Rivers Flashcards
What is the rivers course?
the path of a river as it flows downhill
What are the three courses of a river?
upper, middle, lower
what do rivers form as they flow downhill?
channels and valleys
What does the long profile of a river tell you?
how the gradient changes over different courses
What does the cross profile of a river show you?
what a cross section of the river would look like
Describe the upper course of a river?
- steep
- v-shaped valley
- steep sides
- narrow, shallow channel
Describe the middle course of a river?
- medium gradiant
- gently sloping valley sides
- wider deeper channel
Describe the lower course of a river?
- gentle gradient
- very wide
- very flat valley
- very wide, deep channel
what can erosion be? two things
lateral or vertical
What is vertical erosion?
- deepens river valley making it v-shaped
- dominant in upper course of river
- high turbulence causes rough rocks to be scraped along river bed causing intense downward erosion
What is lateral erosion?
- widens river valley during formation of meanders
- dominant in middle and lower courses
What are the 4 processes of a river?
hydraulic action, abrasion, attrition, solution
What is hydraulic action?
the force the water breaks rock particles away from the river channel
What is abrasion?
eroded rocks picked up by the river scrape and rub against the channel causing it to wear away
What is attrition?
eroded rocks picked up by the river smash into each other and break into smaller fragments . their edges become rounded as they rub together
What is solution?
river water dissolves some type of rock
What are the 4 processes of transportation?
traction, saltation, suspension and solution
What is traction?
large particles like boulders are pushed along the river bed by the force of water
What is suspension?
small particles like silt and call are carried along the water
What is saltation?
pebble sized materials are bounced along the river bed by the force of water
What is solution?
soluble materials dissolve in the water and are carried along
What is deposition?
when a river drops the eroded material its transporting
where are waterfalls and gorges found?
in the upper course of the river
Explain how a waterfall is formed?
- river flows over area of hard rock and then soft rock
- the soft rock is eroded more then hard rock creating a step in the river
- as water goes over step it erodes more and more of softer rock
- steep drop eventually created and waterfall formed
- hard rock eventually undercut by erosion, becomes unstable and collapses
- collapsed rocks are swirled around at foot of waterfall where they erode soft rock by abrasion making a plunge pool
- over time more undercutting and collapsing occurs
- waterfall retreats leaving a steep gorge