For four decades, scientists have debated the theory that mid-plate hotspots such as Hawaiʻi are generated by mantle plumes upwelling from the base of the lower mantle near Earth’s core.
University of Hawaiʻi at Mānoa Associate Professor Cecily Wolfe of the Hawaiʻi Institute of Geophysics & Planetology and a team of researchers from Scripps, Woods Hole and Carnegie institutions put the theory to test.
Ten years in the planning, the Plume-Lithosphere Undersea Melt Experiment, or PLUME, deployed a large network of seismometers at 73 sea-floor sites in Hawaiʻi. Additional seismometers were placed on land. For two years, the seismometers recorded the timing of seismic shear waves from large earthquakes (magnitudes greater than 5.5) around the world.
Combining timing measurements from many earthquakes on multiple sensors allowed Wolfe to construct a sophisticated, 3-dimensional image 1,000 kilometers wide and 1,500 kilometers deep. Seismic shear waves travel more slowly through hot rock. The low velocities detected deep into Earth’s lower mantle jibe with the theorized plume.
The mantle plume tilts toward the southeast as it extends downward—consistent with predictions that the background circulation of Earth’s mantle associated with plate tectonics would deflect the upwelling Hawaiian plume much as rising smoke is carried on a windy day.
“The success of such an ambitious seafloor experiment is a technological feat in itself and signals a new era in the field of marine seismology,” says Wolfe. The results not only shed light on the geologic origin of Hawaiʻi, but provide clues to composition, convection process and evolution of the planet as well.
The results were published in the Dec. 4, 2009 issue of the journal Science. Read the abstract.