formation of river landforms Flashcards
Interlocking spurs
As the river erodes the Steep v-shaped valley in the upper course, it winds and bends to avoid areas of hard rock. The vertical erosion due to gravity creates interlocking spurs, which jut out alternatively.
v-shaped valley
Vertical erosion dominates in the upper course of a river due to gravity.
Hydraulic action erodes downwards into cracks in the riverbed.
Fallen rocks cause abrasion, deepening the valley.
Steep sides collapse over time, forming a V-shaped valley.
Waterfalls
Waterfalls form where a river flows over bands of hard rock overlying softer rock.
The softer rock is eroded more quickly by hydraulic action and abrasion, creating a step.
Water plunges over the step, forming a deep plunge pool.
Erosion undercuts the soft rock beneath the hard rock, creating an overhang.
The overhang eventually collapses due to lack of support.
The waterfall retreats upstream, leaving behind a steep-sided gorge.
Meanders and Oxbow Lakes
In a bend, water flows fastest on the outside, causing erosion by hydraulic action and abrasion.
This undercuts the riverbank, forming a river cliff and deepening the channel.
On the inside bend, water flows more slowly, leading to deposition and the formation of a slip-off slope.
Over time, continued erosion on the outside and deposition on the inside exaggerates the bend into a swan-neck meander.
During a period of high flow, the river breaks through the narrow neck, taking the shortest route.
Deposition later seals off the old meander, forming an oxbow lake.
Levees
Levees are raised banks formed along rivers in the lower course during floods.
When a river floods, it loses energy and deposits its load.
Heavier material is deposited first near the riverbanks; finer material is carried further onto the floodplain.
Repeated flooding builds up the heavier material, forming natural embankments.
Floodplains
Floodplains are wide, flat areas of land next to the river, found mainly in the lower course.
They form when the river floods and deposits alluvium across the valley floor.
Lateral erosion by hydraulic action and abrasion widens the valley over time.
Meander migration also contributes to the widening of the floodplain.
Estuaries
Estuaries form at the river mouth where rising sea levels have flooded the river valley.
They are intertidal zones where river and sea water mix.
At low tide, the river loses energy and deposits sediment.
Over time, sediment builds up to form mudflats and saltmarshes.
