formations

• formation of a v-shaped valley

  - water eroded vertically into a river bed by hydraulic action and abrasion

  - weathering (freeze thaw weathering) breaks up the rocks on the valley sides

  - the rock falls due to gravity into the river

  - the rocks are carried by the river downstream, and a v-shaped valley remains
• how are waterfalls formed

  - river flows over band of hard rock and soft rock

  - the soft rock erodes quicker, leaving an undercut of the soft rock and an overhang of the hard

  - turbulent falling water encourages a splashback, causing more erosion

  - eventually, the overhand will collapse due to gravity, and will fill in the undercut to leave a plunge pool

  - this process continues and retreats back, creating a steep sided gorge / waterfall
• formation of a ox-bow lake

  - the neck of a meander is slowly eroded away due to hydraulic action and abrasion

  - this erosion continues until the neck breaks and the water runs straight through

  - because this new straight channel is the path of least resistance, majority of the water flows that way, eventually causing a cut off to where to original meander was as it is no longer being uses

  - leaves a horse-shoe like shape called an ox-bow lake
• how are levees formed

  - during a flood, silt is deposited on a floodplain

  - the heaviest more coarse sediment is deposited at the channel edges, whereas finer particles of sediment are on the outer parts of the floodplain

  - with every flood the banks are built a little higher and leaves natural levees

  
• mass movement

  occurs when weathered material moves downhill under the force of gravity
• factors that affect mass movement

  - rock type

  - rock structure
• types of mass movement

  - rockslides

  - rockfalls

  - slumping
• rockslides

  - if the rock layers dip into the sea (diagonal layers), a more gentle sloping cliff forms

  - waves erode the bottom of the cliff, and the undercutting leaves large slabs sliding down

  
• rockfalls

  - if the layers of rock are horizontal, steep cliffs form

  - erosion at the foot of the cliff causes undercutting at the base of the cliff face along bedding planes

  - eventually, the overhang of the top rock becomes so big that the cliff is unsupported and it collapses

  
• slumping


  - this is common when the rock is weaker and is made up of sand and clays

  - here, water can soak into the sand layer, making it heavier, whilst the impermeable clay allows water to lubricate between the joint layer, causing it to move

  - this is called slumping as the cliff then collapses with a curved action

  
• wave cut platforms formation

  - bedding planes and joints are exploited by the sea

  - erosion via hydraulic action and abrasion cause the rock overhangs to create a wave cut notch

  - eventually the overhang collapses due to gravity

  - this process continues and the cliff retreats and leaves a wave cut platform

  
• CASS sequence

  - points of weakness like bedding planes and joints are exploited by the waves via hydraulic action and abrasion ~ weathering also contributes

  - continued erosion from the sea eventually cuts deeper into the rock and forms a cave

  - the erosion cuts so deep and eventually the rock breaks through to leave an arch

  - prolonged erosion and weathering widens the arch, until there is no longer enough support and the top of the arch collapses due to gravity to leave a stack

  - the same erosion now undercuts the base of the stack, until that eventually collapses as the base of support is lost to leave a stump
• longshore drift

  the lateral movement of sediment

  - moves up the beach at an angle (not 90°)

  - then moves down the beach at a right angle due to gravity

  
• formation of a spit

  - the longshore drift transports sediment along the coast

  - when there is no more land, waves lose energy, causing the sediment to be deposited

  - this sediment accumulates, creating a spit

  - the change in wind direction forms hook like shapes in the deposited sediment

  - the flow on the estuary is too strong so the deposition stops (stops growth of the spit)

  - behind the spit, sand is protected and sheltered, resulting in the formation of a salt marsh
• formation of bars

  - occurs within the formation of a spit but there is so estuary to stop its growth

  - the longshore drift continues the act along the coastline and when it reaches the gap in land a spit will start to form

  - the spit continues to form until it reaches the land, cutting the bay off from the ocean

  - just behind the spit is a salt marsh, but now behind that as well we now have a lagoon

  - overall, this means a bar has been formed
• what do sand dunes need to form

  - a large flat beach

  - a large supply of sand

  - a large tidal range so that there is time for the sand to dry

  - onshore winds to move the sand to the back of the beach

  - obstacles (eg. driftwood) for the dune to form against
• 3 ways wind moves sand

  - creeping (4% of movement) ~ sand grains collide with each other and push other grains along

  - saltation (95% of movement) ~ grains of sand bounce along in the wind as they are raised and dropped

  - suspension (1% of movement) ~ sand is picked up and carried within the wind