Physical Landscapes In The Uk-[optional] rivers Flashcards
Define ‘long profile’?
The change in the gradient of the river course from the upper course to the lower course.
What is a ‘cross profile’?
A cross section of the river - this shows a ‘slice’ of the river valley and channel
What is a V-Shaped valley?
A valley with steep sides and a narrow bottom that has been formed by erosion
What is a tributary?
A smaller river or stream flowing into a larger river
What is a confluence?
The point where two rivers meet
Define ‘load’
The amount of material carried by a river
What is ‘sediment’?
Material such as sand and clay that is carried by a river
What are the characteristics of the upper course of a river?
- Steep gradient
- Narrow v-shaped valley
- Narrow/shallow river
- Large angular sediment load
- Mostly erosion taking place
What are the characteristics of the middle course of a river?
- Shallower gradient
- Asymmetrical valley cross section
- Deeper river
- Smaller/rounded load
- Balance between erosion and transportation taking place
What are the characteristics of the lower course of a river?
- Very low gradient
- U-shaped valley
- Wide/deep river
- Small suspended load
- Mostly deposition taking place
Define ‘erosion’?
The wearing away of rock by the natural processes of rivers, ice, wind and sea
Name the 4 processes of river erosion
- Abrasion
- Attrition
- Hydraulic Action
- Solution
Define ‘hydraulic action’
Fast flowing water pushes air into cracks and the force of this causes the banks to break up over time
Define ‘abrasion’
Sand and pebbles are dragged along the river bed, wearing it away
Define ‘attrition’
Rocks and stones wear each other away as they knock together
Define ‘solution’ (erosion)
Rocks such as limestone are dissolved in acid rainwater
Define ‘transportation’?
The movement of eroded material by natural processes such as wind, rivers and sea
Name the 4 processes of river transportation
- Traction
- Saltation
- Suspension
- Solution
Define ‘traction’
Big boulders and stones are rolled and dragged along the river bed
Define ‘saltation’
Stones and pebbles bounce along the river bed
Define ‘suspension’
Smaller particles and stones (e.g. sand and silt) are carried along in the rivers flow.
Define ‘solution’
Some material is dissolved into the river water and transported this way
What does ‘deposition’ mean?
When a river drops the sediment that it is carrying
Why will a river deposit its load?
- Drier weather (less water so less energy)
- River slows in speed (less speed so less energy e.g. inside bend of a river)
- River floods (water onto the flood plain and deposits layers fine silt and clay [this is known as alluvium] which is fertile and good for farming)
Name the river landforms formed by erosion
- Waterfalls
- Gorges
- Interlocking spurs
Name the river landforms formed by erosion and deposition
- Meanders
- Ox-bow lakes
Name landforms created by deposition
- Floodplains
- Levees
Name the landforms found in the upper course of a river valley
- Waterfalls
- Gorges
- Interlocking Spurs
- Rapids
What is a waterfall?
A vertical fall of water where the course of a river is interrupted by a steep drop in the land it is flowing over
How does a waterfall form?
- Water flows over harder rock followed by softer rock
- The softer rock underneath the harder rock will erode over time (hydraulic action and abrasion) creating a step in the river
- The hard rock is undercut by erosion.
- Eventually the hard rock will collapse as it is now unsupported creating a deep plunge pool.
- The process will continue over time creating a steep sided gorge
What is a gorge?
A steep-sided cut through the landscape formed over thousands of years by a retreating waterfall
What is a plunge pool?
The area of deep water at the bottom of a waterfall, formed by hydraulic action and the grinding of rocks and pebbles
What are ‘interlocking spurs’?
Interlocking’ hillsides that look like a ‘zip’ formation.
How are interlocking spurs formed?
In the upper course, rivers aren’t powerful enough to erode laterally, so they wind around the hillsides creating a zig-zag shaped flow.
Name the landforms found in the middle course of the river
- Meanders
- Ox-bow lakes
Define ‘helical flow’?
The corkscrew pattern of flow found in a river
What is the thalweg?
The line of fastest flow in a river
What is a meander?
A pronounced bend in a river
What is an ox-bow lake?
A horse-shoe shaped lake shaped that is formed when a river bend is cut off from the main river and becomes isolated
Explain how an ox-bow lake forms
- The fastest flow of water is on the outside bend of the river
- This results in erosion. The outside bends move closer together as the meander neck becomes narrower.
- When there is a very high discharge, the river cuts across the neck and takes a straight course. The former meander is left as a horseshoe shaped ox-bow lake.