In the not too distant past, cartographers charted
the deep ocean trenches, seismologists plotted
earthquakes beneath the trenches, and volcanologists
studied the overlying volcanoes. But these researchers
worked independently of each other, and were unaware
that the phenomena they studied were all part
of a singular process. Today, the ideas of sea-floor
spreading and subduction explain clearly why so
many of the worlds volcanoes are situated
on the Pacific island arcs, the Ring of Fire,
where earths tectonic plates are being subducted
beneath deep ocean trenches.
After about 10 million years, the final stage
of subduction begins. At depths of as much as
450 miles, the plate becomes so hot that it softens
and stops generating earthquakes. But the descent
and melting continue until, at some unknown depth,
the plate blends with the surrounding mantle material.
Eventually this material will emerge along Mid-Ocean
Ridges as new sea-floor crust or escape as volcanic
lava as the process of subduction comes full circle
and our tectonic planet continues to evolve.