Geology 101 Quiz 12 Flashcards by Jennifer Lauriello

? are the primary mechanism by which eroded materials are carried off the continent and out to sea

rivers

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geologists estimate that ? of the continent is eroded and carried off in rivers each year; at this rate, the continents would be flat in ? years

0.03mm; 100 million

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the continents are not flat because processes are at work that

continually lift land masses higher, such as collisions between plates

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streams generally get (smaller/larger) downstream

larger

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streams grow larger due to contributions from

tributaries and base flow

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tributaries

smaller streams that discharge into a larger stream

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base flow

groundwater discharge into the stream

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when a mountain stream flows out into a desert, water is lost by

evaporation and by seepage out to the groundwater

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streams can lose water when flower over a

cave opening

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water (does/does not) travel at the same speed in a stream

does not

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the fastest moving water in a gently flowing stream will be found near the ? and ? of the stream

top and center

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if the stream bends, the momentum of water will carry the faster water (closer to/furthest from) the outer bank

closer to

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natures of flow

laminar vs turbulent

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laminar

smooth flow; flow lines travel parallel to each other

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which type of flow is typical of groundwater flow, and very shallow, very slow moving streams?

laminar

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turbulent

rough, tumbling flow; flow lines cross each other’s path

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which type of flow is typical of nearly all streams, especially in rapids?

turbulent

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erosion is more more rapid when stream flow is ? because

turbulent because the turbulence helps scoop sediment from the sides and bottom to keep particles suspended

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five types of sediment transport

suspended load, bed load, saltation, capacity, competence

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suspended load

sediment held in suspension by turbulent flow

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bed load

sediments traveling along the bottom

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saltation

lifting and settling of larger particles along the bottom

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capacity

total sediment load

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competence

ability of stream to carry particles of a particular size

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a small, clear mountain stream will have a ? competence and ? capacity

high competence/low capacity (fast water can carry large particles but small total sediment load)

a large, muddy stream like the Mississippi River will have a ? competence and ? capacity

low competence/high capacity

bedforms

shaped sediments on stream bottom

bedforms: slow, laminar flow produces

no bedforms

bedforms: slow, turbulent flow produces

ripples

bedforms: fast, turbulent flow produces

dunes (essentially oversized ripples)

bedforms: faster flow produces

dunes with ripples

bedforms: very fast flow produces

no bedforms (strips sediments away)

straight stream

streams formed in steep terrain or structurally controlled

structural control means that the stream follows

fault lines or fracture patterns

are straight streams entirely straight?

meandering stream

forms large, continuously migrating loops

what kind of streams are common in flat terrain?

meandering

classic example of a meandering stream

Mississippi River

braided stream

stream divides into multiple channels and rejoins

what kind of streams are common in regions with flat areas and large variations in stream flow?

braided

antecedent stream

a stream that cuts through a mountain range or ridge

if a stream is present before uplift starts, and the stream erodes faster than uplift occurs, then the stream will

continue to flow and keep its channel open as the ridge grows around it

if uplift is faster than stream erosion, the stream will

be forced to go around the rising ridge

essentially, if the stream predates uplift, it will ?; and if the stream is formed after uplift, it will ?

cut through; go around

lateral migration: streams migrate laterally because

they tend to erode on the outside of a bend, where the water moves faster, and deposit sediment on the inside of the bend where the water slows down

oxbow lake

abandoned meander loop

vertical migration: stream channels can migrate both

up and down

? provide a good example of both downward and upward migration of a stream channel

mountains in arid climates

erosion on the mountain side results in a

downward migration of the river

the build up of sediment at the base of the mountains is called an

alluvial fan

floodplain

flat region next to a stream created by flood deposits

why is everything coated with mud after a flood?

the water spilling over the banks spreads out and slows down, so sediment settles out

the size of a floodplain is determined by

the size of the stream and the terrain

a steep sided canyon contains flood waters and results in a ? floodplain

narrow

in areas with ? (not much change in elevation), floodwaters from a large river can spread for miles

low relief

levees

ridge running parallel to stream on either side

levees form during

flooding

terraced floodplains

multiple floodplains at different elevations

terraced floodplains are evidence of

sporadic uplift

when uplift occurs, a stream becomes steeper, and thus faster; faster moving water erodes the underlying rock or sediment and the stream downcuts; floodwater cannot spread as far, and a ? floodplain results

narrower

flood frequency

how often floods of different magnitudes occur

recurrence interval

the average number of years between events of a specific magnitude (the height reached by flood waters)

probability

the chance that a flood of certain magnitude will occur in a given year

probability equation for flooding

P = 100% / Recurrence Interval

the probability that a 50 year flood will occur this year is

100% / 50 = 2%

delta

outward growth of land where a stream discharges into quiet waters of a lake or sea

when a stream reaches the delta, it will often diverse into several smaller streams flowing out into open water; these smaller streams are called

distributaries because they distribute the water

? along the Mississippi River have prevented floods and allowed land to be put to agricultural, industrial, and domestic use in areas that used to be flooded

the levees

subsidence: under normal conditions, periodic flooding deposits sediments on the floodplain; the added weight of the sediment causes the crust to sink down into the mantle, but new sediment ?

counteracts the elevation loss to keep gaining ground

increased risk of catastrophic flooding: any flood that breaches the levee will ?

suddenly change the course of the river, taking it on a much shorter and more direct route to the Gulf

where is the increased flooding concern?

the higher the levees, the more water being held in the river at flood stage, so any flood that successfully breaches these levees will release an immense volume of water with devastating force