Geological and Cultural Significance of Rivers (L18)

Question 1

Why are streams important pathways of water flow?

Answer 1

b/c they connect land areas that receive water as percipitation with the sea

Question 2

What happens to most “excess surface water” that doesn’t soak into the ground or is evaporated?

Answer 2

runs off the land and is directed down stream channels and ultimately flows toward the sea

Question 3

What is a stream?

Answer 3

a body of water that carries rock particles and dissolved ions and flows down slope along a clearly defined path

Question 4

What are the 5 main reasons why streams are important?

Answer 4

1. they deliver much of the water from land to sea
2. erode lots of sediment particles and transport them to lower elevations
3. carry dissolved ions to the sea (making sea salty)
4. sculpt Earth’s surface through processses of erosion and deposition
5. to humans, important sources of water and transportation routes for trade

Question 5

3 main things that can happen to water that falls to the ground as percipitation?

Answer 5

1. evaporate back into the atmosphere
2. soak into the ground
3. flow at the surface as runoff

Question 6

how does runoff move?

Answer 6

moves over the surface in a thin, continuous sheet and eventually becomes confined to tiny channels called rills

Question 7

What are rills?

Answer 7

tiny channels that are merged into larger, more permanent, stream channels which are tributaries of even larger streams

Question 8

what causes land to erode?

Answer 8

due to the streams eroding downward in an effort to reach base level (sea level)

Question 9

why do erosions tend to dominate at the highest elevations above sea-level?

Answer 9

b/c the greater the elevation above sea level, the greater the rate of downcutting through the land

Question 10

what are the 2 main ways streams carry clastic sedimentary particles?

Answer 10

as bedload, and suspended load

Question 11

what are bedloads?

Answer 11

large and/or dense particles that remain on the bed of the stream but can be moved by tumbling and saltation

Question 12

what is suspended load?

Answer 12

small and/or light particles that are suspended in water most of the time

Question 13

what decreases the downstream in general?

Answer 13

the volume and sediment grain size of both bedload and suspended load

Question 14

what makes the sea salty?

Answer 14

the stream carrying dissolved ions from the weathering of minerals contained in rocks on land being transported to the sea (sodium)

Question 15

2 main types of flow occuring in streams?

Answer 15

turbulent (non-linear) flow - dominates near the bottom and sides of a stream channel where swirls are generated around elements of surface roughness

laminar (linear) flow - dominates water that is out of reach of the turbulance and dominate well above the stream bed

Question 16

what is a common misconception of streams?

Answer 16

that streams are faster close to their source than far from their source

Question 17

How do rivers flow at headwaters? and how do bedloads look?

Answer 17

flow down small, shallow channels where turbulent flow is dominant

bedload tend to be coarse, with clasts of pebble size or bigger

Question 18

how do rivers flow in lowland areas? and how do bedloads look?

Answer 18

rivers have larger, deeper, and wider channels with no evidence of turbulence

bedload tend to be finer as clay and silt particles tend to be the only particles that haven’t already settled out

Question 19

what happens in river channels bounded by valleys?

Answer 19

valleys due to streams have their banks destabalized and undercut

these materials then fall down into the stream channel, providing sediment particles for the stream to transport as load

Question 20

why do valleys in rivers tend to be deep and v-shaped?

Answer 20

due to rapid downcutting

Question 21

why do valleys in the lower parts of a stream’s course tend to be broad?

Answer 21

due to little downcutting and greater lateral movement

Question 22

what part of the river is the fastest flow and why?

Answer 22

path of highest flow velocity actually tends to veer toward the outer bank

Question 23

why is the highest flow velocity tend to veer toward the outer bank?

Answer 23

by this happening, the water is pushed up against the bank, elevating water level slight and creating an area of high water pressure at the outer bend (like a water slide)

Question 24

how is helical flow (circulating in a corkscrew fashion) created?

Answer 24

through water flowing rapidly downward an outside bank, across the bottom of the channel, and up the inside bank

Question 25

when do cutoffs occur?

Answer 25

cutoffs occur when the neck of a meander becomes so exaggerated that its easier for the river to cut through the neck than to continue flowing around the meander

Question 26

what is an oxbow lake?

Answer 26

an arc-shaped lake created when a meander is isolated due to a cutoff

Question 27

why is the Mississippi so muddy?

Answer 27

because of the huge amount of suspended sediment carried by the Mississippi to the Gulf of Mexico to ultimately be dumped on the Mississippi Delta at the river’s mouth

Question 28

what do floods do?

Answer 28

they deposit sediments beyond a river’s channel

Question 29

What are levees?

Answer 29

ridges that are formed when the coarsest sediment is deposited closest to the channel in a flood

Question 30

what is a deeper significance to “the levee”

Answer 30

emerged as a great influence in rock and roll

Question 31

what can we thank for the advent of Rock and Roll and modern pop music?

Answer 31

The Mississippi river