GEOLOGY ASSIGNMENT BY DANNY HAMPTON

Subduction Subduction in the geological manner is the process that takes place as the boundaries of the Tectonic Plates. It is when one tectonic plate moves under another, sinking into the earths mantle. Subduction Zones are often noted for their high rates of volcanic and earthquake activity, also their mountain building. DIAGRAM OF SUBDUCTION

Earthquakes Earthquakes Are usually caused when a rock along a fault breaks. There is a sudden release of pressure which causes seismic waves that make the ground shake. When two blocks of rock or two tectonic plates are rubbing together they stick a little. They don't just slide smoothly; the rocks catch on each other. The rocks are still pushing against each other, but not moving. After a while, the rocks break because of all the pressure that's built up. When the rocks break, the earthquake occurs.

Structure of the Earth The earth is made up of 4 main layers; Crust, Mantle, Outer Core, and Inner Core.

P Waves P-waves are a type of elastic wave, also called seismic waves, that can travel through gases as sound waves, solids and liquids, including the Earth. P-waves are produced by earthquakes and recorded by seismographs. The name P-wave is often said to stand either for primary wave, as it has the highest velocity and is therefore the first to be recorded; or pressure wave, as it is formed from alternating compressions and rarefactions.

Mantle Convection Mantle convection is the slow creeping motion of Earth's rocky mantle caused by convection currents carrying heat from the interior of the Earth to the surface. The Earth's surface lithosphere, which rides atop the asthenosphere, the two components of the upper mantle, is divided into a number of plates that are continuously being created and consumed at their opposite plate boundaries. Accretion occurs as mantle is added to the growing edges of a plate, usually associated with seafloor spreading. This hot added material cools down by conduction and convection of heat. At the consumption edges of the plate, the material has thermally contracted to become dense, and it sinks under its own weight in the process of subduction at an ocean trench.

Theory of Earths History According to the theory of continental drift, the world was made up of a single continent through most of geologic time. That continent eventually separated and drifted apart, forming into the seven continents we have today. The first comprehensive theory of continental drift was suggested by the German meteorologist Alfred Wegener in The hypothesis asserts that the continents consist of lighter rocks that rest on heavier crustal material, similar to the manner in which icebergs float on water. Wegener contended that the relative positions of the continents are not rigidly fixed but are slowly moving, at a rate of about one yard per century. According to the generally accepted plate-tectonics theory, scientists believe that Earth's surface is broken into a number of shifting slabs or plates, which average about 50 miles in thickness. These plates move relative to one another above a hotter, deeper, more mobile zone at average rates as great as a few inches per year. Most of the world's active volcanoes are located along or near the boundaries between shifting plates and are called plate-boundary volcanoes.