stream deposits1

Stream Deposits

Platte River - a braided stream.

Sandhill Cranes and Whooping Cranes use the Platte River sandbars for safety at night

USGS, , J.R. Griffin,

N. Lindsley-Griffin, 1999

J.R. Griffin & N. Lindsley-Griffin, 1999


Stream deposits2

Stream Deposits

Death Valley, California

Note fault scarp

Fig. 12.10 , p. 339

Alluvial fan - where the gradient of a stream decreases suddenly, it slows down and deposits its sediment load.

N. Lindsley-Griffin, 1999


Stream deposits3

Fig. 12.9, p. 339

Stream 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.

Floodplain

N. Lindsley-Griffin, 1999


Stream deposits4

Stream Deposits

Natural levees form where floodwaters slow down and deposit sediment at the edge of the channel.

Fig. 12.9, p. 339

Natural levees

N. Lindsley-Griffin, 1999


Stream deposits5

Stream Deposits

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 deposits6

Stream 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


Drainage basins

Drainage Basins

Drainage basin - the total area from which water flows into a stream.

Drainage divide - the topographic high that separates adjacent drainage basins.

Fig. 12.13, p. 341

N. Lindsley-Griffin, 1999


Drainage patterns

Drainage Patterns

Dendritic drainage patterns, characterized by tree-like branches, form on rocks that are relatively homogeneous.

Fig. 12.15, p. 343

N. Lindsley-Griffin, 1999


Drainage patterns1

Drainage Patterns

Radial drainage patterns flow outward from a central high point.

Fig. 12.15, p. 343

N. Lindsley-Griffin, 1999


Drainage patterns2

Drainage Patterns

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

Fig. 12.15, p. 343

N. Lindsley-Griffin, 1999


Drainage patterns3

Drainage Patterns

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

Fig. 12.15, p. 343

N. Lindsley-Griffin, 1999


Streams and plate tectonics

Streams and Plate Tectonics

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.

A

B

C

© Houghton Mifflin 1998; N. Lindsley-Griffin, 1999


Streams of north america

Streams of North America

Major drainages of the U.S. and Canada.

Mississippi River system drains the largest part of North America

© Houghton Mifflin 1998.; N. Lindsley-Griffin, 1999


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