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Twin peaks reveal what lies beneath
By Alexandra Witze
Hawaii’s scenic volcanoes come in two
chemical flavors, and now scientists
think the igneous peaks on other Pacific
island chains do, too.
Two parallel lines of volcanoes
stretch from the Big Island of Hawaii in
the southeast to Molokai in the north-west. Volcanoes on the Samoan and
Marquesas islands are similarly paired.
A new study finds that in all three chains
one row of volcanoes is richer than the
other in versions of elements such as
lead and neodymium.
“This might be a common feature for
all the Pacific hot spots,” says Shichun
Huang, a geochemist at Harvard and
lead author of a paper appearing online
September 18 in Nature Geoscience.
If so, these island chains may tap
similar sources deep in Earth’s mantle.
Molten rock rises toward the surface in
two chemically distinct streams, one
stream feeding each row of volcanoes.
Geologists think Hawaii, Samoa and
the Marquesas each formed as a plate of
Earth’s crust moved across a “hot spot,”
the top of a plume carrying molten mate-
rial from the planet’s deep interior. Like
a welding torch passing across a piece of
metal, the hot spot punched out island
after island as the plate moved over it.
Studies suggest that the molten rock
forming the volcanoes on Hawaii and
other Pacific island chains derives from
a geochemically varied source.
of this material with it.
The new work shows how surface volcanoes can be linked to deep sources
of magma, says geochemist Albrecht
Hofmann of the Max Planck Institute
for Chemistry in Mainz, Germany. A
few other scientists have questioned
the existence of mantle plumes, but
the new work “strongly suggests that at
least these particular hot spots are actually mantle plumes that ascend from the
lowermost mantle,” Hofmann says. s
Nature’s crystal palace
Mexico’s Cueva de los Cristales, or Cave of Crystals, may look
like Superman’s Fortress of Solitude. But unlike its comic
book counterpart, this cave’s assortment of supersized crystals took a lot longer than a few minutes to grow.
Under a laboratory microscope, pieces of these gypsum
crystals immersed in mineral-rich water elongated a mere billionth of a meter per day—the slowest ever measured in a
crystal —a team of scientists in Spain and Japan reports in
the Sept. 20 Proceedings of the National Academy of Sciences.
Depending on temperature, the crystals could have reached
their modern-day lengths, up to 11 meters, in 100,000 to
1 million years.
To nurture such growth, cave temperatures must have
ranged from about 50° to 58° Celsius, the team reports. While
no fortress, this balmy lair — with its icelike decor — might
have made a nice sauna for the Man of Steel. — Devin Powell
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