Slide 2:
waterfalls
Slide 3:
Waterfalls Waterfalls generally form when hard resistant rock is above a softer and less resistant rock.
The softer rock is eroded faster by the river through hydraulic action and abrasion.
Process of forming a waterfall: The softer rock is eroded and begins to undercut (Through splash back)the harder rock, leaving an overhang.
Eventually this overhang collapses leaving boulders at the base of the overhang.
The force of the water, through hydraulic action creates a deep basin called a plunge pool.
This process is repeated many times and will cause the waterfall to retreat upstream, creating a gorge or a valley with steep sides.
Slide 4:
How A Waterfall Forms A Waterfall… But on a much larger scale
Niagara Falls
Canada
Slide 5:
erosion
Slide 6:
Erosion There are 4 main types of erosion in a river and these are:
Hydraulic Action – The force of the water on the bed and banks of the river. This breaks away areas of the banks and other material found in the river
Abrasion – Pebbles and boulders are carried along by the river’s flow, and they rub against the bed and the banks of the river and wears both the rocks and the river banks down. This is also known as Corrasion.
Corrosion – Rock minerals dissolve into the river, which sometimes make the water slightly acidic. This acidity makes the river dissolve some materials.
Attrition – The material being carried by the river collides and rubs with eachother, breaking itself into smaller pieces which have rounded edges. Eventually the material is reduced to silt particles.
Slide 7:
meanders
Slide 8:
Meanders Meanders in a river are simply curves or bends in a river.
Meanders are formed when a river begins to use surplus energy.
The energy is transferred to the outer bank, which is eroded faster by lateral erosion, causing a bend. Material is deposited on the inner bend, forming a River Beach/Slip-Off slope. Inner Bend Outer Bend
Slide 9:
Meanders Formation The outer bank of the river is eroded heavily by surplus energy.
This causes undercutting of the banks on the outer bank and a slip off slope on the inner bank from deposition due to low flow.
The undercutting forms a steep sided river cliff and a river beach. This happens because of helicoidal flow.
Slide 10:
Ox-bow lakes
Slide 11:
Ox-Bow Lakes Ox-Bow Lakes are formed by:
A meander is formed through helicoidal flow.
Erosion and deposition continue, and the bend becomes tighter and tighter until it becomes a tight loop.
When the water level is high and has a high flow, the water can pass straight over the neck of the meander rather than go around the loop. This is called a meander cut-off. The river keeps to its new channel, leaving the meander as a lake. This is called an Ox-Bow Lake as it is shaped like an Ox-Bow.
After a while the Ox-Bow lake will silt up and dry out. Vegetation will begin to grow in the lake.
Slide 12:
Thanks for Watching!