Physical geography - Rivers

Question 1

What are the 3 sections of a river called?

Answer 1

Upper course
Middle course
Lower course

Question 2

Describe the features of the upper course of a river

Answer 2

River starts as many tributaries, which are narrow and v-shaped. Each tributary doesn’t carry a lot of water, but combined tributaries all fill up the river channel further down. The sides of the tributaries tend to be like a valley, with large gradient either side so water can run into the tributary.

Question 3

Describe the features of the middle course of a river

Answer 3

Tributaries merge together to form a channer, which is rounder in shape and deeper. The more water that passes by, the larger the energy of the water, do more erosion can take place to widen the channel. The area around the river channel is flat and low-lying which is the floodplain if the river needs to flood.

Question 4

Describe the features of the lower course of a river

Answer 4

River carries the largest volume of water in a very wide and deep channel. There are ridges either side of the river banks called Levees. The size of the valley has increased, so it is even wider and flatter than the middle course.

Question 5

What is the speed of water like in the upper course?

Answer 5

Channel is shallow, so most of the water passes the riverbed at a slowing rate of flow due to friction. As the river channel gets bigger, less water is in contact with the riverbed, which means the velocity of water increases.

Question 6

What is the speed of water like in the lower course?

Answer 6

A lot faster as there is less friction with the river bed. River is wider and deeper due to increased erosion that’s occurred from fast water.

Question 7

What are the erosional processes that take place in a river?

Answer 7

Abrasion
Attrition
Hydraulic Action
Solution
- majority takes place in upper and middle course. Can take place downwards (vertical erosion) or sideways (lateral erosion)

Question 8

Describe the process of Abrasion

Answer 8

Where rocks carried by water (load) scrapes and bangs against the sides of the river, so wear away the channel gradually (like sandpaper)

Question 9

Describe the process of Attrition

Answer 9

Rocks and pebbles hit against each other, wearing each other down and becoming rounder and smaller. It changes the size of the load, but doesn’t affect the shape of the river channel

Question 10

Describe the process of Hydraulic Action

Answer 10

Water under high pressure causes cracks to force apart an widen in rocks along the banks of the river. Over time, this causes rocks to fracture and collapse into the river, expanding the channel.

Question 11

Describe the process of Solution (erosion)

Answer 11

The river gradually dissolves chemical compounds in rocks that it flows over, e.g. limestone can dissolve gradually into the river, if the river water is slightly acidic (due to acid rain)

Question 12

What transportation processes take place in a river?

Answer 12

Solution
Suspension
Saltation
Traction

Question 13

Describe the process of Solution (transport)

Answer 13

Chemicals dissolved in river water

Question 14

What is suspension?

Answer 14

Particles and small rocks that a light enough to float within the water.

Question 15

What is saltation?

Answer 15

Pebbles and small rocks which are too heavy to be suspended bounce along the river channel

Question 16

What is traction?

Answer 16

Large rocks are rolled along the riverbed

Question 17

What is deposition?

Answer 17

Dropping of river’s load when water in a river decreases in speed.
- Heaviest materials get dropped first e.g. rocks and stones are deposited in the upper course, whereas finer sediment travels as far as the lower course before being deposited.

Question 18

What are some erosional landforms of rivers?

Answer 18

Interlocking Spurs
Waterfalls
Gorges

Question 19

What are interlocking spurs and how are they formed?

Answer 19

Found in the upper course of the river where water doesn’t have a lot of energy, so isn’t very powerful. Low energy means water isn’t strong enough to erode resistant rocks in the spur, instead, the river re-routes and curls around them.
The spurs are the bits of mountain to the left and right of the river which point down towards it.

Question 20

What are waterfalls and how are they formed?

Answer 20

Waterfalls occur when water flows over rocks with different resistances to erosion.
As the soft rock erodes more quickly than hard rock, over time, it will create a step around the hard rock. The soft rock will continue to erode, undercutting the hard rock. The hard rock is left suspended in the air as an overhang. The rotational movement of the water quickens erosion, creating a deep plunge pool. Due to force of gravity, the unsupported overhang collapses. The broken up rocks fall into the plunge pool, which act as tools for erosion and deepen the plunge pools - erosion continues to undercut underneath the hard rock, creating an overhang again. The continual process of the overhang collapsing causes the waterfall to retreat upstream over time The plunge pool continues to deepen, and the hard rock continues to be undercut to create an overhang.

Question 21

What is a gorge and how is it formed?

Answer 21

Form from water falls - as the waterfall retreats upstream, it leaves behind a steep valley carved into the rock with the river running along the base.

Question 22

What are some landforms due to erosion and deposition combined?

Answer 22

Meanders
Ox Bow lakes

Question 23

What are meanders and how are they formed?

Answer 23

Bends in the shape of the river, often found in the middle course.
Water travels faster outside the bend, which means lateral erosion takes place there. This leaves a river cliff, as material falls into the river and gets transported downstream. On the opposite side, the water travels slower and changes direction sharply, so loses energy and deposits sediment. Hence, erosion wears away the outer edge of a bend and deposition creates a slip-off slope on the inside of the bend.

Question 24

What are Ox-bow lakes and how are they formed?

Answer 24

In the beginning, the river has meanders that form depending in the speed of the water. Erosion happens when the fastest water hits the sides of the meander, whereas deposition occurs on the inside of the bend, where water is slowest. Gradually, erosion bends the river so that the meanders travel towards each other. The neck of the meander will eventually break, causing a straight river and a bend where water is slow if not stationary. The old meander becomes separated from the main river as material gets deposited at the top, creating a separate ox-bow lake