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A 'Book' of Ancient Sumatran Tsunamis Historic Chinese cruise brings back clues to old earthquakes and new vent sites |
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| Enlarge ImageJian Lin (yellow hard hat), a geophysicist at Woods Hole Oceanographic Institution, was U.S. chief scientist aboard two voyages of China's new research vessel in 2005—the first American ever invited to co-lead a Chinese deep-ocean research cruise. He and Professor John Chen of Peking University deploy a Miniature Autonomous Plume Recorder to search for hydrothermal vents. (Photo by Mingyu Mi, China Central Television) |
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| Enlarge ImageWHOI scientist Jian Lin (right) looks at a sediment core just retrieved from the site of the seafloor earthquake off Sumatra that caused the 2004 Indian Ocean tsunami. Lin hopes the core contains a record of past tsunamis. (Photo by DayangYiHao, science party) |
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| Enlarge ImageLin will analyze the sediment cores he retrieved from the seafloor off Sumatra to see if it can reveal a history of earthquakes and tsunamis in the region. (Photo by Tom Kleindinst, Woods Hole Oceanographic Institution) |
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| Enlarge ImageOne year after the 2004 tsunami, with their research vessel above the site of the submarine earthquake that spawned it, Lin and the entire ship's crew participated in a solemn ceremony to commemorate the tsunami’s victims, casting origami cranes and flowers into the waves. (Photo by Hongjie Qiu, Xinhua News Agency) |
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Exactly one year after the devastating 2004 Indian Ocean tsunami, Jian
Lin found himself on a Chinese research vessel off Sumatra, floating
above the epicenter of the seafloor earthquake that spawned the great
wave.
He participated in a solemn ceremony to honor the estimated 280,000
people killed by the tsunami. Then he hauled up cores of ancient
sediment from the ocean bottom—cores that could reveal the history of
tsunamis, help predict their likelihood, and perhaps save lives in the
future.
“You are looking at a book,” said Lin, a geophysicist, pointing to a
1½-meter-long column of mud in his office at Woods Hole Oceanographic
Institution. “Now we must learn to read the pages and hope it contains
chapters that will teach us how—and how frequently—earthquakes create
tsunamis in this region.”
The tantalizing sediment samples culminated two 40-day voyages for Lin
as U.S. chief scientist aboard China’s new research ship, Dayang 1. It
was the first time an American scientist has been invited to co-lead a
Chinese deep-ocean research cruise (see Worlds Apart, But United by the Oceans).
'Sniffing' to find new seafloor vent sites
During 2005, Dayang 1 sailed an ambitious 300-day series of expeditions
to explore mineral and biological resources in the ocean, particularly
at hydrothermal vents. To this unique collaboration, Lin brought
seafloor maps from previous WHOI expeditions and a WHOI-built deep-tow
magnetometer to detect mineral-rich ocean crust around vents. He also
brought six Miniature Autonomous Plume Recorders (MAPRs), on loan from
Edward Baker, Lin’s colleague at the National Oceanic and Atmospheric
Administration.
Lin described MAPRs as “sniffers.” Lowered on wires into the depths,
they detect hot, buoyant, particle-filled fluids emitted from seafloor
vents. The fluids rise several hundred meters above the seafloor and
spread sideways into mushroom-shaped plumes above the vent “stems.”
MAPRs measure temperature, as well as the scattering of light (by
dissolved particles) through seawater.
With these and other tools at their disposal, the international team
aboard Dayang 1 discovered new regions of strong hydrothermal plumes in
the eastern Pacific Ocean and atop of the Southwest Indian Ridge
(SWIR). They also recovered microorganisms that live under extreme
conditions in the deep ocean and many samples of sulfide rocks from
hydrothermal vents. These represented firsts for China. By flying the
magnetometer on an underwater vehicle only tens of meters above the
seafloor, Lin and colleagues measured Earth’s magnetic field at very
close range to determine the magnetic properties of unusual rocks found
on the ultra-slow-spreading SWIR.
“The Indian Ocean cruise was probably the most fruitful expedition I
have ever co-led,” Lin said. On a little-explored region of the SWIR,
the MAPRs found a extremely robust hydrothermal plume, though the team
did not have time to follow the plume trail to the vents that created
it.
“This vent site is just waiting to be confirmed,” Lin said, “and
scientists are now actively planning to go back as soon as possible. It
would be the first large active vent ever found on the Southwest Indian
Ridge and would fill in a missing geological and biological piece in
the seafloor jigsaw puzzle.”
One year later, an unsettled ocean
In December 2005, Dayang 1 headed east toward Indonesia. Near the
tsunami-generating earthquake site off Sumatra, the MAPRs found a
surprise: One year after the tsunami, the bottom 2,000 feet (600
meters) of the ocean were still murky and filled with particles.
“Major seafloor earthquakes and tsunamis send huge amounts of seafloor
sediments whirling into the ocean,” Lin said. “Our hypothesis was that
big sediment grains would settle first, then medium grains, then fine
grains, and then very fine grains.”
Stirred and sorted by tsunamis, the resettled fine-grained particles
could leave telltale layers in sediments. “If we can find these layers
in the cores I brought back, correlate them with previous known quakes,
and date others deeper down in the cores,” Lin said, “then we may
actually be able to read the history of earthquakes and tsunamis in
this region.”
During a moment of silence in the tsunami memorial ceremony on Dayang
1, with everyone lined up on deck, “I thought about the immeasurable
suffering of those affected by the tsunami,” Lin said, “and an enduring
need to better understand and eventually forecast earthquakes and
tsunamis.”
Then the ship’s horn blew for a full minute, and the ship’s party sank
an inscribed concrete memorial to the tsunami victims into the sea.
They cast origami cranes and flowers into the waves, as well as paper
money, a Chinese tradition to pay respect to those in heaven.
—Lonny Lippsett
Lin’s research was funded by the U.S. Office of Foreign Disaster Assistance and a WHOI Independent Study Award.
Posted: May 15, 2006 [top] |
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