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20 Cards in this Set
- Front
- Back
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What are the 3 basic types of rivers/streams?
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braided (high flow), meandering (low flow), distributary (muddy system)
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What are the 5 facies or depositional environments of meandering streams?
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point bars, floodplains, crevasse splays, abandoned channels, levees
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What is a point bar?
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A point bar is a depositional feature of streams.They are crescent-shaped and located on the inside of a stream bend. Point bars are composed of sediment that is well sorted and typically reflects the overall capacity of the stream.
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How are lateral accretion and point bar related?
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lateral accretion is the process by which sediment is building up the poin bar, which is a general fining upward to the top of the bar.
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What is a floodplain?
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Floodplains are strips of land adjacent to rivers that are commonly inundated during seasonal floods. They can be present among braided & meandering rivers.
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What is a crevasse splay?
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Crevasse splays are breaches in natural levees due to rising flood waters.
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What are natural levees?
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They are deposits that are formed primarily on the concave or steep-bank side of meander loops immediately adjacent to the the channel as a result of sudden loss of competence.
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What evidence remains indicating an abandoned channel?
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An oxbow lake
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What is the textural trend of meandering rivers?
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Meandering rivers have a fining-upward trend.
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What type of load do meandering rivers carry?
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meandering rivers carry a mixed load, half suspended and half bed load
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What are the 4 facies of distributary channels?
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straight channels, levees, floodplains, crevasse splays
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What causes distributary channels to develop high levees and to be straight?
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Flowing over mud that is water saturated builds up the levees higher and higher, which also contributes to the streams being straight. this is known as vertical accretion due to subsidence. soft sediment deformationis also common here.
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What is the textural trend of distributary channels?
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There is no textural change
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What kind of load do distributary channels carry?
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distributary channels carry suspended loads
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What are the 3 depositional features/facies of braided rivers?
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transverse bars, longitudinal bars, very little levee or floodplain
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What is a transverse bar?
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A transverse bar is a slightly submerged sand bar extending perpendicular to the shoreline that is found in braided streams.
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What kind of gradient and load do braided streams have?
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braided streams have a high gradient and high bed load. They are also shallow and wide, with typically no levees and uniform texture.
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What kind of sed rocks are typically found in braided streams?
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conglomeratic, coarse, arkosic
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What kind of cross-bedding is associated with braided streams?
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tabular cross bedding
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What kind of cross-bedding is associated with braided streams?
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tabular cross bedding
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