Rivers
Erode, Transport and Deposit
Terms, processes and features
The Work of Rivers
3 functions of rivers
Weathering of rock and soil.
Movement of eroded material.
Laying down the load of eroded material.
Processes of Erosion
How a river erodes
The Work of Rivers
Processes of erosion:
The force of the moving water causes erosion of the river bed and the banks of the river. The greater the speed and amount of water the greater the force.
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HYDRAULIC ACTION
The Work of Rivers
Processes of erosion:
2. Abrasion
The rivers load is bounced and dragged along the river bed causing it to scrape and deepen the course of the river.
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ABRASION ACTION
The Work of Rivers
Processes of erosion:
3. Attrition
The rivers load is constantly colliding in the moving river water causing the load to break down into smaller pieces.
The Work of Rivers
Processes of erosion:
4. Cavitation
As a river flows over the uneven river bed air bubbles travel up to the top of the river, pop and send ripples out towards the river banks. These ripples gently erode the rivers banks.
The Work of Rivers
Processes of erosion:
5. Solution
Chemicals in the rivers water and rocks along the river course change the river chemically which reacts with and erodes various rocks along the way.
CLICK ON THE IMAGE BELOW TO VIEW
A SHORT VIDEO ON THE VARIOUS FORMS
OF EROSION JUST MENTIONED
Three things you need to know……
Volume
Velocity
Bedrock
The amount of water in the river
The speed of the river….depending on the slope
Can influence the river…porous (permeable) rock means water can seep down through the river bed, lose volume and hydraulic action and the power to erode.
Transport
How a river moves its load
How does a river move its load?
River transportation
…..and?
River Terms
Three stages of a river
Youth Stage =
Mature Stage =
Old age Stage =
Three stages of a river
Upper Course
Middle Course
Lower Course
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TO VIEW A SHORT VIDEO ON
VARIOUS PARTS OF A RIVER.
Features
F.E.E.D
F: Feature (Name, erosion or deposition, stage it is found)
E: Explain with at least one or two processes explained
E: Three examples, one Irish
D: Clear 1/2/3 diagram/s to show how the feature is formed.
Describing a feature
Youth Stage =
Mature Stage =
Old age Stage =
Three features we will study
Waterfalls
Meanders and Oxbow Lakes
Deltas
Features of the Youth Stage
A typical upper course V-Shaped valley with interlocking spurs, steep valley sides and active slope processes.
The diagram below shows the formation of interlocking spurs.
Interlocking spurs
1
2
3
4
Feature of Erosion
Name
Found
Processes involved
Waterfall
Youth Stage
Hydraulic Action
Abrasion
CLICK HERE TO VIEW A
SHORT VIDEO ON WATERFALLS
Eddying
Hydraulic action
Abrasion
Bands of hard and soft rock
Resistant and less resistant rock
Headward erosion
Vertical erosion
Undercutting
Plunge pool
Cateracts
cascades
Notch
Swirling
Load
Youth stage
Back wall
Splash back
Differential erosion
Retreating waterfalls
Waterfall Terms
A waterfall is a feature of erosion found in the youth stage of a river.
Waterfalls are found in areas with bands of hard and soft rock (otherwise known as resistant and less resistant rocks). The hard rock takes longer to erode than the soft rock (differential erosion) so the river erodes the land at different rates. The river erodes the soft rock by the main processes of erosion including Hydraulic Action (the force and power of the moving river) and Abrasion (the scraping of the load against the bed and banks).
At first a small notch is created in the bedrock. This is a groove or dip in the soft rock. The notch may only be a few inches of a drop yet it increases the speed of the river falling over the edge. This encourages the river to erode vertically (downcutting) into the soft rock creating a vertical drop.
Over time the waterfall deepens as the soft rock is continuously eroded. At the base of a waterfall a rounded pool is found. This is called a plunge pool. The force of the falling water causes the water to swirl in the pool in a movement called eddying.
As the water falls the hydraulic action may cause water to splash back against the back wall causing further erosion. This causes undercutting of the back wall. Finally the overhang of hard rock is unstable and unsupported due to undercutting. It collapses and the rocks fall into the plunge pool.
Waterfalls continue to erode backwards in a process called headward erosion. This is when the hard and soft rock is all worn away and the river returns to its original slope.
There are two main types of waterfall:
Cataracts are large vertical falls of water and cascades are waterfalls that fall over a series of smaller steps or drops.
Waterfall formation
Look at the diagram, How is a waterfall formed?
Angel Falls, Venezeula
Victoria Falls, Zimbabwe
Examples
Niagara Falls, Buffalo, NY, USA
Can you put the labels below into the correct place on he diagram?
1
2
3
4
5
Features of the Mature Stage
A meander is a pronounced curve in the river (a bend).
As the river swings around a meander the speed of its flow is different on the outside of the river compared to the inner curve.
This is due to friction between deposited material on the inner curve which slows the flow of the river.
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SHORT VIDEO ON MEANDERS IN RIVERS
erosion
erosion
erosion
Deposition
Deposition
Deposition
Can you match up the labels to the correct place on the diagram?
faster velocity
undercutting
river cliff
outer bend
inner bend
slip-off slope
area of deposition
Meanders
1
2
3
Ox Bow Lake Formation
Can you look at the diagram & explain the formation of ox-bow lakes?
Ox Bow lake on Mississippi
Meanders and Ox bow lakes
Stage:
Processes involved:
3 main examples of meanders/ox-bow lakes:
Middle to old age
Erosion and Deposition
Mississippi River, Amazon River, Yangtze River
Deltas
CLICK THE GIF ABOVE TO VIEW A TIMELAPS VIDEO OF A DELTA FORMING IN A LAB.
MAJOR DELTAS OF THE WORLD
NILE DELTA, EGYPT
MISSISSIPPI DELTA, USA
AMAZON DELTA, BRAZIL
THE
END