Basic Geology/Plate Tectonics
Plate Tectonics is a theory that almost all of the world's scientists believe is true. It involves tectonic plates: puzzle-like formations under the Earth's crust that are floating on a layer of magma called the mantle. The mantle is a layer of the earth. The crust is another, it is what we live on. Tectonic plates are part of a layer called the lithosphere. The lithosphere floats on a section of the upper mantle called the asthenosphere. The asthenosphere is a place where hot magma swirls in a convection current. This current causes the movement of the tectonic plates.
Tectonic plates are constantly moving around, colliding, and drifting apart. The edges where two plates meet is called a "plate boundary". Sometimes plates move apart from one another; this is called divergence. Sometimes plates move toward one another; this is called convergence. Convergence can cause one plate to slide underneath the other; this is called subduction. A transform plate boundary is when the edges of two plates don't converge or diverge, but slide alongside each other.
When plates converge, diverge or slide past each other, it can cause earthquakes and tsunamis. Additionally, most volcanoes are formed at or near plate boundaries. Some volcanoes are formed at divergent plate boundaries. This is because when two plates part, it allows the mantle beneath them to melt into magma, which then rises between the plates to form volcanoes. The island of Iceland was formed in this manner. Other volcanoes are found at or near subduction zones, where an oceanic plate is forced underneath either a continental plate or another oceanic plate. The top of the subducting plate contains a significant amount of surface water, as well as water contained in hydrated minerals within the seafloor basalt. As the subducting plate descends to greater and greater depths, it encounters higher temperatures and greater pressures which cause the plate to release the water into the mantle wedge above it. This water has the effect of lowering the melting temperature of the mantle, thus causing it to melt. The melted mantle, called magma, then rises upward to produce a series of volcanoes. The Cascade volcanoes in North America, and the volcanoes of the Lesser Antilles, are two examples of this. However, a few volcanoes are formed far from plate boundaries. These volcanoes are formed above hot spots in the mantle, and are called "hot spot volcanoes". The Hawaiian islands, for example, were formed in this way.