Lithospheric Processes & Hazards

Aso, Kyushu, Japan

The earth’s crust is divided into separate sections called tectonic plates. These plates are solid and float on semi-molten material in the Upper Mantle or Asthenosphere and are subjected to movement. It is this movement that causes earthquakes and volcanic eruptions to occur. The Asthenosphere is kept plastic (deformable) through heat generated by radio-active decay. The decaying material consists of radio-active isotopes of light elements such as Aluminum and Magnesium.

Due to this process convention cells develop – these are places where extremely hot magma rises to the upper portion of the mantle (Asthenosphere). The convection cells is the movement of cool liquid sinking and lower down being heated to then rise up again. This occurs because heated liquid is less dense than cool liquid. This rising and sinking occurs in a circular motion, the plates stick to the mantle due to friction causing them to move as the mantle moves.

The earth’s crust is divided into several tectonic plates, which constantly move. This is how energy is transferred from the center of the earth to the surface. Magma is only formed when pressure is released. The only areas around the world where pressure can be released are between tectonic plates; therefore volcanoes form where tectonic plates meet. When tectonic plates shift they create space for pressure to be release from the core of the earth to the crust creating an eruption.

Geologists have been able to determine what the internal structure of the earth looks like by studying wavelengths. When an earthquake occurs three different types of waves are formed, pressure, transverse and surface waves. These waves travel through solid and dense material very quickly. Observing the velocity of these waves result or determine the state of matter of the material, which they travel through. The study of these waves show that they reach a very high velocity at the most northern part of the earth where the crust and outer most part of the mantle is very solid and dense but further south towards the equator the waves slow down drastically and stop because they have reached the earth’s core. The reduction in the waves velocity strongly implies that waves have reached matter of a liquid state. Waves travel very slowing through liquids. These results aid geologists in gaining very accurate information about the internal structure of the earth.

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There are two main ways to classify a volcano, its shape and the nature of its eruption. The basaltic or acidic level of the lava determines the shape and nature of the explosion. Basaltic lava is very fluid and releases gradually therefore no explosive eruption. The level of viscousity in the rhyolitic lava is very dense and flows very slowly. Due to its density rhyolitic lava forms a volcanic plug in the vent of the volcano above the magma chamber and builds up pressure and eventually causes an extreme explosion. Mount Aso is located on the most southern island ...

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