Geological and Cultural Significance of Rivers (L18) Flashcards
Why are streams important pathways of water flow?
b/c they connect land areas that receive water as percipitation with the sea
What happens to most “excess surface water” that doesn’t soak into the ground or is evaporated?
runs off the land and is directed down stream channels and ultimately flows toward the sea
What is a stream?
a body of water that carries rock particles and dissolved ions and flows down slope along a clearly defined path
What are the 5 main reasons why streams are important?
- they deliver much of the water from land to sea
- erode lots of sediment particles and transport them to lower elevations
- carry dissolved ions to the sea (making sea salty)
- sculpt Earth’s surface through processses of erosion and deposition
- to humans, important sources of water and transportation routes for trade
3 main things that can happen to water that falls to the ground as percipitation?
- evaporate back into the atmosphere
- soak into the ground
- flow at the surface as runoff
how does runoff move?
moves over the surface in a thin, continuous sheet and eventually becomes confined to tiny channels called rills
What are rills?
tiny channels that are merged into larger, more permanent, stream channels which are tributaries of even larger streams
what causes land to erode?
due to the streams eroding downward in an effort to reach base level (sea level)
why do erosions tend to dominate at the highest elevations above sea-level?
b/c the greater the elevation above sea level, the greater the rate of downcutting through the land
what are the 2 main ways streams carry clastic sedimentary particles?
as bedload, and suspended load
what are bedloads?
large and/or dense particles that remain on the bed of the stream but can be moved by tumbling and saltation
what is suspended load?
small and/or light particles that are suspended in water most of the time
what decreases the downstream in general?
the volume and sediment grain size of both bedload and suspended load
what makes the sea salty?
the stream carrying dissolved ions from the weathering of minerals contained in rocks on land being transported to the sea (sodium)
2 main types of flow occuring in streams?
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
what is a common misconception of streams?
that streams are faster close to their source than far from their source
How do rivers flow at headwaters? and how do bedloads look?
flow down small, shallow channels where turbulent flow is dominant
bedload tend to be coarse, with clasts of pebble size or bigger
how do rivers flow in lowland areas? and how do bedloads look?
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
what happens in river channels bounded by valleys?
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
why do valleys in rivers tend to be deep and v-shaped?
due to rapid downcutting
why do valleys in the lower parts of a stream’s course tend to be broad?
due to little downcutting and greater lateral movement
what part of the river is the fastest flow and why?
path of highest flow velocity actually tends to veer toward the outer bank
why is the highest flow velocity tend to veer toward the outer bank?
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)
how is helical flow (circulating in a corkscrew fashion) created?
through water flowing rapidly downward an outside bank, across the bottom of the channel, and up the inside bank
when do cutoffs occur?
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
what is an oxbow lake?
an arc-shaped lake created when a meander is isolated due to a cutoff
why is the Mississippi so muddy?
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
what do floods do?
they deposit sediments beyond a river’s channel
What are levees?
ridges that are formed when the coarsest sediment is deposited closest to the channel in a flood
what is a deeper significance to “the levee”
emerged as a great influence in rock and roll
what can we thank for the advent of Rock and Roll and modern pop music?
The Mississippi river
