River erosional landforms ( and landforms formed by both erosion and deposition)

where are waterfalls and gorges found

upper course of river where the river flows over an area of hard rock followed by an area of softer rock

How does a waterfall form?

1. river flows over an area of hard rock followed by an area of soft rock

2. the less resistant soft rock is eroded by hydraulic action and abrasion creating a step in the river

3. as water goes over the step it erodes more and more of the softer rock

4. a steep drop is eventually created which is called a waterfall

how is a gorge formed from a waterfall

1. the hard rock is eventually undercut by erosion, it becomes unsupported and collapses due to gravity

2. the collapsed rocks at the foot of the waterfall are swirled around and they erode the softer rock by abrasion, creating a plunge pool

3. over time more undercutting causes more collapses. The waterfall will retreat leaving behind a steep sided gorge

How do interlocking spurs form?

-In the upper course of a river, most of the erosion is vertically downwards, creating steep-sided V shaped valleys

-Rivers aren't powerful enough to erode laterally (sideways), they have to wind around the high hillsides that stick out into their paths on either side

-These hillsides that interlock with each other ( like a zip from above) as the river winds around them are called interlocking spurs

what are meanders

Large bends in a river

where do meanders form

Middle and lower course

how do meanders form

1. the river current is faster on the outer bend of the river so more erosion by hydraulic action and abrasion takes place forming river cliffs

2. the current is slower on the inner bend because the water is shallower

3. so eroded material is deposited on the inside of the bend forming slip off slopes

why is the river current faster on the outer bend

the river current is faster on the outer bend of the river because the channel is deeper and so there's less friction to slow the water down

how do oxbow lakes form from meanders

1. erosion causes the outside bends to get closer until there's only a small bit of land left between the bends called the neck

2. the river breaks through this neck usually during a flood and the river flows along the shortest course

3. deposition eventually cuts off the meander forming an ox-bow lake