Unit 1C - River Landscapes in the UK - River landforms of erosion and deposition Flashcards
Name landforms found in upper course?
Inter-locking spur, V-shaped valley, waterfall and gorge
What is needed to create waterfall?
Hard rock followed by and over soft rock
What is created when waterfall retreats?
A steep sided gorge
How does a waterfall form?
- softer rock eroded, by h-a and abrasion, more than hard rock, creating a ‘step’ in river
- as water goes over step, it erodes more and more of softer rock
- steep drop eventually created (waterfall)
How does a steep-sided gorge form from waterfall?
- hard rock eventually undercut by erosion and becomes unsupported and collapses
- collapsed rocks swirled around at foot of waterfall where they erode softer rock by abrasion, creating deep plunge pool
- over time, more undercutting causes more collapses. Waterfall will retreat, leaving a steep-sided gorge
What are interlocking spurs?
- in upper course, most of erosion is vertically downwards, creating steep-sided, V-shaped valleys
- rivers aren’t powerful enough to erode laterally and have to wind around high hillsides that stick out into their paths on either side
- hillsides interlock with each other as river winds around them
An area of hard rock around which the river winds
Name landforms found in middle course?
Meander and ox-bow lake
What is a meander?
A bend in a river
What happens on outside bend of meander? Why?
River flows fast and erodes creating river cliff, as channel is deeper so less friction to slow current down
What happens on inside bend of a meander? Why?
River flows slowly, depositing creating a slip off slope, as channel is shallower so more friction to slow current down
What happens to create an ox-bow lake?
River erodes through neck of a meander on outside bend or flood occurs cutting off meander
How does an ox-bow lake form from a meander?
- Meander gets larger over time and neck gets narrower due to continued lateral erosion through hydraulic action on outer bend
- river breaks through neck, either during a flood or erosion, and flows along shortest course
- deposition of rocks and soil at edges, cutting off meander and forming an ox-bow lake
How does a meander scar form from an ox-bow lake?
Ox-bow lake eventually dries up leaving a meander scar
Name landforms found in lower course?
Floodplain, levee and estuary
What is a flood plain?
A large flat area either side of a river channel that floods
2 things that build up flood plains?
- When river floods onto flood plain, water slows down and deposits eroded material that it’s transporting, building up flood plain.
- Meanders migrate across flood plain, making it wider, and downstream, flattening out valley floor. Deposition that happens on slip-off slopes of meanders builds up flood plain
Levees and floodplains are depositional features and occur when a river flood, why?
More water in contact with surface when it floods so increased friction which slows speed of water as energy being used to overcome friction
What are levees?
Natural embankments along edges of river channel
How do levees form?
- During a flood, eroded material deposited over whole flood plain. Heaviest material deposited closest to channel as it gets dropped first when river slows down.
- Over time, deposited material builds up, creating levees along edges of channel
Estuaries are created when?
When fresh and salt water meet at mouth and velocity falls as sea’s flow is slower than rivers’. As a result, sediment is deposited due to loss of energy
How do estuaries form?
- Found at mouth, where river at its widest. Water here is tidal and floods over river banks, carrying silt ad sand onto valley floor.
- as tide reaches its highest point, water moving very slowly so sediment deposited
- over time, more and more mud builds up, creating large areas of mudflats
- at low tide, these are exposed
On which river is landforms such as High Force Waterfall and Cross Fell at its source?
River Tees
