r&b: bedrock rivers

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the five bedrock river characteristics

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1

the five bedrock river characteristics

fixed channel; high transport capacity; low storage; input = output; strong interaction between streams and hillslopes

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2

what does it mean to have low storage for sediment?

implies all sediment inputs are balanced by downstream transportation

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3

hill-slope channel coupling

when sediment falling from a hillside goes directly down into a river

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4

what sets the pace for landscape lowering in areas where landslides are common?

river incision (if river can't incise bed while also carrying deposited material, then valleys will fill and hillsides lower)

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5

bedrock channels

floored by bedrock, lacking alluvial cover; indicative of high transport

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6

where do waterfalls occur?

where cutting-down occurs (typically where two different types of rock that have two different weathering rates meet)

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7

are waterfalls forever?

no (only exist as long as barrier does)

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8

do waterfalls stay in one place?

no, very transient (move backwards relative to flow)

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9

hanging valleys

catalyst for a glacial waterfall; occur when glacier incises into rock that is higher than floor of main valley

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10

three ways a stream erodes its channel

hydraulic action, solution, abrasion

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11

hydraulic action

occurs when pressure and turbulence of water flow physically moves rock grains; can wedge open preexisting fractures; particularly effective at steep gradients

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12

solution

chemical weathering of bedrock (most prevalent in limestone); can produce large amount of mobile sediment; flowing water increases dissolution rate, deepens channel

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13

abrasion

grinding of bed via friction; impacts rock fragments and sediment grains

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14

base level

defined in many ways, but for now: limiting level below which a stream cannot erode

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15

four types of natural dams

landslide sediments, glacial deposits, glacial ice, and lava flows

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16

what do dams result in?

local base levels (lakes and such)

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17

global base level

ocean

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18

what happens in a stream when base level goes down?

erosion

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19

what happens in a stream when base level goes up?

sediment accumulation

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20

steady-state channels

occur when rate of erosion and rate of uplift roughly balance

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21

topography

relief, slope, and drainage basin morphology

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22

mountain range growth

when rates of uplift are greater than rates of erosion; equals increase in slope and relief

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23

mountain range decay

when rates of erosion are greater than rates of uplift; equals decrease in slope and relief

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24

are the mountain range growth/decay states sustainable?

no; will constantly give way to other depending on erosional rates and tectonic activity

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25

five young valley characteristics

V-shape; rapids and waterfalls; no floodplain; drainage divides are broad and flat; valley actively deepening

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26

five younger mature valley characteristics

V-shape; floodplain present; sand and gravel bars; sharp drainage divides; maximum relief is approached/approaching

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27

maximum relief

when valleys stop deepening

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28

three older mature valley characteristics

wider valley bottom; narrow floodplain; rounded divides; diminished relief

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29

two old valley characteristics

peneplain surface (nearly flat), only erosional resistant rocks remain; river meanders across wide, flat floodplain

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30

what four human activities have lead to increased sediment yield?

clearing of forests, cultivation of land, damming of streams, construction of cities, etc

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31

how much sediment reaches the ocean as a result of anthropogenic damming?

has cut amount of sediment reaching the ocean by half

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