Geography

• Stronen Explain 2 reasons why some countries have low burth rates

  1. Women tend to marry later

  2. Preference for smaller families
• Population pyramids


  • Broad shape at the top shows high proportion of people living longer
  • Bulges show periods of immigration or baby booms
  • Indents show higher death rates from war, famine, disease or emigration
  • Wide base shows large number of children (high birth rate)
  • Narrow base shows small number of children (low birth rate)
• Ageing population

  Proportion of elderly people over 65 is increasing
• Youthful population


  Proportion of young people under 15 is high
• Hydraulic Action


  The power of water forces air into cracks in the banks and weakens them so they eventually collapse.
• Abrasion 


  The rocks and stones carried by the river wear away the bed and banks by scraping them. (they act like sandpaper)
• Attrition


  The particles carried by the river are bashed against each another, making them smaller and rounder.
• Solution


  The water dissolves soluble materials from the bed and banks. This helps them to break up.
• Traction


  Rolling large stones along the bed of the river.
• Saltation


  Bouncing smaller particles along the bed.
• Suspension


  Sediment that floats within the river flow.
• Solution 


  Minerals dissolved in the water.
• Lag time

  The time between the highest rainfall and the highest (peak) discharge.