MANTLE DYNAMICS:
A Deep Root for Iceland?
Richard A. Kerr
For decades, researchers have debated whether the plumes that feed the fires of long-lived volcanic centers around the globe rise from the bottom of Earth's lower mantle, 2900 kilometers down, or are rooted only a few hundred kilometers down in the upper mantle. The answer would determine whether the bulk of Earth's rocky mass is forever sealed off in the lower mantle or can mix into the upper mantle and so shape the surface. Now seismologists studying earthquake waves that probed the mantle deep below Iceland have detected signs of a narrow, hot plume at the traditional boundary between upper and lower mantle, about 660 kilometers down.