Rivers and coasts

• How are meanders formed?

  • current is faster on the outside bend because the river channel is deeper
  • so more erosion takes place on the outside of the bend, forming river cliffs
  • current is slower on the inside of the bend because the river channel is shallower (more friction)
  • so eroded material is deposited on the inside of the bend, forming slip off slopes
• How are oxbow lakes formed?

  • formed from meanders
  • erosion causes outside bends to get closer until there is only a small bit of land left between the bends
  • river breakers through this land, usually during a flood and the river flows along the shortest course
  • deposition eventually cuts off the meander, forming an ox-bow lake
• When does a river deposit material?

  • when it loses energy
  • or slows down
• How is material transported along the coast?

  • by long shore drift
  • the gradual zig zag movement of sediment along a coast. caused by waves carrying material up the beach at an oblique angle, then back down at a right angle
  • waves follow the direction of the prevailing wind
  • swash carrier material up the beach in the same direction as the prevailing wind
  • backwash carried material down the beach
• what is freeze-thaw weathering + describe the process.

  • a type of mechanical weathering
  • happens when the temperature alternated above and below 0C
  • water enters rocks that have cracks eg granite
  • when the water freezes it expands, putting pressure on the rock
  • when the water thaws it contacts, which releases the pressure
  • repeated freezing + thawing widens the cracks and causes the rock to break up
• what is mechanical weathering?

  The breakdown of rock without changing it’s chemical composition.
• what is carbonation weathering + describe the process.

  • a type of chemical weathering
  • happens in warm and wet conditions
  • rainwater has carbon dioxide dissolved in it, which makes a weak carbonic acid.
  • carbonic acid reacts with rock that contains calcium carbonation eg carboniferous limestone, so the rocks are dissolved by the rainwater
• what is chemical weathering?

  the breakdown of rock by changing its chemical composition
• How are headlands + bays formed?

  • form along discordant coastline (made up of alternation bands of hard + soft rock at right angles to the coast)
  • alternating bands of resistant rock and less resistant rock
  • the less resistant rock is eroded faster, forming a bay with a gentle slope
  • because resistant rock erodes more slowly it juts out, forming a headland which steep sides