Unit 4.5: External forces fluvial

Question 1

what is a drainage basin?

Answer 1

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

Question 2

what characteristics/features does a drainage basin have?

Answer 2

• 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

Question 3

what are drainage divides?

Answer 3

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

Question 4

what are continental divides?

Answer 4

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

Question 5

what are drainage patterns?

Answer 5

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

Question 6

what are some various types of drainage patterns?

Answer 6

• 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.

Question 7

what are stream orders?

Answer 7

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)

Question 8

what is stream permanence?

Answer 8

indicates how permanent a stream is

Question 9

what are the different types of stream permanence?

Answer 9

• 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)

Question 10

what is fluvial erosion?

Answer 10

erosion by running water

Question 11

what influences the rate of erosion for a stream?

Answer 11

• 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

Question 12

what are some different types of erosion?

Answer 12

• 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

Question 13

define “stream load”

Answer 13

material that moves in a stream channel

Question 14

what are the 3 types of stream load?

Answer 14

• 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

Question 15

what are antecedent streams?

Answer 15

cut through bed rock ridges rather than flow around them

Question 16

what are superimposed streams?

Answer 16

cut through resistant layers of rock and form water gaps

Question 17

what is stream sorting?

Answer 17

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

Question 18

what is an alluvial fan?

Answer 18

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

Question 19

Define “stream gradient”

Answer 19

steepness of a stream, more gradient means more steep

Question 20

what is a braided stream?

Answer 20

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

Question 21

what are meandering streams?

Answer 21

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

Question 22

what is aggradation?

Answer 22

build up of sediments in a stream and floodplain.

Question 23

when do meandering streams occur?

Answer 23

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

Question 24

what features are related to a meandering stream?

Answer 24

• 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.

Question 25

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

Answer 25

• 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.