UNH Scientist At Mount St.
Helens To Wire Rumbling Volcano With Microphones
Contact: David Sims
Institute for the Study of Earth, Oceans, and Space
Oct. 7, 2004
UNH Professor Jeff Johnson will return to Durham Oct. 15 and can
be reached at (603) 862-0711. He can also be reached via Email at:
DURHAM, N.H. -- When volcanoes rumble, Jeff Johnson listens –
So when Mount St. Helens began stirring recently, Johnson knew he’d
be making a visit to Washington State to “listen” to
the volcano that erupted with such force in 1980. A Fulbright Scholar
at the University of New Hampshire’s Institute for the Study
of Earth, Oceans, and Space (EOS) and Department of Earth Sciences,
Johnson holds a Ph.D. in geophysics.
Johnson headed to Seattle Oct. 6 to help interpret the acoustic
and seismic data from Mount St. Helens as he's done for years at
volcanoes across the globe.
"My primary role is to analyze and understand the recorded
acoustic 'wiggles', which are a graphical representation of sound
waves too low in frequency for humans to hear," Johnson says.
Colleagues from the Pacific Northwest Seismograph Network at the
University of Washington and the United States Geological Survey
Cascades Volcano Observatory worked in concert during the last few
days to install microphones similar to the one Johnson and others
have recently deployed at a volcano in Ecuador.
Says Johnson, "The first microphone was deployed at the volcano
only three days ago about four kilometers from the dome of Mount
St. Helens, and its information is being sent in real time via radio
telemetry to the University of Washington.”
The idea, he explains, is to be able to understand when there are
gas emissions (explosions or less vigorous degassing) even during
periods of time that there is no clear line of sight to the dome
(i.e., the explosions can't be visibly confirmed).
“We focus on ‘infrasound,’ low frequencies inaudible
to humans, because this is the type of sound that volcanoes typically
emit with great intensity,” he says. “Detecting and
analyzing these sounds can provide an important complement to other
forms of eruption monitoring."
Mount St. Helens is one of a dozen active volcanoes where Johnson
has studied volcanic infrasound. Most recently, he has been working
in Ecuador at the active volcano Tungurahua. Since 1999, this volcano
has threatened tens of thousands of citizens living in nearby towns
and rural communities and induced mass evacuations.
Over a period of years, Johnson, in collaboration with observatory
staff at the Geophysical Institute in Quito, earth scientists from
the University of North Carolina, computer scientists at Harvard
University, researchers at the United States Geological Survey,
and engineers at University of Washington, has worked in Ecuador
to better understand the threat and develop instrumentation to minimize
A successful pilot project to Ecuador was carried out in July 2004
to implement a new wireless microphone array that could better track
the ongoing eruptive activity at the volcano. The instruments were
installed at a remote location 11,000 feet high on the flanks of
the exploding volcano. The goal was to listen to the low-frequency
rumbles, which are associated with eruptive events including ashy
explosions, gas exhalations and paroxysmal bursts that can eject
glowing boulders the size of Volkswagens.
"Monitoring the sound radiation from Tungurahua is one of the
most effective means to keep tabs on the ongoing state of the eruption
at this dangerous volcano," Johnson says. "More often
than not, the summit of this volcano is hidden behind dense clouds
so we can’t see if an eruption is in progress. Furthermore,
seismic recordings are often unable to illuminate whether an eruption
has occurred because it is hard to differentiate the ground motions
associated with explosion events and sub-surface earthquakes."
The wireless array of sensitive microphones at Tungurahua was situated
close to the volcano’s throat, where it was able to record
sound waves and transmit the data to the permanently manned volcano
observatory nine kilometers away. Scientists at the observatory
are then able to filter out noise and visually identify explosion
events, which provide at indication of the state of volcanic unrest.
Tracking this unrest over time and observing trends in explosive
degassing is vital for predicting potentially catastrophic changes
in eruptive behavior.
Says Johnson, "The acoustic monitoring of volcanoes is becoming
more and more commonplace at volcanoes worldwide. Now that Mount
St. Helens is awakening, we have the opportunity to test and utilize
this important technology in our own back yard, in the United States."