River Landscapes: Processes (SQA National 5 Geography): Revision Note

Specification checklist

This page covers what you need to know from the SQA National 5 geography specification to answer questions on:

• The identification and formation of the following landscape features:

  • v-shaped valleys, waterfalls, meander, ox bow lake, levee

River weathering, erosion and transportation processes

Weathering and mass movement

• There are three types of weathering

• These happen in-situ

• Weathered material is then moved by mass movement into the river channel

Physical

• Rock is broken down into smaller pieces

• This occurs due to changes in temperature, such as freeze-thaw and exfoliation

Chemical

• Rocks disintegrate and dissolve in slightly acidic rainwater 

Biological weathering

• Rocks are broken apart by the roots of plants 

• Erosion is the wearing away and removal of material

• Four erosion processes change the shape of a river's channel:

  • Hydraulic action

  • Abrasion/corrasion

  • Corrosion/solution

  • Attrition

Hydraulic Action

• Hydraulic action is the sheer force of waves crashing against the riverbed and banks

• The power of the waves forces air into cracks, compresses it and this breaks the material of the banks apart

Abrasion/corrasion

• Rocks and pebbles carried in the river wear away the bed/banks as they scrape against them (the sandpaper effect) 

Corrosion/Solution

• When chemicals in the river water dissolve minerals in the river channel, causing it to break up

 Attrition

• When rocks and pebbles carried by the water smash into each other, they wear away and gradually become smaller, rounder and smoother

The formation of upper course river features

V-shaped valley formation

• In the upper course, the river uses energy for vertical erosion, cutting down into the landscape

• The river erodes a deep notch into the landscape through hydraulic action, abrasion and corrosion

• As the river erodes, the sides of the valley are exposed to freeze-thaw weathering

  • This loosens the rocks and steepens the valley sides

  • Any rocks which fall into the river are used in abrasion, which leads to further vertical erosion, creating a V-shaped valley

• The river transports the rocks downstream

Waterfall formation

• River erosion wears away the less resistant soft rock more quickly than hard rock, to form a step in the river

  • This is called differential erosion

• The falling water erodes a deep lake called a plunge pool through hydraulic action

• The swirling water causes corrosion and abrasion

• This undercuts the hard rock above

• There is nothing left to support the overhang of hard rock, so it collapses

• The process is repeated over time

• The waterfall retreats upstream,

• This leaves a gorge, a deep valley with very steep sides and a narrow valley floor 

The formation of middle course river features

Meander formation

• A meander is a bend in the river channel

• A river has more energy for lateral (sideways) erosion in the middle and lower courses

• The river contains areas of deep water and areas of shallow water, called pools and riffles

  • This results in areas of slower and faster water movement, meaning the current swings from side to side

•  In a meander, the water is pushed to the outside of the bend and greater velocity means the river has more energy to erode through abrasion

  • This forms a river cliff on the outside bend

• The river flows more slowly on the inside bend and deposits some of its load to form a river beach/slip-off slope

• Continuous erosion on the outer bank and deposition on the inner bank form a meander in the river 

The formation of lower course river features

Ox bow lake formation

• In its middle and lower courses, a river has more energy for lateral erosion

• In the lower course, meanders are larger

• Continual erosion on the outside of a river bend narrows the meander neck

• When the river floods, it takes the shortest, most direct route

  • The channel cuts through the neck of the meander

• Deposition occurs along the banks of the river, including the entrance and exit to the meander

  • Eventually, the meander is completely cut off to leave an ox bow lake

  • This is the old meander loop, separate from the main river channel

Formation of a levée

• During floods, rivers overflow their banks

• The water which flows onto the floodplain will initially slow down as a result of the friction between the water and the land

  • As the water slows, it will deposit the material it is carrying onto the floodplain

• The coarsest material will be deposited first, next to the river

• Over time, following multiple flood events, this builds up to form a natural embankment called a levée

• Smaller sediments are carried further away from the river and deposited over the outer parts of the floodplain