A spider crab inspects an ocean-bottom hydrophone mooring at the Axial Seamount before its 2011 eruption. The hydrophone, in the white pressure case, is designed to detect undersea earthquakes. Photo: Bill Chadwick, Oregon State University, copyright Woods Hole Oceanographic Institution
team of scientists just discovered a new eruption of Axial Seamount, an
undersea volcano located about 250 miles off the Oregon coast—and one
of the most active and intensely studied seamounts in the world.
makes the event so intriguing is that the scientists had forecast the
eruption starting five years ago – the first successful forecast of an
Chadwick, an Oregon State University geologist, and Scott Nooner, of
Columbia University, have been monitoring Axial Seamount for more than a
decade, and in 2006 published a paper in the Journal of Volcanology and
Geothermal Research in which they forecast that Axial would erupt
before the year 2014. Their forecast was based on a series of seafloor
pressure measurements that indicated the volcano was inflating.
are notoriously difficult to forecast and much less is known about
undersea volcanoes than those on land, so the ability to monitor Axial
Seamount, and determine that it was on a path toward an impending
eruption is pretty exciting,” said Chadwick, who was chief scientist on
the recent expedition, which was jointly funded by the National Oceanic
and Atmospheric Administration and the National Science Foundation.
last erupted in 1998 and Chadwick, Nooner and colleagues have monitored
it ever since. They used precise bottom pressure sensors—the same
instruments used to detect tsunamis in the deep ocean—to measure
vertical movements of the floor of the caldera much like scientists
would use GPS on land to measure movements of the ground. They
discovered that the volcano was gradually inflating at the rate of 15
centimeters (six inches) a year, indicating that magma was rising and
accumulating under the volcano summit.
Axial erupted in 1998, the floor of the caldera suddenly subsided or
deflated by 3.2 meters (10.5 feet) as magma was removed from underground
to erupt at the surface. The scientists estimated that the volcano
would be ready to erupt again when re-inflation pushed the caldera floor
back up to its 1998 level.
the eruption of most land volcanoes is normally very difficult at best
and the behavior of most is complex and variable,” said Nooner, who is
affiliated with the Lamont-Doherty Earth Observatory. “We now have
evidence, however, that Axial Seamount behaves in a more predictable way
than many other volcanoes—likely due to its robust magma supply coupled
with its thin crust, and its location on a mid-ocean ridge spreading
is now the only volcano on the seafloor whose surface deformation has
been continuously monitored throughout an entire eruption cycle,” Nooner
discovery of the new eruption came on July 28, when Chadwick, Nooner
and University of Washington colleagues Dave Butterfield and Marvin
Lilley led an expedition to Axial aboard the R/V Atlantis, operated by
the Woods Hole Oceanographic Institution. Using Jason, a remotely
operated robotic vehicle (ROV), they discovered a new lava flow on the
seafloor that was not present a year ago.
The chain is all that is visible of an ocean-bottom hydrophone buried in about six feet of new lava from an April 2011 eruption of Axial Seamount. Photo: Bill Chadwick, Oregon State University; copyright Woods Hole Oceanographic Institution
funny,” Chadwick said. “When we first arrived on the seafloor, we
thought we were in the wrong place because it looked so completely
different. We couldn’t find our markers or monitoring instruments or
other distinctive features on the bottom. Once we figured out that an
eruption had happened, we were pretty excited.
eruptions like this occur, a huge amount of heat comes out of the
seafloor, the chemistry of seafloor hot springs is changed, and
pre-existing vent biological communities are destroyed and new ones
form,” Chadwick added. “Some species are only found right after
eruptions, so it is a unique opportunity to study them.”
first Jason ROV dive of the expedition targeted a field of “black
smoker” hot springs on the western side of the caldera, beyond the reach
of the new lava flows. Butterfield has been tracking the chemistry and
microbiology of hot springs around the caldera since the 1998 eruption.
hot springs on the west side did not appear to be significantly
disturbed, but the seawater within the caldera was much murkier than
usual,” Butterfield said, “and that meant something unusual was
happening. When we saw the ‘Snowblower’ vents blasting out huge volumes
of white floc and cloudy water on the next ROV dive, it was clear that
the after-effects of the eruption were still going strong. This
increased output seems to be associated with cooling of the lava flows
and may last for a few months or up to a year.”
scientists will examine the chemistry of the vent water and work with
Julie Huber of the Marine Biological Laboratory to analyze DNA and RNA
of the microbes in the samples.
scientists recovered seafloor instruments, including two bottom
pressure recorders and two ocean-bottom hydrophones, which showed that
the eruption took place on April 6 of this year. A third hydrophone was
found buried in the new lava flows.
far, it is hard to tell the full scope of the eruption because we
discovered it near the end of the expedition,” said Chadwick, who works
out of OSU’s Hatfield Marine Science Center in Newport. “But it looks
like it might be at least three times bigger than the 1998 eruption.”
The lava flow from the 2011 eruptions was at least two kilometers (1.2 miles) wide, the scientists noted.
years ago, these scientists forecast this eruption, which has resulted
in millions of square meters of new lava flows on the seafloor,” said
Barbara Ransom, program director in the National Science Foundation’s
Division of Ocean Sciences. “The technological advances that allow this
research to happen will lead to a new understanding of submarine
volcanoes, and of any related hazards.”
bottom-anchored instruments documented hundreds of tiny earthquakes
during the volcanic eruption, but land-based seismic monitors and the
Sound Surveillance System (SOSUS) hydrophone array operated by the U.S.
Navy only detected a handful of them on the day of the eruption because
many components of the hydrophone system are offline.
the earthquakes detected back in April at a distance from the volcano
were so few and relatively small, we did not believe there was an
eruption,” said Bob Dziak, an OSU marine geologist who monitors the
SOSUS array. “That is why discovering the eruption at sea last week was
such a surprise.” Both Dziak and Chadwick are affiliated with the
Cooperative Institute for Marine Resource Studies – a joint NOAA/Oregon
State University institute.
latest Axial eruption caused the caldera floor to subside by more than
two meters (six feet). The scientists will be measuring the rate of
magma inflation over the next few years to see if they can successfully
forecast the next event.
acid test in science—whether or not you understand a process in
nature—is to try to predict what will happen based on your
observations,” Chadwick said. “We have done this and it is extremely
satisfying that we were successful. Now we can build on that knowledge
and look to apply it to other undersea volcanoes—and perhaps even
volcanoes on land.”
OSU’s Hatfield Marine Science Center: The center is a research and
teaching facility located in Newport, Ore., on the Yaquina Bay estuary,
about one mile from the open waters of the Pacific Ocean. It plays an
integral role in programs of marine and estuarine research and
instruction, as a laboratory serving resident scientists, as a base for
far-ranging oceanographic studies and as a classroom for students.