Colloquium: William Sager

Not long ago it was widely accepted that rising currents of magma from deep in the Earth (mantle plumes) erupted chains of seamounts on the drifting plates at the surface. These melting spots have been called "hotspots".  What's more, it was thought that the plumes were nearly vertical and that they were fixed in the mantle, so geologists could track the motions of surface places from the seamount chains left behind.  Over time, the number of purported hotspots increased greatly and the hotspot theory expanded to include the "plume head" hypothesis, in which oceanic plateaus (huge undersea volcanic mountain ranges) were formed by a huge blob of magma created when a new plume was born.  In recent years, scientists have taken a hard look at the hotspot and plume head hypotheses and views on this basic tenet have shifted dramatically. Dr. Sager will take the listener along for a personal journey from once knowing what hotspots were all about towards a new understanding.  He will discuss the Hawaiian-Emperor seamount chain and how Pacific paleomagnetic data show that most textbooks interpret its formation wrongly and as well as how the hotspot behaved in a most un-plume-like manner.  He will also discuss recent drilling results from Shatsky Rise, an oceanic plateau and former "supervolcano", and how it could have erupted from a plume head - or not.

William Sager, Ocean Leadership Distinguished Lecturer