December 11, 2000
Contacts: Shelley Lauzon, Woods
Hole Oceanographic Institution 508/289-2270
Mario Aguilera, Scripps Institution of Oceanography 858/534-3624
Color maps and a perspective
view of the volcano are available at: http://184.108.40.206/publicationsfinal/articles/2000GC000108/fs2000GC000108.html
Activity Discovered at Samoan "Hot Spot"
Underwater volcanic explosions
could produce danger as a major navigational hazard
Scientists from Woods Hole
Oceanographic Institution and Scripps Institution of Oceanography have
discovered "strong evidence" for current volcanic activity at
the Vailulu’u summit east of Samoa.
In the electronic journal Geochemistry,
Geophysics and Geosystems, Stan Hart of Woods Hole and Hubert
Staudigel of Scripps Institution report that Vailulu’u’s crater is
filled with smoggy waters, more turbid than any other underwater volcano
They analyzed the distribution
of particulate matter, or underwater "smog," that forms when
hot volcanic rocks react with seawater. This smog spills over the crater
rim and forms a halo around the Vailulu’u summit. These reactions
produce particulates, including minerals formed from the reactions
between seawater and volcanic rock, and from elevated levels of
biological activity that is characteristic of most submarine eruptions
and hydrothermal systems.
"The discovery of a ‘smoking’
active underwater volcano at the eastern end of the Samoan Island chain
is significant because it supports the interpretation of the Samoan
islands as a hot spot chain, similar to Hawaii," said Hart .
"It also provides a unique natural laboratory where submarine
volcanism and its physical, biological, and chemical effects may be
studied in close proximity to an island."
Locating a new hot spot volcano
such as Vailulu’u provides fundamental insights into how ocean island
chains form and is important for determining the absolute motion of the
But such underwater volcanoes
also may be dangerous, the authors said. "Submarine volcanoes like
Vailulu’u are potentially hazardous because a 600-meter-deep
underwater volcano may become highly explosive during underwater
eruptions," said Staudigel. "Such underwater explosions are
dangerous because the volcanic explosive strength can be highly
amplified by the force of the vaporization of seawater. This may cause
tidal waves and could present a major navigational hazard."
The report is the result of two
expeditions aboard the Scripps research vessel Melville and the
U.S. Coast Guard ice breaker Polar Star.
Vailulu’u is located at the
eastern leading edge of the Samoan ridge and rises from 5,000 meters to
within about 600 meters of the sea surface, including a
2-kilometer-wide summit crater. Three rift zones extend from this crater
to the east, west, and southwest, very closely resembling the physical
appearance of Ta’u, the neighboring island to the west. Vailulu’u is
similar in size to many well known volcanoes, such as Mt. Fuji in Japan
and Mt. Rainier in Washington State.
Rocks dredged by the scientists
from Vailulu’u had shiny fresh glassy surfaces and a sulphurous odor
that are characteristic of very recently erupted undersea lavas.
The timing of Vailulu’u’s
volcanic activity is close to events that have been recorded by global
seismic networks. Major earthquake activity was recorded at or near
Vailulu’u in July 1973 and January 1995. The authors say it is quite
possible that these two seismic swarms were related to the eruptions
that produced their dated rock samples.
Using isotopic tracing
techniques, the scientists determined that the volcano was formed by
partial melting of materials in the earth’s mantle with a
characteristically "Samoan" composition or pedigree. The
examinations suggested volcanic activity within the past 5 to 50 years,
further evidence that Vailulu’u is the current location of the Samoan
As an interesting sidelight,
the evidence for volcanic activity at Vailulu’u may have an historical
antecedent in Samoan mythology. Kanaloa, the oldest Polynesian volcano
god, is said to have been involved in a violent battle to the East of Ta’u
after which he landed on its eastern slopes. The site of his landing was
honored with a temple to Kanaloa, built about 3,000 years ago. This
temple faces the site of Kanaloa’s battle, and current location of
Vailulu’u. Perhaps the ancient Polynesians knew about Vailulu’u all
In March 2000, the scientists
deployed ocean bottom seismographs on the summit of Vailulu’u to
listen to microseismic activity that will produce data to provide
further clues to the presence of volcanic activity and help determine
when and where magma moves within the volcano.
The deployment of seismographs
included one deployment by helicopter – a method of marine instrument
deployment that has never been done before, which may prove very useful
in the quick response to a submarine volcanic crisis.
The research cruises were
funded by the National Science Foundation.
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