BY MARK SHWARTZ
Sigurjon ("Sjonni") Jonsson will never forget the first time he experienced the awesome power of a volcano.
"When I was growing up in Iceland, there were nine volcanic eruptions less than 20 miles from my home," he recalls. "I remember going to bed as a small child and seeing the bright red sky out my window."
A typical family excursion for young Sjonni often meant driving to an erupting volcano to get a closer look. He enjoyed the spectacle of hot lava and ash spewing from beneath the earth, although authorities made sure that he and his family kept a safe distance away.
Now a graduate student in geophysics, Jonsson has turned his childhood fascination with volcanoes into a scientific passion. Instead of driving to the edge of a bubbling caldera, he uses sophisticated satellite imagery to measure subtle volcanic activity from the comfort and safety of his Stanford research lab.
His research has already yielded one surprising discovery about the Galapagos Islands, located half a world away from his native Iceland. Satellite analysis shows that the Galapagos may be home to the most concentrated collection of active volcanoes on the planet.
This satellite radar image shows the western Galapagos Islands of Fernandina and Isabela, which contain the largest known concentration of active volcanoes in the world. Six of the seven volcanoes found here are active, including Cerro Azul and Fernandina, which erupted in the 1990s. Ecuador is the only volcano that appears to be dormant.
Amelung & Jonsson, Stanford
Located off the Pacific coast of Ecuador, the roughly 20 volcanic islands that make up the Galapagos archipelago have been an inspiration to scientists ever since British naturalist Charles Darwin made his famous voyage there in 1835.
"A number of volcanoes in the Galapagos have erupted since Darwin's time," Jonsson points out, "but until we did our satellite research, people didn't know that so many volcanoes are currently active."
Jonsson and his Stanford colleagues collect data on the Galapagos from specially designed satellites that bounce radar waves off the surface of the islands from 500 miles in space. The satellites are capable of creating remarkably detailed radar images of volcanoes and other land formations in cloudy or clear conditions.
By comparing two satellite "snapshots" taken on different days, scientists can detect tiny changes in the movement of the earth. Even the slightest alteration in the size or shape of a volcano indicates underground activity that may result in an eruption.
Jonsson's team has focused its attention on the two most geologically active islands in the Galapagos chain: Fernandina and Isabela. (See map.)
Fernandina consists of a single volcano that erupted in 1995. Neighboring Isabela, the largest island in the Galapagos, is made up of six volcanoes, including Cerro Azul ("Blue Hill") which erupted in 1998.
Isabela's other five volcanoes, including one named Darwin, were thought to be inactive until Jonsson and former postdoctoral candidate Falk Amelung demonstrated otherwise.
"We compared two satellite images of Fernandina and Isabela taken on two separate days -- one in 1992, the other in '98," Jonsson explains.
Their analysis revealed that four of Isabela's volcanoes had risen during the six-year period: Wolf, Darwin, Alcedo and Sierra Negra.
The rate of change in each volcano varies considerably from the northern end of Isabela Island to the south. Wolf volcano in the north has only grown about 4 inches taller, but Sierra Negra in the south has risen more than 8 feet -- a substantial increase made all the more ominous because Sierra Negra experienced a major eruption in 1979.
"People knew that Sierra Negra is active," Jonsson observes, "but it was a total surprise that the three northern volcanoes [Wolf, Darwin and Alcedo] are also uplifting."
When he presented his findings at the annual conference of the American Geophysical Union in San Francisco in December, Jonsson says volcanologists were "really amazed" to learn about the discovery of six active volcanoes in an area less than 40 miles across. In fact, the Galapagos may be the first place on earth where so many active volcanoes have been found clustered so close together.
Of the seven volcanoes in Jonsson's study, only Ecuador showed no increase in size and is therefore believed to be dormant.
Satellite imagery revealed that Fernandina volcano, which erupted in 1995, is rising again, but Cerro Azul has subsided about 7 inches since its 1998 eruption.
The recent Cerro Azul eruption made international headlines when the Ecuadoran army came to the rescue of giant Galapagos tortoises threatened by rivers of molten lava. Because a single tortoise can weigh more than 500 pounds, helicopters were required to airlift the endangered reptiles to safety. (See sidebar.)
Although Fernandina and Isabela Islands have few human inhabitants, Jonsson believes that satellite radar imagery will be an invaluable tool for detecting volcanic activity in densely populated areas of the world.
Geophysics Professor Paul Segall agrees.
"Our dream is to monitor all 500 to 1,000 active volcanoes on earth without actually going there," he says, adding that thousands of lives could be saved if satellite imagery determined that supposedly dormant volcanoes are indeed active.
Segall also points out that detecting volcanic activity on the ground can be dangerous, and that several volcanologists have been killed in recent years at Mount St. Helens and at other sites around the world.
Segall and Howard Zebker serve as graduate advisers to Jonsson. Zebker, who holds joint professorships in geophysics and electrical engineering, pioneered the satellite radar imaging technique known as Synthetic Aperture Radar (SAR) Interferometry that Jonsson used in his analysis of the Galapagos.
So far, neither Zebker nor Segall can explain the large cluster of active volcanoes on the Galapagos.
"We don't really understand this at all," Zebker says, "which is what makes it exciting."
"It's amazing that a grad student at Stanford can learn about the Galapagos without ever going there," Segall adds.
Jonsson would like to visit the Galapagos some day and follow in the footsteps of Charles Darwin. For now he is content gathering new satellite data and trying to unravel the mysterious geology underlying these fascinating islands.
"We're seeing something new and
unexpected in the Galapagos," Jonsson says. "That's always
interesting in science." SR