By Thomas Guengerich
SOCORRO, N.M., Nov. 25, 2008 – New Mexico Tech geophysics professor Dr. Jeffrey Johnson is getting double exposure for his successful volcano field work. His research in Guatemala is getting attention from the National Geographic Society and the prestigious journal Nature.
While the National Geographic attention is glamorous, the publication of his article in Nature represents an academic milestone.
Johnson is the lead author of an academic paper that relates volcanic eruptions to earthquakes in a novel way. His research was summarized in an article titled “Long-period earthquakes and co-eruptive dome inflation seen with particle image velocimetry” published in the November 21 issue of Nature.
Johnson, who joined New Mexico Tech’s faculty in January 2008, had made a research trip to the Santiaguito volcano in January 2007.
“Nature’s interest in our results affirms a broad scientific and public interest in our work that extends beyond the volcanological and seismological communities,” he said.
When Johnson and his team return to Santiaguito in late December 2008, a film crew from National Geographic’s show “Wild Chronicles” will also tag along to document the work, which includes an element of adventure and mountaineering coupled with science. Johnson and his students’ travel is being funded by a National Geographic expeditions grant that is allowing an extension of previous research supported by the National Science Foundation.
Left: Jeffrey Johnson making observations of the erupting Santiaguito volcano from the Santa Maria mountain in Guatemala.
Santiaguito’s active vent is a volcanic dome that has a flat surface about the size of five football fields. During the previous research expedition in January 2007, Johnson’s team recorded many eruptions with earthquake monitoring instruments and with video cameras, including conventional and thermal. Back in the lab while analyzing data, his team discovered that the eruptions were concurrent with a quick uplift of the entire surface of the volcanic vent.
“The whole rock surface moves upward 20 to 50 centimeters within a few seconds as the volcano explodes,” he said. “The surface inflates dramatically and it’s really exciting because no one has ever seen this before. Essentially we are witnessing an earthquake with a video camera.”
The laws of physics dictate that the great force of rocks moving upward must be accompanied by an equal force directed downward.
“We’ve shown that this upward movement is responsible for earthquakes,” Johnson said. “We’re able to quantify the earthquake parameters with optical tools.”
“For a while now I’ve been interested in recording earthquakes in order to be able to infer what’s happening at the vent when you can’t see the volcano,” he said. “I always deploy both seismometers and infrasonic microphones – a tool capable of quantifying the concussions in the atmosphere. Whenever possible I also utilize a video or time lapse camera trained on the volcano to have another corroborative data point.”
After returning from the field in 2007, a graduate student first noticed the video of an explosion in slow-motion and thought he saw the slight movement of the solid lava at the onset of an eruption.
Johnson quickly wrote a program that would interpret, track and measure the movements via particle image velocimetry.
“The quantified dome movement is achieved with a high-definition consumer camcorder and computer software,” he said. “Quantifying this movement provides us with invaluable geodetic information about the earthquake source.”
Via the optical measurements, Johnson can extrapolate the intensity of the earthquake – all in an effort to better understand the mechanics of the eruption and the relationship to earthquakes.
“The thing about earthquakes is that we understand tectonic earthquakes very well – those associated with fault rupture,” he said. “They have predictable mechanisms and we effectively understand their mechanisms. It’s two rocks fracturing along a planar surface.
“Not true for volcanoes,” Johnson said. “They produce all these ground tremors that aren’t readily associated with known source types. We record tremors, but we don’t know always the source.”
Johnson’s research contributes to the understanding of the forces at work inside an active volcano. “We show a long-period earthquake is associated with an abrupt surface movement and we can attribute the seismic response to a vertical force.”
Johnson is the leader of a multi-institution, multi-agency team that expects to produce many more academic papers about this phenomenon.
When he returns next month, Johnson will have six time-lapse cameras and a contingent of broadband seismometers on loan from the PASSCAL Instrument Center, which is the world’s largest lending library of seismic instruments and, conveniently enough, is located at Johnson’s home institution, New Mexico Tech.
The National Geographic Society is helping fund three expeditions over the next 12 months to active volcanoes in Ecuador, Guatemala and Chile. The first of these trips will be to Santiaguito in Guatemala.
Conducting research at Santiaguito is not for the faint of heart or weak of knees. The active dome is accessible only by foot. Johnson, who is fond of climbing mountains, said the trail is rough and the hiking is difficult – especially when carrying car batteries and other heavy equipment.
“We travel to Santiaguito specifically because of the incomparable view of the active dome from the summit of a higher peak,” Johnson said. “It’s a difficult hike to get to the top of the neighboring 13,000 foot volcano and cold camping there, but the view of the volcanic activity from up there is spectacular.”
The team will climb Santa Maria, the parent volcano to Santiaguito, which erupted in 1902 with an intensity 10 times larger than the 1980 eruption of Mount St. Helens and twice as big as the 1990 eruption of Mt. Pinatubo in the Phillipines. That volcanic explosion created a massive crater, out of which sprung four lava domes. Santiaguito’s Caliente Vent is currently the only active dome among the four. Santa Maria stands between the closest city, Quetzaltenango, and the dome. On the other side of the domes is an inaccessibly dense jungle.
The researchers ascend about 4000 vertical feet from the trailhead to the crest of Santa Maria, the volcano that erupted in 1902. The scientists will also cross the shoulder of Santa Maria, then descend into the crater to set up seismometers nearer to the dome that erupts regularly about once per hour. The initial climb is strenuous, but the descent to the dome is even more difficult.
Cameras will be placed along the Santa Maria ridge that faces the volcano. Johnson and his colleagues from Michigan Technological University must also place the seismometers around the active dome.
Johnson was able to obtain his coupled volcano-earthquake results through support from the National Science Foundation Division of Earth Science. Johnson is now continuing his research in volcanology and geophysics with another current grant that is aimed at probing the interior plumbing of volcanoes. Titled “Near-Field Volcano Infrasound: 3-D Seismo-Acoustic Wave Propagation,” Johnson’s ongoing research aims to precisely understand the cause-effect relations between volcanoes and earthquakes, elastic wave propagation, and other eruption-related phenomena.
“Santiaguito is one place where we are able to address all these issues,” he said. “It’s a wonderful volcano lab. It’s always active and, because we can look down on the dome from Santa Maria, it has viewing geometry that is unsurpassed.”
– NMT –