Chapter 16 Flashcards Preview

Geol 101 Lecture > Chapter 16 > Flashcards

Flashcards in Chapter 16 Deck (60):
1

hydrologic cycle

movement of water through Earth's four spheres

2

inflitration

precipitation soaks into the ground

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runoff

precipitation runs over the surface

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transpiration

water absorbed by plants and later transferred to the atmosphere

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evapotranspiration

as evaporation and transpiration both move water from the surface to the atmosphere

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Runoff starts as

sheet flow which develops into tiny channels called rills which forms gullies which form streams

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streams

any water that flows in a channel, regardless of size

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river

carries a substantial amount of water and has many tributaries

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Drainage Basin

stream drains an area of land

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Divide

the imaginary line separating one basin from another; sometimes visible as high ridge mountain region

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3 zones of river systems

Sediment production, sediment transportation, sediment deposition

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Sediment production

zone of a river where more sediment is derived
Located in the headwater region of a river system
Generated by: broken bedrock, bank erosion

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Sediment transport

transported in trunk streams; amount of sediment being eroded equals amount being deposited

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Sediment deposition

when a river reaches a large body of water, the energy decreases and river deposits sediments; usually only fine sediments are deposited in oceans

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laminar flow

water flowing in a nearly straight path

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turbulent flow

water moving quickly in an erratic fashion

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Factors affecting flow velocity

the slope, channel shape, roughness, discharge,

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The slope, or gradient of a stream

steeper gradient has more gravitational energy to drive channel flow

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Channel shape

most effective channel has a small wetted perimeter (area where the rive is in contact with the channel) compared to its cross-sectional area

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Channel size and roughness

increase in channel size will increase the cross-sectional area to wetted perimeter ration thus increasing efficiency; rough channels create turbulence and decreased velocity

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Discharge

volume of water flowing past a certain point in a given unit of time
when discharge increases; the width, depth, flow, and velocity increase

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longitudinal profile

cross-sectional view of a stream
most have a concave shape

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head or headwater

source of the stream

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mouth

the downstream point where the stream empties into a larger body of water
discharge, channel size, and velocity increases towards the mouth

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Quarrying

involves removing large blocks from the channel bed

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abrasion

scraping, bumping, and rubbing
erodes and polishes sediment s

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Potholes

when fast moving, swirling sediment in eddies abrades a hole

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Corrosion

rocks gradually dissolving in flowing water can occur in limestone bedrock channels

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Transport of sediment by streams

Dissolved load (in solution)
Suspended load (in suspension)
Bed load (rolling along the bottom)

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Dissolved load

most of the dissolved load is brought to a stream via groundwater
NOT affect by stream velocity

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Suspended load

largest part of a stream is carried in suspension
amount carried is controlled by stream velocity and settling velocity (speed at which a particle falls through a liquid) of sediments

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Bed load

Coarse sands, gravel, and boulders move along the stream bed by saltation (skipping or jumping)
Less rapid and more localized than transport via suspended load

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Capacity

maximum load of solid particles a stream can carry
The greater the discharge the greater the capacity

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Competence

the maximum particle size a stream can transport
Streams with a faster velocity have a higher competence

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deposition of sediments by a stream

occurs when a stream's velocity is less than the settling velocity

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sorting

particles of the same size are deposited at the same time in this process
Larger particles are settled out first

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alluvium

sediments deposited by streams

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Bedrock Channels

cut into the underlying strata

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meanders

streams transport suspended sediment in broad sweeping bends

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Cutbank

outside of a meander
zone of active erosion

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point bar

inside of a meander
zone of deposition

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cutoff oxbow lake

a meander that has been cut off from joined bends

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braided channel

is a network of converging and diverging channels that thread among numerous islands or gravel bars

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stream valley

channel and surrounding terrain that directs water to the stream
alluvial channels have wide valley floors
bedrock channels have V-shapped valleys

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base level

lowest point to which a stream can erode

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Ultimate base level

sea level

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Local or temporary base level

includes lakes, resistant layers of rock, and large rivers

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changing conditions causes readjustment of stream activities

raising base level= deposition
lowering base level= erosion

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graded stream

only transports sediment

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Deltas

when sediment-filled streams enter a large body of water

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water gap

notch where a river cuts through a ridge that lies in its path

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Antecedent stream

stream existed before the ridge was formed

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Superposed stream

Stream eroded into a preexisting structure

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headward erosion

stream that lengthen its coarse by extending the head of the valley upslope ; can result in stream piracy where the diversion of the drainage of one stream into another

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flood

occurs when the stream exceeds the capacity of its channel; most common and most destructive geological hazard

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Regional flood

seasonal flood that typically result from spring rains or rapid melting of snow

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Flash floods

occur with little or no warning in mountainous areas

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Ice-jam floods

ice forms in rivers creating dams that will break when temperatures rise

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Dam-Failure floods

Dams fail and release large amounts of water

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Flood Control

Artificial levees
Channelization
flood control dams
non-structural approach