OREGON STATE UNIVERSITY

MONITOR SURVIVES BLAST, GIVES FIRST LOOK AT SUBMARINE ERUPTION

08/15/2001

NEWPORT, Ore. - Information from an undersea monitor engulfed in lava during a deep ocean volcanic blowout is giving scientists their first-ever detailed view of an undersea eruption.

Researchers from Oregon State University and the National Oceanic and Atmospheric Administration are publishing results obtained from the volcanic system monitor data on Thursday in the journal Nature. The team is based at OSU's Mark O. Hatfield Marine Science Center in Newport.

The paper, "Direct Observation of a Submarine Volcanic Eruption from a Sea-floor Instrument Caught in a Lava Flow," was written by Christopher G. Fox, an OSU associate professor of oceanic and atmospheric sciences and part of NOAA's Pacific Marine Environmental Laboratory, volcanologist William W. Chadwick Jr. of OSU's Cooperative Institute for Marine Resources Studies, and Robert W. Embley, a marine geologist from the NOAA Vents Program and a professor of oceanic and atmospheric sciences. Fox is principal investigator for the study.

The paper describes in detail the results obtained from the NOAA device during an active eruption in 1998. The site of the eruption was Axial volcano, along the Juan de Fuca Ridge seafloor spreading center, located about 300 miles offshore from Cannon Beach, Ore. This volcano has been the focus of a long-term NOAA research effort, called the Vents Program, that seeks to understand the mechanisms by which the earth's interior exchanges heat and chemicals with the earth's surface through seafloor spreading centers.

The site was selected for study because geological evidence indicated Axial volcano to be potentially one of the most active in the deep sea and is also located near enough to the West Coast to be accessible by oceanographic vessels.

"We began monitoring Axial in 1987, using simple bottom pressure recorders to measure the long-term vertical movements of the seafloor associated with magma transport within the volcano," Fox said. "We never expected to get this close a look at the eruptive process."

Previously, vertical motions were detected by Fox's instruments and interpreted to represent magma movements, but not until 1998 did an actual eruption occur to confirm this hypothesis.

NOAA scientists acoustically detected the 1998 eruption through their access to the Navy's SOund SUrveillance System of underwater hydrophones - or SOSUS.

The seafloor sensor that was trapped in the lava flow is formally known as a volcanic system monitor but is often referred to as a "rumbleometer" because of sensors that record volcanic shaking. The sensor was installed on Axial's summit in October 1997 to continue the decade-long effort begun in 1987.

The precise location of the sensor was based on geological and geophysical measurements and was interpreted to overlie the magma center, Fox said. Following the eruption, NOAA vessels visited the site and attempted to recover the instrument.

Although the monitor responded to signals from the vessels, it would not release to the surface. Later investigations using a remotely operated vehicle revealed that the monitor was trapped in the lava flow up to the level of the anchor and was unable to release to the surface. Scientists formulated a plan to recover the instrument in 1999 using the remotely operated vehicle and a powerful ship's winch, and the whole package was recovered with very little visible damage, Fox said.

More surprisingly, "much of the data were intact, in particular the pressure data (which indicates height of the instrument) and the temperature data." Fox said.

The recovered data give a detailed view of the dynamics of a deep ocean volcanic eruption.

Initially, the very thin lava ran beneath the instrument platform and surrounded three legs that stand only 18 inches high. As the edges of the flow cooled and solidified, the lava flow "inflated" and lifted the instrument nearly 10 feet above its initial position in slightly more than one hour. Then the lava supply decreased and "drainback" of the lava began, gently lowering the instrument back to the seafloor in less than two hours, leaving the instrument a little more than three feet above its original position.

Although the instrument was in direct contact with the lava, the temperature probe located within the instrument only rose a maximum of 45.5 degrees during the eruption, perhaps explaining how the onboard data survived, scientists said.

Later field observations of the extent and thickness of the lava flow confirm the details of this scenario, but "without the survival of the rumbleometer, we would never know the time scale of the activity," Fox said.

In addition to the information on the flow itself, the long-term pressure record, in conjunction with other instruments deployed around the volcano by NOAA's Vents Program, provided a picture of what was happening to the magma in the subsurface, making the 1998 Axial event the first deep submarine eruption ever recorded.

"It is doubtful that we will ever be clever enough to intentionally place an instrument in an active submarine lava flow, so this serendipitous recording becomes a benchmark in our understanding of submarine volcanism," Fox said.

NOAA and OSU are expanding monitoring efforts on Axial volcano through the New Millennium Observatory Project. More information on the project can be found on the Web, with a fly-through animation of the "rumbleometer" site.