Tectonic Hazards - Theory of Plate Tectonics

Tectonic Plate Movement:
  • The continents were once joined together, due to tectonic forces the land separated. Today, however, the continents are still moving slowly. At first, the whole world was known as Pangaea when the continents were all joined together 225 million year ago
  • Differences in heat mean the mantle flows in huge circles (convection currents).
  • The moving mantle drags the tectonic plates of earth’s crust (slabs) – called slab pull.
  • Currents move apart at constructive/divergent boundaries. This called sea-floor spreading if under the ocean.
  • Plates move together at destructive/ convergent margins due to the ‘slab pull’ forces. The area where one plate goes under another is called the subduction zone.
Convection Currents In The Mantle:
  • Therefore ultimately, the world’s tectonic processes and hazards result from the earth’s molten interior moving plates (the moon has a cold solid core, therefore no tectonic hazards)
Summary:
  • Mantle is semi-molten rock and this is where connection currents occur
  • Outer solid core lithosphere is the earth’s crust
  • Plates move due to slab pull (sea-floor spreading) (constructive) and subduction (destructive)
  • Continental crust e.g Africa, Asia is thicker and lighter than oceanic crust e.g Pacific and Atlantic oceanic crust.
Evidence Of Tectonics:
  • Volcanoes, Earthquakes & Tsunamis,
  • Continental Drift
  • Ocean Ridges
  • Ring Of Fire
  • Trenches
  • Fold Mountains
  • Hotspots
  • In 1912 Wegener started the theory of continental drift
  • In 1963 and theory of sea floor spreading started/accepted.
Palaeomagnetism:
  1. Sea floors spread, lava from divergent margins cools along the Mid-Atlantic Ridge
  2. When it cools, it has a magnetic signature
  3. Every few million years, the magnetic poles of the earth flip so the magnetic signature reverses.
  4. Creates lines moving out from the Mid-Atlantic Ridge of changing signatures and was then measured by scienstists, therefore, proving the sea floor is spreading.
Key Words:
Benioff Zone: Where the subducting plate is melting
Focal Depth – How deep the focus is
Focus – Centre of release of pressure energy and seismic waves of the earthquake
Epicentre – point on the earth’s surface directly above the focus.
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