From Eons to an Eye Blink for Volcanologists
Geologist Jeff Wynn, in a briefing at the Cascades Volcano Observatory, described how a 925-foot mound of rock inside the crater of Mt. St. Helens had moved 2 1/2 inches in a matter of hours this week. “Imagine,” he said.
The wonder in his voice was barely contained. Not just because the lava dome had moved, but that he and other scientists were able, through sophisticated measuring instruments, to “see” it move -- using technology that wasn’t available to volcanologists 24 years ago when Mt. St. Helens blew its top off in a massive eruption.
There has been a revolution in the study of volcanoes since then, much of it taking place in the Cascade Mountain Range, where U.S. Geological Survey scientists monitor 14 active volcanoes, including Lassen, Shasta and the granddaddy of them all, Rainier.
Mt. St. Helens, the most active and rambunctious of the group, is one of the most scrutinized mountains in the world. With new technology, scientists can detect every spasm, shudder and shake; record every hiss, murmur and moan; and break down the gas composition of a single bubble rising up from the depths while staying at a safe distance.
Most important, scientists can watch the mountain change shape as it is happening, a revolution in itself for a branch of science that traditionally works within the framework of geological time, that is, in the realm of thousands or millions of years.
The new science “lets us work in ‘real time,’ ” said Anthony Qamar, a seismologist at the University of Washington.
Yet for all the advancements, the most crucial aspect of a volcanologist’s job -- predicting the timing and size of eruptions -- is still mostly guesswork.
This is the case with Mt. St. Helens as nearly 80 scientists and researchers -- at the observatory in Vancouver and the university in Seattle -- work around the clock to determine what the world can expect from this latest volcanic episode.
Scientists said Friday that the hardened dome of lava inside the crater continued to grow, indicating that magma was accumulating. They say the magma could eventually be released in a large explosive eruption or, more likely, in a slow ooze or a series of small bursts like the ones that have occurred since the volcano began shaking Sept. 23.
On Oct. 2, scientists raised the alert level to 3 on a three-step scale, indicating that a powerful eruption was imminent. After several explosions that released showy but relatively harmless plumes of steam and ash, scientists lowered the alert level to 2 on Wednesday, meaning that volcanic activity was likely but not threatening to life and property.
Geologists say that the mountain has entered a new eruptive period that could last months, years or even decades. The mountain’s last eruptive period lasted from 1980 to 1986.
The first signs that Mt. St. Helens was reawakening were detected at the University of Washington Seismology Lab in a science building. The lab monitors nearly 300 seismometers in the Northwest, 12 of them on Mt. St. Helens. In 1980, there was only one analog seismometer on the volcano.
The newest seismometers are digital and far more sensitive, about the size and shape of a soup can, and equipped with sensors that detect the slightest ground movement. Readings are transmitted to computers at the university and instantly posted on the Internet.
Seismologist Bill Steele first noticed seismic activity at the mountain -- appearing as squiggly lines on a rolling graph -- a week before the first swarm of earthquakes Sept. 23. Once they began, the swarms accelerated to four small earthquakes per minute. Thousands of earthquakes have since shaken the mountain.
“We got kind of excited,” Steele said, gesturing at stacks of graphs on a nearby desk.
Soon after, geologists began monitoring a growing bulge on the south side of the lava dome, usually an indication of pressure trying to get out.
The old way of measuring mountain deformations -- using surveying techniques involving electronic or laser devices that measured distances between two points -- was time-consuming and risky, partly because it meant scientists had to get close to the mountain to take measurements and then had to enter the information into computers manually.
That method has been replaced by a Global Positioning System that can detect movements of as little as half an inch on the mountain 8,363 feet above sea level. The system, developed by the U.S. Defense Department for navigation, pinpoints locations on Earth with the help of satellites.
There are 10 GPS receivers on the mountain -- with three in the crater -- that transmit data to computers at the Cascades Volcano Observatory. The receivers can be as small as a cigarette pack, and are usually powered by batteries or solar panels.
Scientists can get readings every second.
One USGS scientist, Ralph Haugerud, uses a GPS receiver in combination with lasers and computers to create detailed topographical maps five feet wide that show incremental changes in the terrain. The technology, called Light Detection and Ranging, is installed in an aircraft and can take up to 20,000 pictures per second.
Haugerud’s maps are posted on the walls of the seismology lab, where scientists pore over every new crack and crevice.
“This helps to give you the big picture,” Haugerud said as he posted the newest map showing several hundred square miles around the mountain.
Small planes and helicopters have also been carrying new gas analyzers designed to detect the presence of magma. Once or twice a day, an aircraft with a hose in front will fly over the crater, taking in gases that are piped into machines and analyzed instantly. Carbon dioxide, sulfur dioxide or hydrogen sulfide indicate the presence of magma, which would be the most likely cause of an eruption.
USGS geologist Jake Lowenstern said he was convinced that there is a growing deposit of magma under the southern edge of the lava dome.
“We don’t think there’s a large amount, but we think it’s there,” he said, probably 100 meters to 200 meters below the surface.
Scientists have also installed two highly sensitive microphones on the mountain’s east and west flank that pick up the slightest noises, such as a breeze, a rock fall, or the movement of magma.
But even with all these instruments, scientists still can’t monitor what’s going on in the most important part of the volcano: the interior.
“That’s where the activity is,” Lowenstern said. Measuring instruments of any kind would probably be destroyed if they were placed inside the mountain.
Because of this information gap, the mountain’s behavior will still be largely unpredictable, scientists said. That was one of the key lessons of the May 18, 1980, eruption that killed 57 people, leveled forests and sent ash around the globe.
On that day, a magnitude 5.1 earthquake caused a massive landslide and the collapse of the volcano’s north slope, releasing pressure and producing a lateral blast -- something no scientist predicted.
