Earth Movements

Interior Structure of the Earth

The Crust

  • The crust on which we are is approximately 64 km thick under land areas to as little as 12 km thick under sea areas.
  • The upper layer of the crust is made mostly of silicon and aluminium, and is rigid.
  • The lower layer of the crust is made of silicon and magnesium, and is plastic.

The Mantle

  • The mantle is beneath the crust, and is about 3 000 km thick.
  • It is made of mostly iron and magnesium.
  • It is plastic like putty, and continually changes shape due to heat and pressure.

The Core

  • The core extends from 3 000 km beneath the Earth's surface to the centre of the Earth.
  • The outer layer of the core is liquid molten rock, and is about 2 000 km thick.
  • The inner layer of the core is solid rock, and is about 1 500 km thick.
  • The core is mostly iron, nickel and cobalt.

Crustal Plates

Theory of Plate Tectonics


  1. Granite - volcanic rock with large crystals formed by slow cooling of magma beneath the Earth's surface
  2. Basalt - volcanic rock with small crystals formed by rapid cooling of lava on the Earth's surface
  3. Pumicestone - volcanic rock filled with air bubbles formed by the ejection and rapid cooling of lava in the air
  1. A crater lake may form when rain fills the cooled volcanic crater.
  2. If the volcano sides erode over time leaving the solid vent, mountains such as the Glasshouse Mountains are formed.
  3. If a volcano has not erupted in a long time but may erupt again, it is said to be dormant (sleeping).
  4. If a volcano has not erupted in a very long time and probably will not erupt again, it is called extinct.
  1. Shield Cone - Wide at the base with gentle slopes, formed by gentle volcanoes
  2. Cinder Cone - Narrow at the base, steep slopes built up by angular interlocking cinders (ash), formed by explosive volcanoes
  3. Composite Cone - Intermediate between the shield and cinder cones, built up from alternating layers of lava and cinder
  4. Dome Mountain - Magma pushes up through sedimentary rock


  1. P Waves - Primary or push waves that travel deep beneath the Earth's surface at about 5.5 to 13.5 km/s
  2. S Waves - Secondary or shake waves that travel deep beneath the Earth's surface at about 3.7 to 7 km/s
  3. L Waves - Longitudinal waves that travel along the Earth's surface at about 3.2 km/s, causing greatest damage to buildings, landslides and tsunamis (tidal waves)




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