This includes not only the size of the plates but also the geometry of plate boundaries and even the stability of so-called hot spots that underlie island arcs such as the Hawaiian Islands. Because convection in the mantle is assumed to nudge the continents around on the surface of the Earth and break them up into plates of roughly the same size as the convection cell, this model provides an explanation for why the plates are the size they are. Geophysicist Mark Richards and graduate student Hans-Peter Bunge describe the model in a cover article scheduled for publication in the October issue of Geophysical Research Letters. The effect has only recently been established from seismic studies. Instead of isolated point-like cold blobs dropping into the interior, the pattern changes to long, linear structures sliding into the interior that look like subduction zones.
Subduction zones are places where tectonic plates dive under one another into the mantle.
Their model also explains the stability of Earth's hotspots, upwellings of hot molten rock that remain constant for billions of years. The Hawaiian and Reunion Islands, as well as Yellowstone and Iceland, are examples of hot spots that have remained in the same place for much of the Earth's history. The reason, Richards says, is that these upwellings are rooted solidly in the very viscous deep mantle, near where it borders the core, and can't move.