Formation of a meander + oxbow lake Flashcards
Pools and riffles…
A meander is produced by a stream/river swinging from side to side over POOLS (deeper areas of water) and RIFFLES (shallower areas of water where sediment is deposited that has greater turbulence.
Pools and riffles affect the speed and depth of the river channel.
Erosion of bank..
As it swings from side to side, it erodes the river sides through HYDRAULIC ACTION (sheer force of water breaks apart rocks and air bubbles in the water get into rocks and crack them) and CORRASION ((abrasion) where rock scrapes and wears away the river bed)
Increase in erosional power..
The water is forced to the outside of the bend as it swings from side to side, and subsequently speeds up, causing the sides to become eroded as EROSIONAL POWER INCREASES on the outside bend
HELICOIDAL FLOW
As the water winds around the bends, HELICOIDAL FLOW moves water and materials around bends and deposits it where the river is flowing more slowly on the inside bend, therefore BUILDING UP BEACHES and sand banks.
Migration of meander
Over time, the meander will move downstream as erosional processes continue, migrating from side to side
Oxbow lake
1) Process of river narrowing
After continued erosion to the meander, the neck of the RIVER IS NARROWED as the outside bend is eroded and materials are deposited on the inside bend
Oxbow lake
2) Cause of oxbow lake
During a storm or flood, the amount of water in the river can become too much for the river as there’s too much energy and water, so the river takes the most DIRECT ROUTE, straight through the neck of the meander
The curve of the meander is CUT OFF as the flow of water is directed in a more straightforward route
Oxbow lake
3) Blocking off of oxbow lake
The river slows now and so DEPOSITION OCCURS, which will over time block off the curve of the meander as ALLUVIAL BUILDS up on the banks, and the curved neck is blocked off, becoming an oxbow lake that will eventually dry out as its water source is lost
