Can someone give me a brief introduction to livejournal?

Can someone give me a basic yet informative introduction on the plate tectonic theory?

• Just the basic things, no need to get into the details. For example I want to know why do these plates move, what cause earthquakes and volcano eruptions, why magma moves around, what's seafloor spreading and subduction. Thank you sooooooo much!!!

• Answer:

  The Earth's crust is broken up into tectonic plates which move slowly across the mantle in different directions. They interact at plate boundaries, causing earthquakes and volcanoes. The cause of plate movement isn't definitely established. Some believe that mantle plumes, plumes of material from deep in the mantle, that rises by convection and spreads out. Others believe that subduction pulls on the subducting plate, causing it to move. "There are four types of plate boundaries: Divergent boundaries -- where new crust is generated as the plates pull away from each other. Convergent boundaries -- where crust is destroyed as one plate dives under another. Transform boundaries -- where crust is neither produced nor destroyed as the plates slide horizontally past each other. Plate boundary zones -- broad belts in which boundaries are not well defined and the effects of plate interaction are unclear." Seafloor spreading is where the plates are moving away from one another (divergent boundary) under the sea. This occurs at the mid ocean ridge. The Mid Atlantic Ridge is the portion of this range at the boundary between the North American and Eurasian plates. Subduction occurs at convergent boundaries where the heavier (oceanic) plate is subducted beneath the lighter continental plate where the two push together. The movement of the plates at these boundaries cause earthquakes. Since rocks and dirt don't slide against each other very smoothly, the plate edges catch and pressure builds up until it overcomes the stoppage and releases, and a quake results. "Subduction processes in oceanic-oceanic plate convergence also result in the formation of volcanoes. Over millions of years, the erupted lava and volcanic debris pile up on the ocean floor until a submarine volcano rises above sea level to form an island volcano. Such volcanoes are typically strung out in chains called island arcs." Earthquakes also occur at transform boundaries by the same catch and release mechanism previously described. The San Andreas fault is an example of this. Volcanoes and some earthquakes also occur at divergent boundaries. Magma wells up in the space between the plate edges. This is how the Mid Atlantic Ridge, including the island of Iceland, was built. Volcanoes also occur at hot spots within tectonic plates. The Hawaiian Islands are an example of this. The Pacific plate moves toward the northwest. As the plate moves across the hot spot, the magma connection to the older volcanoes is broken and a new seamount begins as the magma finds its way to the surface at a new spot. The volcanoes on the oldest islands (the northwestern part of the chain) are extinct. A new seamount, Loihi, has formed off the coast southeast of the big island, which still has active volcanoes. As the plate continues to move and Loihi continues to build, it will become the newest island in the chain, and the volcanoes on the Island of Hawaii will become extinct.