Rainier's Past A Clue To Future

Geology: Warnings about potentially devastating hazards posed by Mount Rainier have become more frequent. Now scientists are gathering geological data that may lead to better forecasts of the mountain's activity. ---------------------------

On clear days, even longtime area residents say the sight of Mount Rainier on the horizon can take their breath away. The spectacular facade serves as a reminder of nature's grand scale and its seeming impassivity before the tiny movements of the human race.

But, although certainly grand, nature is anything but impassive, and for volcano researchers, awe at Mount Rainier's majesty is heightened by knowledge of the volcano's potential for destruction.

Mount Rainier, which last erupted about 150 years ago, remains active and will almost certainly erupt again. With at least 100,000 people living in the valleys that have historically drained the volcano's debris, a major eruption could kill thousands and cripple the region's economy.

Yet, despite the hazards the volcano poses, Mount Rainier has received relatively little scientific scrutiny. The last major studies of the volcano date to the 1950s.

"Study of Mount Rainier has been a relative backwater," acknowledged Don Swanson, a geologist with the U.S. Geological Survey (USGS) and an affiliate professor at the University of Washington.

Researchers are now working to change that. The International Association of Volcanology and Chemistry of the Earth's Interior has designated Mount Rainier for focused research as part of a decade-long U.N. project aimed at reducing losses in natural disasters. The 14 volcanoes designated for study lie near well-populated areas in 12 nations but have not previously been examined extensively.

Over the next several years, geologists and geophysicists will collect data at Mount Rainier for scrutiny at government and university laboratories throughout the nation. The final result will be a better understanding of Rainier's past, which scientists hope to use to predict and plan for its future.

Instruments in place on the mountain constantly monitor Rainier's activity. Because movements in the Earth precede volcanic eruptions, seismic monitoring of Rainier will likely provide some warning of imminent eruption.

But warning systems are not infallible, and Dan Dzurisin, scientist-in-charge of the USGS Cascades Volcano Observatory, explained that simply knowing an eruption was coming might not be enough to form effective plans of action, primarily because eruptions differ in type and magnitude.

"If you took the pulse of a volcano and heard a lot of earthquakes, you would think an eruption was coming," Dzurisin said. "But, if you hadn't studied the volcano's past, you wouldn't know what kind of eruption."

Moreover, some volcanic hazards can occur independent of eruptions.

By carefully studying a volcano's past, researchers can see what kinds of eruptions have occurred and with what frequency. They can then project that knowledge into the future.

"If we get a good idea that a volcano has behaved in a certain fashion in the past, it's reasonable to think that it's going to behave that way in the future," Swanson said.

Mount Rainier's past has been recorded in the myriad rock deposits that make up the volcanic edifice and the surface of surrounding areas.

For hundreds of thousands of years, each eruption layered a new deposit atop an old one. In Rainier's crevices and outcroppings, the successive layers can be seen. From the mineral composition of the rock, geologists can distinguish the layers from one another and determine the different kinds of volcanic events that created them.

Layers produced by explosions contain large amounts of pumice and gas. Those that resulted from lava flows are largely composed of silicon and have a lower gas content. Mud and debris flows, called lahars, produce matrices of sand, mud and clay.

Through radiometric dating, scientists can tell when the events occurred.

Knowing the age and composition of the mountain's many deposits, researchers can chart geological maps of Mount Rainier that detail its volcanic history and its effects on surrounding areas. With that information, researchers can determine the likelihood that specific volcanic events will be repeated in the future and what areas they will affect.

Rainier lacks such geological maps because previous studies did not adequately differentiate the various deposits, Swanson said.

"Those studying the mountain in the past didn't look at the mountain in any detail," Swanson said. "They labeled everything on the volcano as the same kind of rock."

Labeling everything is quite a task. The lack of extensive studies of Mount Rainier is largely a result of its harsh terrain, which is steep and covered by snow and ice.

"This kind of study takes people who have substantial mountaineering skills," said USGS geologist Tom Sisson, "people who aren't going to get lost up there."

Sisson and a team of geologists are working near the summit. The team collects rock samples to be analyzed at laboratories for age and chemical composition. Sisson estimated it will be six years before a geological map can be drawn.

From a hazard-reduction standpoint, mapping deposits left by lahars is of primary importance in the case of Mount Rainier.

In the event of a major eruption, lava flow and ash would be most devastating in the volcano's immediate vicinity, probably within the area of Mount Rainier National Park. But the heat generated by an eruption could immediately melt large volumes of the snow and ice that cover the volcano. The melt water racing down the sides of the volcano could in turn generate much larger mud and debris flows.

These lahars could travel long distances at high speeds toward populated areas. Five millenniums ago, a lahar from Mount Rainier reached Puget Sound, engulfing the sites of present-day Puyallup and parts of Tacoma.

The melting of frozen precipitation is not the only cause of disastrous lahars. The movement of hot water through rock, induced by rising magma, can break rock down into clay, rendering it unstable and subject to collapse.

Mount St. Helens provided an example of edifice collapse to volcano researchers when its north flank bulge collapsed during the 1980 eruption, creating the largest landslide in recorded history.

Unstable volcanic rock could also collapse in earthquakes or even in rainstorms, without evidence of eruption.

The 1985 eruption of Colombia's Nevado del Ruiz was less than a 20th the size of the 1980 Mount St. Helens eruption, but that relatively small eruption created lahars that traveled more than 20 miles to bury the town of Amero, killing 23,000 people.

Barry Voight, a Pennsylvania State University geologist who is studying structural collapse on Mount Rainier, cited the Ruiz disaster as one brought on by ignorance of the volcano's past. Armero had been built on the lahar deposits from eruptions in 1845, 1595 and earlier.

Having a comprehensive geological map could have allowed emergency planners to prepare an evacuation effort.

Indeed, if the town's 19th-century founders had had access to such a map, a community might never have developed in such a hazardous area.

Voight said detailed geological mapping of Mount Pinatubo in the Philippines led to a very different outcome when that volcano erupted in 1991.

"At Mount Pinatubo, they had mapped the volcano in such detail that they knew where the hazards were and they subsequently evacuated 200,000 people," Voight said. "I can't think of better decision-making in a crisis situation."

It will be harder to use such information for long-term community planning, though. Although researchers certainly want to share their findings with public policy-makers, the warnings are often difficult to translate with any urgency.

Geological time is grossly out of scale with human time. Although Mount Rainier is in the most active phase of its existence in geological terms, it could remain dormant for decades or even centuries. And growth associated with human progress is rarely planned with an eye toward that long a term.

Sisson said people living near Mount Rainier need to think of a "significant" time span, not only in terms of their own lifetimes but also those of their children and grandchildren.

"In that respect," Sisson said, "it is very likely that something will happen within a time span that is significant for the surrounding communities."