Geography

• A river flood is when the river bursts and spills over the surrounding land
• Flood plain


  • An area of flat ground next to a river, formed mainly of river sediments
  • A flood can last just a few days or several weeks
• Flood event


  Often caused by a combination of physical and human factors
• Physical causes of floods

  • Prolonged rainfall
  • Saturated ground
  • Low-lying land
  • High tides and storm surges from the Bristol Channel
• In January 2014 in Southern England, rainfall totaled 183% higher than average for that month
• The long period of rainfall caused the ground to become saturated so that it could not hold any more water
• The combination of impermeable bedrock (clay) and low interception levels (the grass) means that the area is at high risk of flooding
• Much of the area lies at, or just a few meters above, sea level, putting it at risk of flooding
• High tides and storm surges from the Bristol Channel prevent the floodwater from being taken to the sea, forcing it back up the rivers
• Human causes of floods

  • Lack of dredging over the years, causing the rivers to become clogged with sediment
  • Change in farming practices, with much of the land converted from grassland to grow maize, making it less able to retain water
• Dredging increases the ability of a river to carry more water
• A waterfall is formed when there is a layer of hard, resistant rock on top of a layer of soft, less resistant rock
• Hydraulic action and abrasion make a plunge pool at the base of a waterfall
• Retreat of a waterfall

  1. The overhanging hard rock falls into the plunge pool

  2. The position of the waterfall moves backwards (retreats)
• Inner core

  The hottest part of the Earth, made up of iron and nickel, with temperatures up to 5,500°C
• Outer core

  A liquid layer surrounding the inner core, also made up of iron and nickel, extremely hot
• Mantle


  The widest section of the Earth, made up of semi-molten rock called magma, hard in the upper parts but soft and beginning to melt lower down
• There are two main types of crust: continental crust and oceanic crust
• Formation of new mountains

  1. At the plate margin, the oceanic crust is being pushed downwards into the mantle

  2. It is dense (heavy), and so it falls below its normal level as it sinks into the mantle, creating a deep ocean trench
• Sedimentary rocks


  Rocks formed from sediments deposited on the sea bed in layers and compressed over millions of years
• Sandstone


  • Light brown, sandy in colour
  • Small grains
  • Permeable
  • Hard
• Metamorphic rocks


  Rocks that were once igneous or sedimentary rocks, changed by great heat and/or pressure
• Marble


  Metamorphic rock formed when limestone is changed by intense heating, melting the grains to form large crystals
• Marble


  • Large crystals
  • Often white-various colours
  • Very hard
  • Impermeable
  • Ornate
• Slate


  Metamorphic rock formed when mudstone (shale) is changed by intense pressure, causing the minerals to line up in thin layers
• Slate


  • Distinct layers
  • Easily split along cleavage lines
  • Dark grey/black colour
  • Very hard
  • Impermeable
• Liquefaction


  When an earthquake shakes wet soil, causing the water within to rise to the surface and turn the soil into a liquid mud
• As a result of liquefaction, foundations will be compromised and buildings will either sink or tip over
• Tsunami


  A large wave created due to an underwater earthquake, sending shockwaves into the water which cause a surge of water to build up and make its way towards the coastline
• The energy transferred into a tsunami wave can often be transported for thousands of miles across an ocean
• Possible effects of earthquakes

  • Faint tremor, no damage
  • Doors and windows rattle
  • Chimneys collapse, plaster cracks
  • Poorly-built structures collapse