Physical Geography Unit 4
Terms
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- Fluvial
- 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?
- water
- Fluvial processes dominate ___ of the earth's land area.
- 3/4
- 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.
- Erosion
- 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
- Abrasion
- material carred in running water is capable of scraping rocks in the bed and bank of a stream.
- Solution/carbonation
- 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
- discharge
-
-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
- steep
- rivers and streams have ? gradients along their middle reaches
- moderate
- rivers and streams have ? gradients further down stream
- gentle
- 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
- RI=
- (N+1)/Rank
- Transportation
- 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
- load
- 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
- Deposition
- 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
- alluvium
- 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
- badlands
- 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
- meandering
- 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.
- Deltas
- 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
- Plateaus
- are extensive areas of relatively flat land in places of higher elevation
- Mesas
- have steep sides and appear to be somewhat smaller plateaus surrounded by lower lying plains
- Buttes
- are even smaller, flat-topped elevated places with steep sides
- Glaciers
- are masses of freshwater ice, formed on land, and which are in or have been in motion
- The chief source of glacial ice
- snow
- 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
- small
- 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
- Australia
- 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
- 90,000
- 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
- Drift
- the term used to describe all deposits of glacial origin
- Till
- 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