Unit 4.5: External forces fluvial Flashcards Preview

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Flashcards in Unit 4.5: External forces fluvial Deck (25)
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1
Q

what is a drainage basin?

A

an area of land that is drained by a single stream and its tributaries.

2
Q

what characteristics/features does a drainage basin have?

A
  • trunk stream: single large stream into which smaller streams merge
  • tributary: stream that joins with other streams to form a single stream
  • mouth: end of stream where it meets a larger body of water
3
Q

what are drainage divides?

A

drainage basins are separated by these ridges or highlands but the water ends up in the same place

4
Q

what are continental divides?

A

ridges or highlands that separate drainage systems that empty into different ocean basins

5
Q

what are drainage patterns?

A

arrangements of channels in an area; determined by regional steepness, rock resistance, climate, and hydrology

6
Q

what are some various types of drainage patterns?

A
  • dendritic: they’re little tributaries that look like tree branches and slope gently in the direction of the stream
  • deranged: no clear geometry; develops in areas having disrupted surface patterns. its almost like different lakes that are all connected.
  • radical: drainage of a conical mountain flowing in all directions
  • rectangular: right-angle contacts between streams and tributaries. formed by faulted and jointed landscapes
  • trellis: streams flow in only two orientations; developed on parallel folded or dipping rocks
  • centripetal: centric pattern, stream segments drain the interior of an excavated dome.
7
Q

what are stream orders?

A

the ranking of streams in a drainage basin based on signs.

  • 1st order: smallest streams with no tributaries
  • 2nd order: when two or more streams join (has tributaries)
8
Q

what is stream permanence?

A

indicates how permanent a stream is

9
Q

what are the different types of stream permanence?

A
  • intermittent stream: run dry for part/most of the year
  • ephemeral stream: flows briefly only after heavy rain
  • permanent stream: flows year round
  • exotic stream: permanent stream that originates in humid region and flows through arid regions (like the nil)
10
Q

what is fluvial erosion?

A

erosion by running water

11
Q

what influences the rate of erosion for a stream?

A
  • lithology: rock type underlying the stream
  • stream discharge: the faster stream = more erosion
  • location of stream: steep gradient, small channel, greater erosion means more erosion
12
Q

what are some different types of erosion?

A
  • Abrasion: mechanical action; the movement of one material wears away at another material
  • Hydraulic action: water dislodges and drags away rock material from bed and bank. like plucking
  • solution: dissolving of rock material by water
13
Q

define “stream load”

A

material that moves in a stream channel

14
Q

what are the 3 types of stream load?

A
  • dissolved load: material that is invisible dissolved particles. its main contributor is chemical weathering.
  • Suspended load: fine sediment, largest type of stream load. turbulence is key to holding it in suspension.
  • bed load: material that is bounded (saltation) or rolled (traction) along stream bed; heavier particles
15
Q

what are antecedent streams?

A

cut through bed rock ridges rather than flow around them

16
Q

what are superimposed streams?

A

cut through resistant layers of rock and form water gaps

17
Q

what is stream sorting?

A

as velocity decreases, sediment will be deposited and sorted by size. heaviest would drop first

18
Q

what is an alluvial fan?

A

created by stream sorting gently sloping accumulation of sediment deposited at the base of a mountain or arid environment.

19
Q

Define “stream gradient”

A

steepness of a stream, more gradient means more steep

20
Q

what is a braided stream?

A

channel breaks into many tributaries that diverge around sand and gravel bars and then converge again.

21
Q

what are meandering streams?

A

channels that are sinus in form and weave across landscapes. sinuosity is the ratio of actual distance to straight line distance.

22
Q

what is aggradation?

A

build up of sediments in a stream and floodplain.

23
Q

when do meandering streams occur?

A

when suspended load is greater than bed load and presence of random obstacles cause sinuosity.

24
Q

what features are related to a meandering stream?

A
  • Thalweg: fastest flowing water in the stream. this is what erodes the bank to form the bend.
  • point bar: the opposite side that does not get eroded, water is slower
  • cutback: the part that gets eroded and forms the meander.
  • meander neck: distance between bends in meanders that are next to each other
  • oxbow lake: an isolated meander fromed where there is a cutoff; may fill with sediment over time.
25
Q

what are other features that are common in fluvial dispositional environments?

A
  • floodplain: flat, low-lying ground on either side of the stream channel
  • yahoo stream: tributary that is prevented from joining the main stream; flows parallel to main stream
  • wetlands: permanently flooded area
  • natural levees: broad ridges that run along both sides off the channel. built up by recurrent floods (made by alluvium)
  • delta: fan shaped accumulation of sediment that forms where a stream meets with a larger body of water. when the water from the stream enters the larger body, the velocity reduces and the sediment is immediately deposited.