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Physical Geography Unit 4


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Latin meaning-river
Fluvial processes
associated with running water
The different forms of running water from raindrops, to thin sheets, to channels creates...
an assortment of erosional and depositional land forms of different scales and shapes
What is the most prevalent geomorphic agent?
Fluvial processes dominate ___ of the earth's land area.
Although water generally moves much slower than wind, it is more...
dense and therefore has the power to move more material
Water moving as sheet flow on the landscape can also...
remove and transport sediment
What are the 3 phases of single activity?
Erosion, Transportation, and Deposition
Erosion, Transportation, and Deposition are...
natural processes but people can alter their rates with changes in land use.
a process where large rocks and unconsolidated (loose) materials are dislodged or dissolved from a part of the earth's surface
Hydraulic action
water easily sweeps away unconsolidated materials, but only significant floods can budge large boulders
material carred in running water is capable of scraping rocks in the bed and bank of a stream.
the dissolving of rocks
The amount of sediment dislodged and eventually swept into a stream...
is related to several factors
the greater the discharge
the greater the amount of sediment eroded
-the amount of water in a stream passing in a particular point in a given amount of time
-a way of accounting for volume
the greater the sediment load in a stream
the more that stream is able to erode
the greater the velosity of the water in a stream...
the greater it's ability to erode
the greater the friction (caused by surface roughness) in a stream...
the greater the amount of turbulance in the water; and this increases running water's ability to carry solid material
the greater the resistance of rocks...
the harder it is to break them down
the steeper the slope
the easier it is for a given amount of water to erode material
the less amount of land surface cover
the greater the rate of erosion
Variation of these factors can occur over short distances leading to...
significant differences in the rate of erosion along different parts of the same stream.
Most streams simultaneously erode...
vertically and horizontally
Steeper gradients across space lead to more
vertical erosion or down cutting in any given stream
Relatively gentle gradients cause more
horizonal erosion
rivers and streams have ? gradients near their headwaters
rivers and streams have ? gradients along their middle reaches
rivers and streams have ? gradients further down stream
Most streams attempt to cut...
down to base level
base level
concept intended to describe the depth a stream will ultimately cut down to
base level for many streams is...
sea level
Many geomorphologists contend that rivers and streams are in
dynamic equilibrium with their environment
dynamic equilibrium
-an apparent "steady state" relationship with their environment (a condition where they appear not to change) until environmental change occurs (such as climate change or tectonic uplift and so forth)
-THEN the river processes change in reaction to environmental changes
Floods are ? and ? events.
periodic; natural
Floods can occur
-when a river or stream channel recieves more water than it can handle in a certain period of time
-happens 2 out of 3 years in natural streams
People usually attach negative connotations to floods because
we choose to live in flood plains
flood plain
the portion of the stream that usually does not contain water, but which occasionally contains water when the channel exceeds bank full discharge
Floods are important because
they have the large amounts of energy needed to cause rapid erosional changes
Floods occur at varying ? and ?
magnitudes; frequency
Higher magnitude floods
larger discharge, lower frequency
lower magnitude floods
less discharge, higher frequency
Recurrence interval (or return period)
the number of years between floods of equal or greater magnitude
refers to the actual movement of sediment, rocks, or dissolved materials
Once a particle has been eroded..
it takes much less energy to continue moving it
A substantial portion of any stream's ? consists of dissolved material
Suspended sediment
-another large component of a stream's load
-relatively fine textured material mixed in with the water
Bed load
-coarse materials
-they are too heavy to remain suspended
The materials in bed load...
role, bounce, or slide along the stream bottom and usually only when there is relatively high discharge and velocity
coarse materials are called
bed load because they are too heavy to remain suspensed
occurs when a stream's carrying capacity decreases (usually due to reduced volume or velocity)
carrying capacity always changes, and when it declines...
some of the stream's load stops moving
the first materials deposited are the heaviest; then...
progressively smaller materials are deposited until the stream's load is reduced to it's capacity
very fine textured materials may remain
suspended indefinitely
accumulations of stream laid deposits
where are thick deposits of alluvium found?
near stream banks and along valley floors and they can be quite fertile
Where are the stream's carrying capacity more likely to be exceeded?
inside bends of streams; places where the stream channel widens; along the lower reaches of a stream (especialy when it empties into a standing body of water); and behind dams in reservoirs
river systems are separated into ____ or ____
watersheds or drainage basins
small creeks join to form what?
progressively larger steams which join to form still larger streams
It is the entire network of creeks, streams and rivers that
drain all runoff from watersheds
all tributaries meet a master stream, the discharge, width and...
depth of the master stream increase
drainage divides
the boundaries of watersheds
drainage divides are "topographic hights" that mark...
places where water flows down slope in one direction or the other.
Where is the most significant drainage divides?
the continental divide in North America
are large areas of rugged topography created by erosioin and are created when easily eroded materials are washed away in such quantities
badlands can also be called what?
erosional hills or mountains because they are formed when large areas are dissected by running water
rivers are dynamic environments which are
environmental systems are intricately connected to each other so that changes in one system are propagated through many others
Physical processes make
meandering streams the most common form of river channel
is the form that conserves energy and tends at the same time to make energy expenditure along the stream line most uniform
The “loops” in meandering streams may eventually become so large that they
are cut off from the main channel leaving oxbow lakes (which eventually become filled with sediment.)
natural levees
the somewhat more elevated areas of land on either side of a channel banks
When streams overtop their banks
water leaving the channel is quickly exposed to much more friction than in the stream
elevated areas slow the water down and
and forces the heaviest sediments (like sand and course silt) to be deposited on and near the banks creating a natural levee
elevated areas can be as high as
15 feet above the adjacent flood plain along the lower end of the Mississippi River, but in most other (smaller) streams they are usually are much lower
Back swamps
are low lying portions of the flood plain lying between the natural levee and edge of flood plain (bluffs)
the concept of flood plains comes primarily from
the eastern half of the United States where such features are relatively well defined
In many parts of the western U.S., flood plains (in the eastern sense of the term) are
not present
Deeply cut (incised) streams may have no flood plain at all and some braided streams may cover a wide area that might otherwise be called a
flood plain
there is little or no flood plain in relatively young mountain streams presumably because
down cutting is too rapid to allow much if any lateral movement
Outside mountainous regions down cutting is slow enough that
lateral shifting (eroding) makes the valley and flood plain wider than the channel itself
river terrace
is an abandoned flood plain located above the present stream including flood plain
Changing climate or tectonic uplift may cause
down cutting below the existing flood plain, and if enough time passes, a new flood plain is created below the original one
If incision and aggradation [deposition] occur repeatedly, it is possible to develop
any number of terraces
Waterfalls and rapids
are portions of channels with steep gradients. Erosion is most intense here and these features are eventually worn “back.
are deposits of alluvium formed when streams enter standing water (either lakes or oceans). The word comes from the Greek letter delta, which is the shape of the classic Nile River Delta in Egypt
As with natural levees, the sudden reduction of carrying capacity causes the river
to deposit its sediment
Deltas take on a variety of shapes and sizes depending on the
coastline, sediment load, water depth, and off shore currents
These seaward extensions of the flood plain can be
fertile if drained
Alluvial fans are usually found in relatively
dry and mountainous environments
They are much like deltas in that
when the swift moving mountain streams reach the valley, they slow down and deposit much material
Because they form in dry environments, they usually do not have
water in them
are extensive areas of relatively flat land in places of higher elevation
have steep sides and appear to be somewhat smaller plateaus surrounded by lower lying plains
are even smaller, flat-topped elevated places with steep sides
are masses of freshwater ice, formed on land, and which are in or have been in motion
The chief source of glacial ice
Accumulations producing glaciers occur only when
snowfall is greater than melting & sublimation in the zone of accumulation
Glaciers currently cover a relatively _____ portion of the earth’s land area
Alpine glaciers
are more like frozen rivers that exist at very high elevations, sometimes near the equator
Alpine glaciers can reach up to a ____ in width and maybe as much as ____ miles long.
mile; 60
Alpine glaciers exist on all continents except
Continental Glaciers
(frequently called ice sheets) currently cover huge land areas in very high latitudes
96% of the world’s glaciers are in
Antarctica and Greenland
_____% of Greenland and _____% of Antarctica is covered with glacial ice
80%; 90%
glaciers reached as far south (in the U.S.) as
southern Illinois
Deeply buried glacial ice
provides a snapshot of what the atmosphere was like roughly 250,000 years ago
The most recent ice age was not only colder, it was also more
rainy and this created some huge lakes in North America
ages can last approximately ______ years
Glaciers are the most powerful tool
in the erosional arsenal
what is left of Lake Bonneville
Great Salt Lake
Great Salt Lake is more salty than ocean water because
because it has no outlet—so the only way incoming freshwater can be removed is through evaporation—which leaves impurities behind.
deepened pre-existing valleys, which are now
deep lakes (Great Lakes and Finger Lakes)
Isostatic rebound
the term used to describe the long-term rising of portions of the earth’s surface which are literally rebounding to pre-glacier elevations
Solid ice can scrape land like sand paper; but it can also
pluck materials from the ground
The tremendous weight of glaciers creates enough pressure to move large objects that
water can not move.
move material in a forward direction and
drop it off at the leading edge (the zone of ablation) much like a conveyer belt
the term used to describe all deposits of glacial origin
the material deposited directly by ice as it melts. It is an unsorted collection of big rocks, fine sediments—and everything in between
stratified sediments
materials that have been sorted by natural processes

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