topic 4 river processes and pressures Flashcards
What is traction?
Movement of larger rocks rolling along the river bed.
What is saltation?
Hopping motion of particles to heavy to be suspended.
What is solution?
Particles dissolves in water
What is suspension?
Particles carried within water
(Physical)freeze thaw:
Fluctuating tempratures-water expands when frozen.
(Chemical)-acid rain
High pH(acidic) water touches rock
What is a confuence?
Where 2 rivers meet
What is the river land form found in the upper couse?
Waterfalls(gorges
And interlocking spurs
What river land form is found in the middle course?
Meanders and Ox-Bow-Lakes
Discharge
The volume of water flowing in a river at one particular point and time
Measured in cubic meters/second
What is long profile?
The long profile shows how a river’s gradient changes as it flows from its source to its mouth
What is the long profile of a river?
Shows the steepness of a river changes over the course of a river.
The gradient ________ (the slope becomes more gentle)
as the river moves from its upper course towards its lower course.
Decreases
What are the sections of a river’s course?
- upper course
- middle course
- lower course
Whaere in the river is the gradient steepest?
Upper course
What is the cross-profile of a river?
It shows you the cross section of the river
(you can see the shape of the river bed.)
(As rivers flow downhill, they form valleys and channels. The shape of these features changes along the course of the river.)
Corss profile Upper course landmarks:
Erosion>deposition
This means there is the valley is a steep sided( v shaped valley)
-the channel the water flows through is shallow and not very deep.
Corss profile middle course landmarks:
the middle course, neither erosion nor deposition is particularly dominant.
This means that
- the valley has a gentle slope
- the channel is wider and deeper than the upper course
Cross profile-lower course landmarks:
Deposition>erosion
This menas that
- The valley is wide and flat
- The channel is wide and deep
A river’s long profile shows how the _______ changes over its course.
Steepness
What are the characteristics of valleys and channels in the upper courses of rivers?
- shallow channel
- steep valley
- v-shaped valley
- narrow channel
Lateral erosion dominates in the ______course and ______course.
- lower
- middle
Vertical erosion dominates the ______course
Upper
Why is vertical erosion dominant in the upper course?
because high levels of turbulence make rough and angular particles drag along the river bed.
What affects the river’s cross profile?
- vertical erosion
- lateral erosion
How do the processes of erosion work in rivers?
Solution
Solution is where soluble rocks are dissolved by the water in the river or sea (limestone and chalk in particular). They are carried along with the river or sea.
How do the processes of erosion work in rivers?
Attrition
Attrition is where pieces of bedload (material carried by a river or seawater)
are hit against one another.
This causes them to break apart and become smaller and more rounded.
How do the processes of erosion work in rivers?
Hyraulic action:
When the force of water hits against the sea bed or river banks causing rock to break of
How do the processes of erosion work in rivers?
Abrasion:
Where peices of rocks are picked up by the river and hit against the banks, this wears them away.
Which method of transporting sediment involves the sediment dissolving in water?
Solition
Saltation is where small sand and gravel _______ bounce along the river bed or ______bed.
- particles
- sea
What is deposition?
when the sediment that a river is transporting is dropped
This happens in the lower and middle course and in low energy conditions
What are the reasons a river loses velocity and drops material (deposition)
- reduced volume of water in the channel
- increased amount of sediment in the channel
- water becomes shallower
- the river’s mouth is reached
Why does deposition of sediment happen?
A river slows down
What are the 4 processes of erosion?
- abrasion
- attrition
- solution
- hydraulic action
_______ is when the sediment that a river is transporting is dropped.
Deposition
What are the four processes of transportation?
- suspension
- traction
- solution
- saltation
When are gorges formed?
When waterfalls retreat over time
How can a waterfall form?
When a river flows over hard rock that overlays softer rock
Simple explination:(When there is hard rock and soft rock right after, the soft rock gets eroded and it forms a waterfall)
Stage 1 of a waterfall:
The less resistant (softer) rock begins to erode because of ____ and ____.
A step or ____forms in the softer rock, creating a river ____
- Abrasion
- hydraulic action
- notch
- rapid
What is a river rapid?
Rapids are areas along a river where the water flows faster and more turbulent.
Stage 2 of a waterfall:
Over time, the softer rock gets more eroded.
This leaves the hard rock sticking out above the soft rock.
The height of the drop ________ as the water pounds the less resistant rock at the base.
Eventually a waterfall forms.
-increases
What forms at the base of a waterfall over time?
A plunge pool
Stage 3 ofnthe formation of a waterfall:
The less resistant rock starts to be eroded underneath the hard rock.
This process is called_________.
The _________ harder rock collapses because there is nothing underneath it to support it.
The hard rock crumbles into the base and the abrasion between the hard rock and soft rock base creates a __________
Hydraulic action keeps undercutting behind the waterfall.
If the process repeats over a long time, a _____may form.
- Undercutting
- overhanging
- Plunge ppol
- Gorge
Why do interlocking spurs form?
- In the upper course, valleys are steep and V-shaped because most erosion happens vertically
- the rivers do not have a lot of energy because there is not a lot of fast miving water.
This lack of energy means they do not erode latterally, instead they followma winding path because they go around resistant rock
Hillsides on either side of a river that interlock are called interlocking______
Spurs
Name 3 examples of waterfalls:
Niagra falls
Angel falls
Iguazu falls
What erosional process is predominantly responsible for the formation of plunge pools?
Abrasion
Name two Characteristics of valleys in the upper courses of rivers:
- v-shaped
- steep
What are formed when waterfalls retreat over time?
Gorges
What creates a meander?
When a river bends, the current is fastest (carrying the most energy) at the outside of the bend. This high energy water erodes the side of the river, creating a river cliff.
The current is weakest where the water is shallowest, opposite the river cliff. More sediment is deposited here because the current has less energy to carry it along the river. This creates slip-off slopes.
More erosion happens on the _______of river bends, leading to the formation of a _______
- Outside
2. River cliff
Why is more sediment deposited at slip-off slopes than river cliffs?
The water is shallower and the current has less energy
What happens at slip of slopes?
current is weakest where the water is shallowest,
More sediment is deposited here because the current has less energy to carry it along the river. This creates slip-off slopes.
Over time, meanders get bigger until eventually an ox-bow lake forms.
As erosion continues, the river’s bends get nearer to each other and create a ______ neck meander (a small piece of land between bends).
During a flood, high energy water will breach the meander neck.
This makes the river flow in a straighter and faster course.
Over time, deposits will fill in the meander bends.
The meander becomes cut off from the river, forming an ox-bow lake.
Swan’s
What do we call a meander that only has a small bit of land between the bends?
Swan’s neck meander
What is created opposite a river cliff in shallow waters because of deposition?
A slip-off slope
What two processes lead to the formation of meanders?
- erosion
- deposition
What are floodplains?
the wide area of flat land that surrounds rivers in their lower courses at the bottom of a valley. As the name suggests, these areas can flood.
What are floodplains created by?
Meander migration close to the river mouth
They makes valley’s flatter by migrating downstream
What happens to flood plains during floods?
the water loses speed and deposits the sediment that it’s transporting.
This increases the height of the flood plain.
Deposition on meander slip-off slopes also increases the height of flood plains.
Flood plains are created by meander ________close to the mouth.
Migration
What is meander migration?
consists of bank erosion on the outside bank of curved channels and point bar and floodplain building on the inside bank.
Flood _____are the wide valley floors that surround rivers in their ______courses.
- plains
- lower
What is a levee?
is an elongated naturally occurring ridge or artificially constructed fill or wall that regulates water levels. It is usually earthen and often parallel to the course of a river in its floodplain or along low-lying coastlines.
How are levees created?
Levees are created naturally during floods.
When a flood happens, water overflows over the banks of a river.
The larger sediments that were being transported by the river will be deposited first.
After lots of floods, levees (which are natural piles of sediment) are created at the side of the river.
Which of the following describes levees?
Piles of sediment
____ are piles of sediment that form at the side of river channels after repeated_____
Levees
-flooding