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| Early morning moon setting over Moana Kea (with the UCSC Keck Observatory visible at the right) in Hilo, Hawaii |
Seeing the full moon set over Moana Kea as we sailed into
Hilo, Hawaii, was not only a welcome sight after 7 days at sea, but was also a
reminder that these islands are all volcanic, created over five or six million
years as the massive Pacific Plate has moved northwest at a few inches a year
over a hot spot or thermal plume rising from deep within the Earth. Six million
years ago Kauai sat over the hot spot and was actively erupting, building that
island up nearly 30,000 feet from the seafloor. Each island gradually formed
and then died in a progression to the southeast as it moved away from the hot
spot or plume. Kauai, Oahu, Molokai, and Maui each had their day, and now
Hawaii sits over the plume, with Kilauea the most active volcano on Earth
directly connected to a source of magma deep in the mantle.
While many of the people on the ship expected a classic
steep-sided cone like Fujiyama, Mt. Saint Helens, or Shasta, the Hawaiian
volcanoes are all much more subdued, being shield volcanoes, or shaped like a
Roman shield resting on the ground. The difference in their shapes lies in the
nature of their eruptions, which results from different lava compositions. The
Hawaiian Islands consist entirely of basalt, lava low in silica. As a result
the eruptions produce very fluid lavas, which flow considerable distances at
only moderate speeds and are generally not a hazard to people- unless the
people are moving very slowly or in the wrong place at the wrong time
The Cascade volcanoes, on the other hand, as well as Mt.
Fuji, which loomed on the horizon on Yokohama as we sailed in early on the 29th
of January, have a classic steep-sided, symmetrical shape. The Chain of Fire,
or the volcanoes that surround the entire Pacific Ocean, contain a higher
silica content, and produce sticky, explosive eruptions, which build up steep,
cone shaped peaks. Our best view of Mt. Fuji came on our entry to Japan and as
the weather changed, we sadly never saw it again. But Deepika did get some nice
pictures (stay tuned...)
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| Kilauea steaming (photo by G. Griggs) |
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| Hiking across Kilauea Iki crater (photo by G. Griggs) |
I did lead a class field trip to Kilauea on a hike down
into and across Kilauea Iki, which was a red-hot, molten lava lake in the not
too distant past, and which is still releasing sulfur oxide fumes and hot
steam. As the lava lake gradually cooled and hardened the surface subsided and
left a surface looking an asphalt highway broken and cracked by an earthquake.
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| Site of 1959 Kilauea Iki 2000ft high eruption (photo by G. Griggs) |
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| Kilauea Iki following the lava lake cooling and collapse (photo by G. Griggs) |
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| Broken and collapsed lava from former molten lava lake (photo by G. Griggs) |
Walking across the now hardened lava brought thoughts of
walking over hot coals and led us to wonder when the next eruption was likely
to occur. Kilauea is monitored virtually
continuously by the U.S. Geological Survey’s Hawaiian Volcano Observatory,
through a combination of the earthquake detection beneath the volcano, GPS
measurements of the slopes around the volcano to see if there is any swelling,
as well as daily sampling of the gases being discharged for any changes.
Fortunately, the eruptions of Kilauea are somewhat more predictable and less
devastating than the volcanoes surrounding the Pacific Basin.
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Lava Tree - molten lava rushed around a living tree trunk, and immediately cooled, creating a mold of the tree within
(photo by G. Griggs) |
