Scientists map deep origins of the 'Hawaiian Hotspot'

[n2doc]

Published: Thursday, December 3, 2009 - 17:32 in Earth & Climate

The Hawaiian Islands are one of the outstanding volcanic features on Earth, but their origins have been shrouded in mystery. Still in debate is a theory that was proposed forty years ago, which states that mid-plate hotspots such as Hawaii are generated by upwelling mantle plumes from the base of the lower mantle. Cecily Wolfe, a professor from the University of Hawai'i at Mānoa School of Ocean and Earth Science and Technology, and a multi-institutional team of scientists have put the theory to test. Their research findings, titled "Mantle Shear-wave Velocity Structure beneath the Hawaiian Hotspot," will be published in the December 4 edition of Science magazine.

A deployment of a large network of sea-floor seismometers in Hawai'i, called the Plume-Lithosphere Undersea Melt Experiment (PLUME), opened up a window into the Earth, obtaining the best picture yet of a mantle plume originating from the lower mantle and finally revealing Hawai'i's deep roots.

The seismometers were used to record the timing of seismic shear waves from large earthquakes (magnitudes greater than 5.5) around the world. This information can be used to determine whether seismic waves travel more slowly through hot rock as they pass beneath Hawai'i. Combining the timing measurements from many earthquakes recorded on many seismometers allowed Wolfe to construct a sophisticated 3-dimensional image of the Hawaiian mantle. The large, 1,000-km wide aperture of the seafloor network yielded unprecedented deep resolving power in a remote oceanic region, and inclusion of SKS waves (a type of wave that travels through the Earth's core) was critical for extending the imaging down to 1,500 kilometers depth.

The images from the PLUME experiment provide strong support for the existence of a mantle plume beneath Hawai'i. In the upper mantle, the Hawaiian Islands are underlain by low shear-wave velocities, consistent with hotter-than-average material from an upwelling plume. Low velocities continue down into the Earth's transition zone, at 410 to 660 km depth, and extend even deeper into the Earth's lower mantle down to at least 1,500 km depth. Strikingly, the plume tilts toward the southeast of Hawai'i as it extends downward. Such southeast tilting is consistent with prior dynamic predictions that the background circulation of the Earth's mantle associated with plate tectonics will deflect the upwelling Hawaiian plume. Or, in other words, like rising smoke on a windy day, the Hawaiian plume conduit is blown in the background mantle wind.

http://esciencenews.com/articles/2009/12/03/scientists.map.deep.origins.hawaiian.hotspot

[CaliforniaPeggy]

1. Plate tectonics has always fascinated me...

This is a terrific report.

K&R

[tabatha]

2. Yep, it is fun

to understand that serpentine outcrops originated from the bottom of the mantle. That is where the ultramafic rock layers with greater than 90% heavy mafic minerals (ma) for magnesium and (fi) for iron are found, and then brought up to the surface with plate tectonics/volcanic action. Ultramafic rocks metamorphize into green serpentinite, and eventually turn red as the iron in the rock oxidizes.

Then to find plants that have adapted to growing on serpentine rocks is cool, too - such as Serpentine Sunflower.

[Vinnie From Indy]

3. I have always found the phenomena of mega-tsunamis generated from Hawaii

It seems that the islands of Hawaii have been the source of mega-tsunamis generated when the older islands have at one time or another sloughed parts of themselves off into the sea.