On Shaky Ground

by Nance, John J. ;

  As much as the original paper Dr. Press had written in 1965 on earthquake hazard reduction, as much as the decade-long efforts to enact the 1977 earthquake hazards reduction bill, that one exchange between the President’s science advisor and the occupant of the Oval Office pushed the national understanding of earthquake threats past another milestone. By the time Air Force One reached the ramp at Andrews Air Force Base near Washington, D.C., the framework for a rejuvenated look at the problem was in place—even as the puzzle of what was to become of Mount St. Helens deepened back in America’s other Washington.

  More than the ash plumes which continued to spout from the crater, more than the destruction of vast square miles of forests and industrial installations, the partial damming of the Columbia River, and the threat to the state’s resources in dealing with the cleanup, there was a growing concern in Washington: Was life in the Pacific Northwest going to be the same? What had always been a beautiful, picturesque area of wooded landscapes and mountains, rivers, and inland waterways was becoming a periodic ashtray for the now squat and ugly mountain which had changed its personality overnight.

  The problem was the uncertainty, and the inability of anyone in the physical sciences to answer the question: What now?

  The last major eruption along the Cascade volcanic chain had rocked Northern California in 1914 with the beginning of a three-year eruption of Mount Lassen which included some spectacular displays of capricious behavior on the part of the mountain (at one point it chased a forest fire lookout down the mountainside by hurling boulders the size of houses at his lookout tower). Would St. Helens rain ash clouds on the area for three years, or more? The prospect was very depressing. Residents of Yakima and Spokane (both covered by the ash plume’s initial fallout), along with their fellow Washingtonians on the western side of the mountains from Vancouver, Washington, north to the Seattle-Tacoma area, were tiring fast of waking up to gritty coverings of gray ash. As the days immediately following the eruption had shown, St. Helens’ ash could grind an engine down to a major repair bill in no time, as well as ground aircraft and imperil health.2

  But it did appear that there would be no more cataclysmic explosions. The seismic activity beneath the mountain seemed to confirm that the May 18th explosion had relieved the lion’s share of the pressure, and other than sporadic throat-clearing eruptions and dome-building lava flows, the mountain and the population of the Pacific Northwest might even learn how to coexist—though periodic tremors felt as far north as Seattle would continue to raise questions of what, exactly, was occurring below, and the worrisome question of whether seismic or volcanic activity touched off by St. Helens could reactivate Mount Rainier.

  It was a chicken and egg argument, the relationship of volcanoes and earthquakes. Sometimes, as with St. Helens, an earthquake could trigger the final phases of a volcanic reawakening, setting the stage for (or actually causing) a major eruption. Were the earthquakes themselves, though, caused by volcanic activity below? Obviously the movement of subterranean rivers of glowing magma was what created the episodic (or, at a more developed state, harmonic) tremors so familiar to volcanologists and seismologists monitoring volcanoes. But where did the other earthquakes surrounding such events as St. Helens fit into the puzzle? Which, in fact, came first? The volcanic or the seismic event?

  Since the acceptance of the plate tectonic model, one thing seemed certain: The movement of the plates provided the principal engine for most volcanic activity worldwide.

  The Cascade chain of volcanoes, for instance, is very similar to numerous other volcanic mountain chains throughout the world in that it is the direct result of plate subduction. Chains such as the Andes Mountains in South America, or the string of volcanic peaks on the Aleutian Islands in Alaska, are formed when the oceanic plates which are being consumed beneath the continental plates melt into magma. That magma—usually rich in silica—is lighter than the surrounding rock structures (which are as much as fifty kilometers [thirty miles] beneath the surface of the earth), so the colossal blobs of newly liquefied rock, thousands of degrees hot, begin rising to the surface, melting overlying rock layers as they ascend, taking thousands of years for the inverted teardrop-shaped masses called plutons (sometimes measuring miles across) to reach areas beneath established volcanic chains, where they fill faults and tubes and other venting systems which can energize anew an existing volcano. (Old, cooled plutons now lay exposed as the Half Dome and El Capitan mountains in Yosemite National Park in California.) It is such plutons which fuel the eruptions of volcanoes such as Washington’s Mount St. Helens.

  But no one yet knows what role earthquakes—especially great subduction zone earthquakes—may play in the process of accelerating the plutonic masses of molten rock in their journey to the surface.

  All up and down the coast of the Pacific Northwest the evidence of this process can be seen from the ground, from the air, or on a map. The majestic beauty of Mount Shasta in Northern California; the collapsed remains of a mountain we now call Mount Mazama (Crater Lake) in southern Oregon; the Three Sisters in middle Oregon; Mount Hood east of Portland, Oregon; Mount Adams, St. Helens, Rainier, and Baker in Washington; and Mount Garibaldi in British Columbia—all are stark evidence of the presence of a subduction process many kilometers below—and evidence of the approximate point inland from the seashore where the Pacific plate is melting thirty to fifty miles beneath. In fact, the reason that Mount Lassen (to the southeast of Shasta in North California) is the southernmost member of the northwestern volcanic mountain chain can be seen on any tectonic map: Lassen marks the approximate southern limit of the Cascadia subduction zone along the Pacific Northwest coast. (From that point south, the two great plates are sliding past each other along the planetary crustal seam of the San Andreas Fault.)3

  Like the mythical phoenix, small amounts of the consumed oceanic plates rise again, their remelted material forming the very rock of such mountains as Fuji in Japan (near Tokyo) or Mount Rainier near Seattle and Tacoma (originally called Mount Tacoma).

  But there are other types of volcanoes. Hot spots such as that which formed the Hawaiian island chain channel basic basaltic magma from the earth’s mantle to the surface without the mixtures of silicas and other minerals found in the remelted crustal rock of subduction zones.4 There is, in fact, a hot spot beneath the continental United States. A massive pluton—magma chamber—which sits beneath Yellowstone National Park energizes the geysers and the other geothermal activity which, in our geologically brief time on this continent, has attracted so much attention and justified our first national park.5

  And, there is the sort of volcanic region which results from the tectonic stretching of the crust of the earth, a process which thins the crust and permits magma from the mantle of the earth to intrude into the cracks, rising to the surface to form the type of volcanic region still visible in northeastern New Mexico and southern Colorado—and in recent times just to the east of the High Sierras in California.

  In the area due east of Yosemite between the rising Sierras and the White Mountains, north of the present-day town of Bishop at the head of the Owens Valley, a huge mountain rising perhaps fifteen thousand feet stood with a volcanic bomb in its heart less than a million years ago. Fueled by basaltic magmas rising through a thinning crust (a hundred miles from the nearest subduction zone), the mountain disintegrated in a thunderous planetary cataclysm some seven hundred thousand years ago—an explosion of ash and clouds of glowing pyroclastic plasma which makes the explosion of Mount St. Helens seem totally insignificant by comparison. St. Helens blew one-quarter of a cubic mile of rock and ash into the air on May 18, 1980. Before that it had thrown out 1 cubic mile around 1900 B.C. Mount Mazama’s explosion which resulted in the collapsed caldera that formed Oregon’s spectacular Crater Lake ejected 10 cubic miles of rock in 4600 B.C., and in more recent times, in 1815, Indonesia’s Mount Tambora blew 19 cubic miles into the atmosphere (compared with Krakatoa’s 4.3 cubic miles in 1883) as it killed twe
lve thousand people and caused the “year without summer” of 1816.

  But when the mountain which sat to the south of present-day Mono Lake blew up, it injected a staggering 250 cubic miles of rock and pulverized mountain into the atmosphere, spreading a layer of ash as far east as Nebraska, undoubtedly darkening the atmosphere of the earth for several years, and leaving behind a collapsed caldera to cap the throat of the spent volcano. The rubble from the collapse formed a roof over the spent magma chamber (which had been reduced to one-quarter of its previous volume) and formed a beautiful high-altitude desert floor ringed by the remnants of the former volcano’s flanks—an awe-inspiring area which seven hundred thousand years later was named Long Valley by the humans who had so recently arrived in the last few seconds of geologic time. Into this eight-thousand-foot-high setting of ponderosa pine and active hot springs came a trickle of prospectors and miners, following Indian trails and building boom towns and mining camps in the High Sierras, followed by ranchers and cattlemen and farmers, who eventually gave way to the interests of a distant, growing California metropolis (Los Angeles) which began to drain the area of water in the early twentieth century, reducing the agriculture and leaving the high terrain of Long Valley with only one significant economic activity: the status of being a resort community dependent on tourism.

  It was this valley that had been tagged as a seismic gap in 1978, a prediction hardly noticed by the residents of the resort community of Mammoth Lakes within the southwest rim of Long Valley—residents who were quite used to small tremors.

  And it was the community of Mammoth Lakes that found itself catapulted into a seismological-volcanological mystery which began with a series of four moderate earthquakes of magnitude ML 6.0, 5.8, 5.8, and 5.9 all on the same day of May 25, 1980, just before the economically important Memorial Day weekend, and precisely one week after the explosion of Mount St. Helens.

  Chapter 19

  Mammoth Lakes, California—August 25, 1982

  Denial.

  The reality was, quite simply, that these people did not want to believe the facts. Their town was literally sitting on a volcano that might be ready to erupt, but the residents were refusing to accept the truth.

  The panel of scientists from the USGS, the California Office of Emergency Services, and the California Division of Mines and Geology had come together for a long-delayed meeting with the outraged community of Mammoth Lakes—and it was turning into an agonizing encounter, to say the least.

  For scientists such as Dr. Roy Bailey, the USGS volcanologist who had helped trigger the alert to begin with, the anger made no sense. Scientific facts were scientific facts. He and his colleagues were only reporting them—telling Mammoth Lakes a truth they obviously did not want to hear. In that, the USGS was merely the messenger, bringing the unwanted news that Mammoth Lakes might be facing a major and deadly volcanic eruption. But from the emotional and angry attitudes in the room, it was obvious that the survey had become the enemy—a messenger the townspeople wanted to strangle.

  “You people have destroyed this community! You’ve … you’ve gone off half-cocked and scared everyone to death with this stupid warning, and now you tell us that you really don’t know if anything is going to happen or not. Why the hell did you go shooting off your mouths to the press and destroying our season before you had any idea whether there’s a threat or not?” The angry businessman, face flushed with anger, regained his seat as his neighbors applauded, many other frowning faces nodding in agreement throughout the room. It had gone that way since the meeting began. After three months of bureaucratic fumbling among the various government agencies over the date and location for a public meeting to explain the USGS warning, tempers had grown very short. Many local merchants were facing a lean winter after a curtailed summer season, and the opportunity to broadside the “egghead scientists” who had “caused the problems in the first place” was not going to be lost. It was, it seemed, open season on USGS volcanologists. In fact, to some of the men on the panel (sitting on the raised stage at the northeast corner of the auditorium and feeling just a bit cornered), the level of upset sparked old movie images of indignant villagers carrying lighted torches and dark resolves.

  To hear these people tell it, Bailey knew, the USGS had maliciously devastated the community’s economy by issuing a Notice of Potential Volcanic Hazard. (Some even openly accused the survey of timing the notice to help somehow with new USGS budget requests on Capitol Hill!)

  But as Dr. Bailey knew, a major cause for the anger had been the outrageous way the people of Mammoth Lakes had been told that their beautiful little community might be facing a volcanic nightmare. More accurately, it was the way they had not been told—at least not by the USGS. The information had come in the form of a newspaper story from Los Angeles.

  Somehow the information on the upcoming USGS warning had leaked to Los Angeles Times science writer George Alexander, who broke the story under the May 25th headline MAMMOTH AREA TREMORS HINT VOLCANISM. The USGS had dated and sent the formal release the same day, sending copies to a long list of government and community leaders by regular U.S. mail. Predictably, however, the Los Angeles Times arrived first.

  No one in the Mono County government, no one in the community of Mammoth Lakes, nor anyone in the Chamber of Commerce had been told of the warning before copies of the paper reached the public on the twenty-fifth. Mammoth Lakes community leaders, such as Gary Flynn and Gail Frampton (both in the real estate business and already fighting tough times), had been shocked, horrified, and infuriated, in that order.

  The perceived discourtesy was bad enough, but it was just the beginning. The USGS notice unleashed instant national publicity, echoing across the nation on TV, radio, and wire services, telling the world various versions of what Alexander had accurately reported. In some publications Mammoth Lakes was simply in danger; in a few it seemed on the verge of annihilation (as would be anyone foolish enough to travel there, it was implied). In perhaps the most bizarre version, lava was reported running through the streets of the town. Whatever the outside world was told, there was one thing made quite clear: Mammoth Lakes was a potentially dangerous place to spend a vacation.

  And all this descended on the resort a mere six days before the biggest weekend of the year, the Memorial Day influx of tourists and tourist dollars which inevitably led to new condominium sales, booked-up hotels, packed restaurants, and as much as 15 percent of the gross revenues of the year for some businessmen. The timing of the USGS notice and the perceived “holocaust” of negative publicity could not have been worse. Mammoth Lakes had already been reeling from a national recession and an overbuilt real estate market. Now, suddenly, people began calling Long Valley with cancellations, erasing many hotel reservations, collapsing real estate deals like a house of cards (most recreational real estate sales in escrow were dumped within hours), and inundating the Chamber of Commerce in the unincorporated community with worried inquiries about friends, relatives, and summer homes thought to be in harm’s way. One caller phoned specifically to ask if “the lava has cooled enough for us to take pictures [of it].”1

  The shared opinion of many local merchants and real estate brokers in the first week following the botched release was that their federal government could hardly have hurt them more had the Air Force simply lobbed a bomb into the center of town. For a community so completely dependent on summer tourism, the economic damage attributed to the USGS warning seemed the final straw—and far worse than any coup de grace which might be administered by any volcanic explosion. The conclusions were ridiculously apocalyptic, and the rhetoric hyperbolic; but to the business community, those conclusions reflected the financial damage they were sure had occurred.

  There was little interest, then, in the scientific justifications of the USGS volcanologists who had “attacked” their town and their livelihood, and there was little enthusiasm for listening to the carefully structured two days of presentations planned for this meeting—presentations
designed to show why Dr. Roy Bailey and Dr. Alan Ryall and many others felt Mammoth was possibly sitting on a reawakening volcano in a preemptive phase. (It was startling enough for the townspeople to hear that for all the years they had been there, they had been living inside a volcanic caldera!)

  But the evidence was there—had been there—and would continue to be there. And it had started with the scientists’ puzzlement over the four moderate quakes which had struck Mammoth two years before on May 25, 1980, seven days after the explosion of Mount St. Helens eight hundred miles to the northwest—quakes which heavily damaged only three buildings (including the high school) in a community largely consisting of wood-frame buildings which tolerate seismic waves quite well.

  Dr. Roy Bailey had been studying the Long Valley caldera for years, and had published a paper on the volcanic activity and history of the area in 1975. It had been only a decade since scientists had first recognized the fact that Long Valley was an ancient caldera from a seven-hundred-thousand-year-old cataclysm, and even later that they discovered the widespread evidence of a still-active magma chamber beneath the valley floor.

  But Bailey was also aware that Long Valley lies on a very active fault zone which runs the length of the eastern front of the Sierra Nevada range. Just to the south of the caldera, in Owens Valley, one of the three largest earthquakes in California’s recorded human history occurred in 1872—a great quake which probably registered Ms 8.2 in magnitude. Even longtime residents of Mammoth were used to constant tremors and seismic rumblings from barely felt quakes to “pretty good shakers.” It was assumed by many geologists that the continuing uplift of the Sierras (which were rising continuously in altitude by tiny increments each year) caused the periodic tremors, and the occasional large quakes. Therefore, the reasoning went, the quakes of May 1980 were probably more of the same: tectonic in origin.