chapter 8.2

• Ocean currents


  1. Wind blows from same direction for long time

  2. Seawater starts to flow
• Ocean currents


  • Can bring warmer water from tropics to polar regions
  • Can carry cold polar water to warmer zones
• Ocean currents


  Influence average temperature on land
• Gulf Stream


  Warm ocean current that flows past Norway, bringing warm water from Gulf of Mexico to west coast of Europe
• The Earth's crust is divided into tectonic plates
• Tectonic plate movement


  1. Plates can move apart (divergence)

  2. Plates can move towards each other (convergence)

  3. Plates can slide past each other (transform movement)
• Divergence


  • Magma rises up from mantle and flows away as lava, filling gap between plates and forming new crust
  • Creates mid-ocean ridges with low-lying areas in between
• Convergence - Oceanic plate and continental plate


  • Heavier oceanic plate slides under lighter continental plate (subduction)
  • Forms deep underwater trenches
• Convergence - Two oceanic plates


  • Older, heavier plate slides under younger plate
  • Forms deep underwater trenches
• Convergence - Two continental plates


  • Forms mountain ranges
• Transform movement


  • Plates slide past each other, e.g. San Andreas Fault
• Types of volcano


  • Stratovolcano (composite volcano)
  • Caldera volcano
  • Shield volcano
• Stratovolcano


  • Formed by subduction
  • Steep slopes
  • Made of layers of lava and ash
  • Thick, dense magma
  • Explosive eruptions when pressure is high
• Stratovolcano eruption


  1. Thick lava flows down slope

  2. Volcanic bombs, ash, toxic gas and steam fly high into air

  3. Pyroclastic flow races down slope

  4. Danger of deadly mudflows from melting ice and snow
• Caldera volcano


  • Large crater caused by collapse of empty magma chamber after eruption
  • Often has crater lake and new crater
• Shield volcano


  • Formed by plate divergence
  • Thin, flowing lava
  • Flattened slopes shaped like a shield
  • Non-explosive eruptions
• The Earth has existed for about 4.6 billion years
• Geological time chart


  Divides Earth's geological history into different periods
• Fossils


  Petrified imprints of plants and animals preserved in Earth's crust, used to determine geological period