Science: Volcanoes Never Really Die

Mount St. Helens may have signaled a new wave of eruptions

When Mount St. Helens exploded with cataclysmic fury in 1980, many Americans regarded it as an isolated example of nature on the rampage. Geologists, however, have long known that the restless mountain was only one of many dormant volcanoes in the American West. Although some have not stirred in tens of thousands of years, there is no assurance that one or more will not erupt again, perhaps in the near future. As scientists say, “There is no such thing as a dead volcano.”

To assess when these sleeping giants might violently reawaken, the U.S. Geological Survey (USGS) has been conducting a long-term study of volcanic hazards in the U.S. In an interim report, it has made public a list of 33 volcanic sites in the Western states, Alaska and Hawaii that could go off at almost any time. While the report carefully makes no predictions, it notes that some volcanologists fear that the eruption of Mount St. Helens, as well as other recent signs of seismic unrest in the U.S., may hint at the onset of a period of more intense volcanic activity for Americans.

The initial indication of such terrestrial turmoil came in 1975, when Mount Baker, a 10,750-ft. volcanic peak in northwestern Washington, began to puff and fume. Vented steam has continued to melt ice around the summit crater of the mountain, which is only 90 miles from Seattle. The Geological Survey says that rising magma in the mountain’s cone may be stoking Mount Baker’s internal fires. Magma is hot, melted rock from deep within the earth that fuels volcanoes and becomes visible as lava when it breaks through the crust.

The rise of magma is often accompanied by swarms of small local earthquakes. Such tremors, which enable scientists to estimate how close to the surface the magma may be, have been felt at Mount Hood in neighboring Oregon and at Mount Shasta in Northern California as well as Mount St. Helens. In addition, the USGS study notes that since 1982 earthquakes have shaken California’s Coso Range, a volcanic region west of Death Valley; Yellowstone National Park, which is famed for its hot springs and geysers, notably Old Faithful; and Mammoth Lakes, a popular California ski resort near the Nevada border.

The Mammoth Lakes activity is especially worrisome to the scientists, to say nothing of local residents, who saw a severe drop in tourism immediately after the USGS put the area on its volcano-hazard list last year. The study notes that during the past 1,500 years, the Mammoth Lakes area has been second only to Mount St. Helens in volcanic activity, on the average erupting every two or three centuries along a 15-mile chain of lava domes and old vents. The most recent major eruption took place about 250 years ago, when the area was showered with flaming ash that was, in one scientist’s words, “hot enough to incinerate entire forests.” Moreover, the resort has been repeatedly shaken in the past few years by minor earthquakes, ineluding one in July that registered 5.2 on the Richter scale, a moderately powerful jolt capable of cracking walls, knocking dishes off shelves and causing other minor damage. Scientists have measured at least a 13-in. swelling of the ground near Mammoth Lakes in the past two years, and found that one new hot spring has formed and three other long-dormant hot springs have become resurgent. All this is interpreted as an indication that magma under the region is gradually working its way to the surface.

Some volcanologists caution that far too little is known about volcano behavior to make any firm forecasts about imminence of eruptions. In their view, what seems like multiplying danger signs may, in fact, be a byproduct of the recently intensified monitoring of the earth. Other scientists, however, are sure that the signals are both new and significant. Moreover, because of their recent experience with Mount St. Helens, these volcano watchers have become more optimistic about their ability to make reasonably accurate short-term predictions about the likelihood of an outburst.

Since that May morning three years ago when the Washington peak blew its top, experts have been probing the mountain with every sort of instrument, including seismometers planted within the crater that was formed by the big blast. Every time the volcano twitches, the rumblings are recorded and sent by radio to the University of Washington at Seattle. Mount St. Helens has cooperated by continuing to shake, vent gases and debris and emit lava flows. So thoroughly have the scientists analyzed the interplay of these events that they can now see recognizable patterns in the volcano’s behavior. Some disturbances have served as early warning signs, and over the past three years the scientists have been able to predict 13 minor Mount St. Helens eruptions. The last seven, starting in April 1982, were announced up to three weeks before the actual occurrence. Equally important, none of the predictions were false alarms. With understandable pride, the researchers announced last month in Science: ‘Such repeated accuracy is uncommon if not unparalleled in volcanology.”

That predictive capability may be tested in the future. As the USGS study on volcanic risks points out, the violence that has racked the U.S. in the past is likely to happen again. This time, however, the consequences could be far more serious. Mammoth Lakes and many of the West’s other volcano zones are now the hub of busy recreation centers, many of whose residents are only vaguely aware of the peril that may be building in the ground beneath them. It will be up to the scientists to give them accurate forewarnings of he danger.