Erica M. Mentone
Plate tectonics is the base for many natural disasters. The energy released from inside the earth can cause earthquakes and volcanic activity. Below our feet, there is a constant cycle of tectonic plate activity.
There are three layers within our earth: the Crust, on which we live; the mantle, just below the crust; and the core, at the center. The core is very dense and balanced on top of it is a less dense mantle. The mantle is about 2,900-km (1,800-mi) thick and made up of two parts, the Asthenosphere and the Lithosphere (Abbott, 2004). The Asthenosphere is deeper, weak, and ductile. The Lithosphere is settled atop the Asthenosphere and it is colder and stronger. The entire mantle is fluid. It is solid, but when exposed to pressure over a long period of time, it is able to flow and deform slowly because of its very high viscosity. The top layer of our planet is called the crust. It is hard and brittle.
The plates that make up the earth's crust and lithosphere are always moving and changing, and it is at the plates' boundaries where the most fierce disasters occur. The cooling mantle is the energy source for plate tectonics. The plates float on the viscous rock of the mantle until it becomes too heavy and begins to sink. Because the mantle is viscous and the crust is hard and brittle, when too much stress from the movement of the mantle is built up against the crust, it breaks causing earthquakes and volcanoes.
As they move, plates traveling in opposite directions rub against one another. The edges of the plates cause friction and this creates fairly large earthquakes. These are called transform faults. An example of this type of fault is the San Andreas Fault in California. Divergence zones are places where plates are moving away from each other. At these points there are often mild earthquakes, and volcanoes that occur where hot magma flows up through the weakened areas of crust in the spreading center. These types of faults are most often found at the ocean floor. In a subduction zone, there are two tectonic plates that are colliding. When one plate is colder and heavier than the other, the heavy plate begins to sink underneath the lighter plate and conforms back into the denser mantle. This causes much friction which can trigger the largest of all earthquakes.
When plates converge, it causes stress on the rock; the stress builds and builds until the stress can no longer be supported by the rock. That is the breaking point at which earthquakes occur. After the earthquake, plates continue their constant movement until they again meet a point of resistance where they start to build up stress again.
Over 80% of earth's volcanic activity occurs in spreading centers underwater. At these points, tectonic plates move apart and mama flows up to the surface where it is cooled by the ocean's waters. Subduction fault volcanoes do not erupt as often, but they are more violent. As a subducting plate is sinking into the earth's asthenosphere water and sediments remain on the plate. When the water lowers the melting point of the rock, it can be partially melted as it passes down towards the asthenosphere. Because of convection, plumes of magma rise up back towards the crust. When too much stress is built up against the rock, it causes an explosive volcanic eruption to release the pressure. After the eruption, the volcano may remain dormant for hundreds of years until enough stress is built up to cause another dangerous eruption Abbott, 2004).
