G) The basic theory is that the surface layer of the earththe lithosphereis comprised of many plates that slide over the lubricating asthenosphere layer. At the boundaries between these huge plates of soil and rock, three different things can happen.
H) Plates can move apart. If two plates are moving apart from each other, hot, molten rock flows up from the layers of mantle below the lithosphere. This magma comes out on the surface , where it is called lava .As the lava cools, it hardens to form new lithosphere material, filling in the gap. This is called a divergent plate boundary.
I) Plates can push together. If the two plates are moving toward each other, one plate typically pushes under the other one. This plate below sinks into the lower mantle layers, where it melts. At some boundaries where two plates meet, neither plate is in a position to push under the other, so they both push against each other to form mountains. The lines where plates push toward each other are called convergent plate boundaries.
J) Plates slide against each other. At other boundaries, plates simply slide by each otherone moves north and one moves south, for example. While the plates dont drift directly into each other at these transform boundaries, they are pushed tightly together. A great deal of tension builds at the boundary.
K) We understand earthquakes a lot better than we did even 50 years ago, but we still cant do much about them. They are caused by fundamental, powerful geological processes that are far beyond our control. These processes are also fairly unpredictable, so its not possible at this time to tell people exactly when an earthquake is going to occur. The first detected earthquake waves will tell us that more powerful vibrations are on their way, but this only gives us a few minutes warning, at most.
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