River Landscapes Flashcards
Why does freeze thaw weathering occur in the formation of a v shaped valley?
Because in the upper course temperatures are lower resulting in any water freezing and melting repeatedly and eventually loose rock falls into the river.
How are interlocking Spurs created?
River winds around a harder area of rock and leaves these areas sticking out
What does ‘load’ mean
The material carried by a river to be deposited or used for erosion
What does ‘potential energy’ mean in terms of the force of the river?
The higher up a river starts, the more energy in which it has to erode on the way down. Potential force of the river.
How are Rapids formed?
An area of harder and softer rock are side by side. The softer rock is less resistant and gets eroded through abrasion and corrosion and so Rapids are formed - a step in the river.
How does a waterfall develop on from Rapids?
Abrasion, hydraulic action and corrosion cause the softer rock to become undercut and the harder resistant rock is left overhanging the plunge pool. The plunge pool is deepened through attrition. The weight of the water causes cap rock to collapse - and the whole waterfall moves backwards - eventually creating a gorge.
Describe the formation of a meander
Development of pools and riffles causes friction and slows water down
This causes slight bends in the river
Bends are accentuated and corkscrew flow picks material up from the outside bank on one bend and deposits it on the other.
River runs slowest on shallow side and slip off slope develops through deposition.
Lateral erosion causes outside of the bend to be undercut by abrasion and and hydraulic action
This can cause river cliff to develop.
Describe the formation of an oxbow lake
Overtime, the neck of the meander becomes narrower due to continued lateral erosion.
During times of flood the river acts cuts through the meander neck by process of hydraulic action + abrasion. Sediment is deposited at the side, cutting off the loop, creating an oxbow lake.
- River takes shortest route cutting through the neck. This lake slowly dries up unless high rainfall occurs.
Describe the formation of a levee
During flood, when water loses energy, sediment is deposited as sorted material on a river bank.
The river bed rises and with each flood the levees grow taller and the river channel rises.
Describe the formation of a delta
When a river carrying sediment reaches a body of standing water - lake, ocean or reservoir - it enters and is no longer confined to its channel and expands in width, losing velocity.
As a result, sediment drops out of the flow and is deposited. Over time, this single channel will build a ‘deltaic lobe’ pushing its mouth further into the standing water.
Natural levees are breached during times of flood and a shorter route will be found. These additional channels are called distributary channels.
Describe the formation of a v shaped valley
On a slope the river erodes downwards. Slope processes assist by transferring weathered material down the valley sides to the bottom of the valley through freeze thaw action and slope weathering.
Weathered material is then removed by the river as its load is sharp and angular in the upper course.
