Plate Tectonics and Associated Hazards- Revision Notes

Plate Movement

Earth Structure

The Earth is comprised is of three layers

The Core

The core comprises of dense rocksespecially of iron and nickel alloys. The inner core is solid and the outer core is liquid. The outer core is where the Earth’s magnetic fields originate, due to electrical currents flowing in the metallic core. Fluid moves due to convection currents. It is thought there is a radioactive decay happening in the core which powers the convection currents.

The inner core is 1100km deep. The outer core is 2400km deep

The Mantle

The mantle is less dense than the core as the rocks are comprised of lighter elements such as silicon and oxygen with varying densities depending on the proximity to the core. Close to the core rocks have a density of 5.7 and 3.0 near to the crust. The junction between Core and Mantel is known as the Gutenberg Discontinuity or Moho discontinuity the junction between the Mantle and Crust.

The Crust

Continental

Oceanic

Age

3800 million

200 million

Thickness

30-70km

5-9km

Density

2.7g/cm³

3.0g/cm³

Main rock type

Granite

Basalt

Materials

SIAL

SIMA

 The density of the crustal rocks is lower than the core and mantle because of lighter elements such as oxygen, silicon, aluminium, potassium and sodium. There is a large difference in the thickness of the crust depending on what is on the surface. It can range from only 5km thick below the oceans to up to 65km think below mountain ranges.

The theory of plate tectonics suggest of three more layers incorporating different parts of the Crust Mantle and Core.

Lithosphere

The Lithosphere is the crust and the rigid upper part of the mantle forming a layer which is 80km thick; this is divided in to 12 larger plates and numerous smaller ones

Asthenosphere

The asthenosphere is semi-molten material below the lithosphere on which the plates of the lithosphere ‘float’.  The asthenosphere is several hundred kilometres thick

Plate tectonic theory

The location of continents today of far removed from what it was millions of years ago, when it is believed that all continents were joined to one land mass, Pangaea, which later spilt into Laurasia in the north and Gondwanaland to the south. Alfred Wegener put forward a theory regards their movement in 1912 with his theory of Continental Drift. His theory was based on observations such as:

Biological and Geological:

·         Coal is found in UK but needs warm, wet, humid conditions to form.

·         Late-Carboniferous glaciations evidence exists in India, South America and Antarctica

·         Rock sequences in Northern Scotland match those in Eastern Canada

·         Mesosaurus fossils are found in Southern Africa and South America

Observational: The shapes of countries appear to 'fit' one another, for example, S. America and Africa.

In the 1940's-1960's the theory was revised and Plate Tectonic theory emerged, based on the premise that the lithosphere is divided into plates, which are…