VOLCANOES AND ERUPTIONS
Politicians and Volcanoes
It was a coincidence of geography. On May 8, 1902, the beautiful city of St. Pierre, Martinique, known as the Paris of the Caribbean, happened to be in the killing path of a searingly hot volcanic hurricane that swept down the flank of Mount Pelee and killed 29,000 people. And it was a circumstance of timing that the city was in the process of election campaigning. It was an atmosphere doubly charged with election politics and a volcano that had been acting up for a couple of months. People were ambivalent about leaving: on the one hand, they wanted to support their candidate, but on the other, the explosions, rumblings, and sulfurous smell of the volcano frightened many, some of whom chose to leave the area. And yet, there were some curious people who came to St. Pierre from other towns and villages to watch the eruption. In 1902 volcanologists had a very rudimentary knowledge about volcanic processes and did not know that volcanic hurricanes (pyroclastic flows: pyro = "fire"; clastic = "broken") existed. Hence this eruption made Mount Pelee the greatest killer volcano of the twentieth century. If the precatastrophic volcanic activity then shown by Mount Pelee were to occur today, modern volcanologists, having gained ninety years of cumulative experience since the 1902 eruption, would very likely urge immediate evacuation of the city regardless of other circumstances.
Gaston Landes, a professor at the high school in St. Pierre in 1902, said that ash and the sulfur smell from Mount Pelee would not cause great damage, and if the volcano erupted lava flows, they could not reach the city because too many ridges and valleys stood in the way. He was right about the lava flows, but he did not know about hot pyroclastic flows. He gave assurances that little damage would occur even with a big eruption. But on May 8 at 8:03 A.M. the most explosive eruption began, and within five minutes the pyroclastic flow swept through St. Pierre, blowing away, burying, and burning buildings and people. Those not killed outright by physical force died by inhaling ash, which clogged their nasal passages and trachea, and searing gases, which scorched their lungs (figs. 1-1 and 1-2).
The eruption of Mount Pelee drew the world's attention to the existence of pyroclastic flows and started a line of research that is still continuing (see chap. 5). Since 1902, volcanologists have gathered considerable information about the behavior of volcanoes. They now have instruments to detect the small swellings of a volcano that indicate molten rock (magma) is rising into the edifice of the volcano. Seismologists, using seismographs, can find the origin of an earthquake (the focus) below a volcano and pinpoint the depth at which magma is stirring. Gases that originate from magma and reach the surface can be analyzed. One of these gases is sulfur dioxide, which indicates that live magma is moving upward through the volcano and may erupt. The presence of older rock fragments within the exploded debris suggests that the explosions are caused by groundwater that flashes to steam from the heat of the underlying magma and blasts apart preexisting solid rock. The presence of newly solidified pieces of magma suggests that magma could be approaching the surface.
Knowledge of volcanic behavior gained during the twentieth century was used by volcanologists at Mount St. Helens in 1980 to warn of impending danger, but as with Mount Pelee, volcanologists still did not have enough information to predict with certainty how Mount St. Helens was going to behave.
A Modern Tragedy: Mount St. Helens
On March 25, 1980, a group of geology students and three professors (including one of the authors--RVF) from a class in volcanology at the University of California at Santa Barbara visited the Hawaii Volcanological Observatory. We went to the wrong place to witness the beginning of an eruption, for on March 27, Mount St. Helens would erupt. But we did learn from an excited seismologist at the observatory that an earthquake of magnitude 4.1 had occurred beneath Mount St. Helens in southern Washington on March 20, ending the volcano's 123-year rest. Other earthquakes at Mount St. Helens before March 27 had caused cracks to appear in its summit glaciers. Had we gone to the chain of volcanoes that forms the backbone of the Cascade Mountains instead of to Hawaii, we would have witnessed the modest beginnings of one of the most highly publicized and intensely studied eruptions of the twentieth century. Then, on May 18, 1980, nearly two months after the first stirrings of Mount St. Helens, the volcano turned violent.
An Eruption Carnival Turned Tragic
Mount St. Helens was center stage and people came for the show. During the interval prior to its climactic eruption--from March 20 to May 17, 1980--the volcano entertained the public. Mount St. Helens' antics and its potential for danger drew people from everywhere. Entrepreneurs sold T-shirts, cups, posters, and bric-a-brac labeled with humorous slogans and cartoons (fig. 1-3). The main evacuation artery north of Mount St. Helens, Washington State Highway 504, was jammed with sightseers, there to witness the first eruption in the lower forty-eight states since Mount Lassen erupted in 1914. Some people said they came to see the "big one." Cups of coffee and snacks were sold by the thousands. Roadblocks challenged some of the spectators, who then broke them down or snuck around them. State officials set up a "red zone" around Mount St. Helens to keep people from possible harm should there be an eruption (fig. 1-4); however there were not enough personnel to monitor the roadblocks twenty-four hours a day. The activity of the volcano excited people, and they wanted to see it. But at 8:32 A.M., May 18, 1980, the carnival turned tragic with a violent eruption. Many people, some on official business, died within the red zone. Volcano watchers, as well as campers thought to be in safe zones and out of sight of the volcano, were also caught in the doomed area.
On the quiet, sunny morning of May 18, Charles McNerney, John Smart, and several other people had found their way to an overlook to watch Mount St. Helens, just in case it erupted. They had a good view of the volcano from a cleared area along the North Toutle River near Castle Lake, 13 kilometers (see appendix 2) west of the volcano. At 8:32 A.M., the volcano watchers got their wish. It was much deadlier than they could have dreamed, for the north side of the volcano collapsed. Then came the blast. A black cloud came directly from the summit and within seconds climbed over a ridge toward them. A warm wind began blowing ahead of the cloud and increased until trees bent over and branches broke; the approaching blast must have pushed air in front of it. The events of the first two minutes after the eruption were warning enough for McNerney and Smart to leave. The other people may have decided to leave a minute or two later, but it would have been too late because even McNerney and Smart barely escaped with their lives. They drove as fast as they could (up to 125 kilometers per hour on straight stretches) down a dirt road toward Highway 504 but the cloud was gaining on them. They felt the radiant heat of the cloud carried by the wind that blew into the car through the open sunroof. It felt like the car's heater was on. After reaching the paved Highway 154, they accelerated to 140 kilometers per hour on some stretches and finally began to outdistance the cloud. When they lost sight of it, they stopped in relief, hoping that it, too, had stopped; but it soon reappeared, moving at about 72 kilometers per hour. The base of the cloud looked to them like an avalanche of black chalk dust. First, one part of the cloud shot out in front, then another, then another, like waves lapping onto a beach. What they were seeing was the turbulent front of a deadly pyroclastic flow. After pulling back onto the highway, they finally outran the cloud, at an average speed of 105 kilometers per hour.
Early that morning, James Scymanky and three others were cutting wood in the valley of Hoffstadt Creek, 20 kilometers away from, and completely out of sight of, Mount St. Helens. Showing little concern about the volcano, Scymanky and two other men were felling small trees with chainsaws when a fourth man shouted that he saw a cloud appear over the ridge. Within about ten seconds came a thunderous crashing, crunching, and grinding sound from the east as trees were felled by of the blast. The men were soon engulfed by the blast cloud. The force knocked Scymanky down, and he felt a searing, painful heat on his back that lasted about two minutes. When visibility returned, the forest of small trees lay upon the ground throughout the entire valley, which was covered with 25 centimeters of gray ash. The men's clothing remained intact, but their bodies had been extensively burned. Scymanky's lungs were not fatally seared, and he somehow survived his burns, but the others subsequently died from theirs.
The explosion from Mount St. Helens fanned outward on the ground from the volcano in the pattern of a half circle. It had occurred as a blast that moved faster and more forcefully northward than eastward or westward. From eyewitness accounts, estimates of the cloud's northerly velocity ranged from 496 to 510 kilometers per hour for a distance of 13 kilometers. Four parties of campers had settled near the northern boundary of destruction. They were not volcano watchers and had not camped where they could see the volcano. They were also separated from it by one or two 300-meter-high ridges. Three of these people, Dale and Leslie Davis and Albert Brooks, had stalled their pickup truck while trying to escape and the blast cloud overran them. It looked to them like a "boiling mass of rock" that picked up trees and threw them into the air. Darkness descended as the cloud surrounded them, and it became very hot in the truck cab. Chunks of rock and wood pounded the truck for a short time but, except for a small vent on the right side of the truck, the windows did not break. One of the trio received burns on both legs, just above the ankles, as ash entered the truck through the broken vent window. A brief period of light appeared a few minutes after the blast first descended upon them, but then ash fell again so densely that they could not see the truck's hood. Nearly a half hour later, at 9 A.M., they decided to abandon the vehicle and walk, even though the darkness required that they use a flashlight. By 10:20 A.M. murky ash still kept visibility at about 10 meters. It wasn't until later that day, after the sky had cleared, that they were rescued by helicopter.
Later examination of the truck showed that heat had deformed its plastic grill and had melted a styrofoam cooler in the truck bed. The vehicle's right side, which had faced the volcano, had been extensively damaged--the blast had stripped its chrome trim and had sandblasted the paint.
In Miners Creek, which was over the ridge from the pickup truck, Edward Smith and his companions had tipped an external-frame tent on its side to dry out. A little after 8:32 A.M., several gusts of wind suddenly blew the tent over and were immediately followed by what sounded like three distant rifle shots. Ten to fifteen seconds later, a black cloud shot overhead, and rocks as big as golf balls began to fall. The sky became dark, and ash fell so heavily that visibility was no more than about a half a meter, even by the light of a flashlight. Although thousands of trees fell, Smith and his friends did not hear them, nor did they feel a blast or wind at that time. The first material to fall on them was cold, but shortly thereafter, the air became uncomfortably hot, as if a forest fire were nearby, but the heat did not last very long.
Two other groups were camped along the north bank of the Green River about 22 kilometers north of the volcano and across two 300-meter-high ridges, certainly a safe distance from Mount St. Helens, or so everybody thought, even the volcanologists. One of the groups included Bruce Nelson, Sue Ruff, Terry Crall, and Karen Varner. Nelson and Ruff told of a wind that preceded the blast cloud by ten to fifteen seconds, strong enough to blow flames horizontally outward from the campfire, but not strong enough to impede a person's movement or to blow down trees. The campers heard no loud noises prior to the cloud's arrival, but when it did arrive, daylight turned to darkness and all of the trees seemed to topple over simultaneously. In the confusion, Nelson and Ruff accidentally fell into a hole left by the root ball of a blown-over tree and were protected from other falling trees. They could hear one another while in the hole, but it was too dark to see. After they had been in the hole about ten seconds, the temperature increased enough to singe their hair, which they could hear sizzle. (Hair singes at 120 [degrees] C.) Bruce Nelson, a baker familiar with ovens, estimated the temperature to be about 300 [degrees] F. The heat was intense enough to boil pitch from the trees and still cause minor burns several minutes later. After a few minutes of darkness, the sky suddenly cleared for a few minutes and then a dense fall of ash began. After Nelson and Ruff had dug themselves out of the debris, they called for Crall and Varner but received no answer--they had been killed by falling trees. Close by were two other campers, Dan Balch and Bryan Thomas. A tree fell on Bryan Thomas and broke his hip, but he was too heavy to carry, so Nelson, Ruff, and Balch built him a lean-to for shelter and set out on foot. Balch, who was barefoot, could not walk through the hot ash and was also left behind. Nelson and Ruff continued and during their trek encountered Grant Christensen, whose pickup truck would not start. After about three hours, the three sighted a helicopter, which they signaled by using their clothes to stir up dust. The three men, together with Balch and Thomas, were rescued that day by helicopter.
Mike and Lu Moore, from the town of Castle Rock, were camped near the Green River at a point 20 kilometers from the volcano with their daughters, four-year-old Bonnie Lu and three-month-old Terra. They had parked and then hiked a 4-kilometer-long trail to spend Saturday night at a campsite intending to return to Castle Rock on Sunday afternoon. While making breakfast the next morning, Lu Moore noticed a rumbling noise and reported that "it felt like there was an earthquake inside you." The family quickly loaded their backpacks and moved to a shelter for hunters. According to Mike Moore, "You could physically see the cloud of ash moving toward us. It was the blackest cloud I had ever seen" (Daily News, Volcano, p. 61). Thunder and lightning accompanied the cloud, which passed over them, and it turned very dark as ash began to fall. So much ash rained down that the Moores had to breathe through stockings to filter it out. Within an hour or two, when the darkness had lifted, they wanted to return to their car but were blocked by fallen trees. They spent Sunday night in their tent and were rescued Monday morning by a helicopter. The Moore family had been just outside of the devastation boundary. Before the blast cloud reached them, it had risen from the ground and lofted over their heads, so rather than being overwhelmed by the hurricane-like cloud moving laterally across the ground, they were showered by ash.
Venus Dergan and Roald Reitan, who were camped alongside the Toutle River, woke up as the river began to rampage. As the water rose and they began throwing their belongings into the car, Reitan saw a huge logjam that was being held back by part of a railroad bridge. The water rose swiftly and they climbed to the top of their car, but the rising water swept the vehicle down a steep embankment and they had to jump off. Dergan was then sucked under, and when Reitan located her, he could only see her nose between two logs. Reitan reached her by pulling himself along one of the logs. He then grabbed her by the hair and pulled her to the surface. They somehow managed to reach the edge of the flood and ran in knee-deep muddy water to reach a road. Fearing that the water would soon wash out the road, they climbed up a steep hillside and escaped.
In the final count at Mount St. Helens, thirty-five people were confirmed dead and twenty-two more were never found. One hundred and thirteen people were rescued by helicopters on the day of the eruption, and within the first few days, rescuers had found a total of one hundred and twenty-eight survivors. Fifty-three people were found within 1.6 kilometers outside of the blast boundary. Forty-seven were rescued from the south side of the volcano, where there was neither a blast surge nor a heavy ash fall. Eleven survivors were just inside the blast-zone boundary. Of these, six were unharmed, two inside a vehicle had second-degree burns, two endured third-degree burns, and one suffered a fracture.
Autopsies of seventeen victims showed that they had died from asphyxiation by inhaled ash. Two victims died from a tree that fell on their tent. Another, parked in his automobile 16 kilometers from the volcano, died when he was hit by a rock that flew through the car window. The skin of many of the dead was mummified with dark discoloration, and exposed muscles were cooked rather than desiccated. Hair was singed on victims found as far as 18 kilometers from the volcano, and burns accounted for three deaths that occurred 15 kilometers from the summit. Burning, singeing and mummification were caused by the heat of the blast cloud.
Temperatures of the blast cloud were estimated by the effects of the heat on vehicles, trees, and buried wood. The most revealing effects were on plastics composing the turn-signal lights, tail lights, and instrument panels of the cars and trucks. To determine melting temperatures, similar materials were obtained from vehicles of the same type and year of manufacture and were exposed to heat. Estimates ranged from 100 [degrees] to 300 [degrees] C, yet some people survived because the hottest part of the blast cloud had moved swiftly by. The blast cloud from Mount St. Helens was relatively cool compared with many pyroclastic flows, which can attain 850 [degrees] C or more.
Another peril stemming from the eruption was the lahars (mudflows; see chap. 6) that originated in three different ways at Mount St. Helens:
* Water within the pores of rocks of the original volcano, which collapsed to become an avalanche, was squeezed from the pores of the avalanche by its own weight after it had stopped. The water that oozed out of the stationary avalanche deposit ran from its surface in rivulets that coalesced into bigger and bigger lahars that raced down the North Fork Toutle River.
* Some lahars were fed with water from snow melted by hot pyroclastic flows.
* Pyroclastic flows plunged into the streams and rivers and mixed with the water to form thick mud that moved downstream as lahars.
Lahars from these diverse origins mixed at tributary junctions to create increasingly larger lahars. As they mixed with stream water, they became more dilute and turned into floods that carried enormous loads of ash down the canyons draining the volcano and then into the tributaries of the Columbia River. The floods took as many as six lives and caused millions of dollars in property damage as they swept down the north and south forks of the Toutle River (fig. 1-5). And so much ash was transported to the Columbia River that it became too shallow for ships sailing from the Pacific Ocean to the Port of Portland. Ship traffic was completely stopped for a week and then restricted for three months while the ashy muck was dredged from the river. The flooding also damaged port facilities along the Columbia River at Longview and Kelso, Washington, and automobile, truck, and railroad traffic between Seattle and Portland was interrupted by flooding and damage to bridges.
Far from the Volcano
The eruption's impact was not as immediately dramatic far from the volcano as it was in the blast zone, but it caused serious social and economic disruption across eastern Washington, Idaho, and Montana--a populated area in contrast with the wilderness around Mount St. Helens. In eastern Washington, 152 million cubic meters of volcanic ash fell like snow upon the cities and towns and millions of acres of agricultural land. Almost 50 percent of Washington State felt the greatest impact from the various effects of the volcano. More than 4 centimeters of ash fell on Ritzville, 275 kilometers from the volcano, but only 1.5 centimeters fell on Yakima, 135 kilometers northeast of Mount St. Helens. Low-level winds apparently deposited ash on Yakima, but the eruption cloud that penetrated high into the atmosphere rained down most heavily in the Ritzville area. Spokane, 410 kilometers away, received about 0.5 centimeter of the talcum-powder-like volcanic dust. Farther across the United States, the highly dispersed and fine-grained ash was not recognized by those unaware that dust from Mount St. Helens was in the air (fig. 1-6).
Although the layer of ash was thin, it was enough to disrupt power, communication, and transportation systems across eastern Washington. Airports and highways were closed for up to a week. Where rain had fallen, electrical transmission facilities discharged as a result of arcing across the power-line insulators that were coated with wet ash. Because of darkness and unexpectedly cold daytime temperatures, power usage by residents who were turning on lights and heaters taxed generating plants. Telephone services became overloaded by concerned people calling neighbors and friends.
It was soon discovered that shoveling volcanic ash was not like shoveling snow. The ash was hard to handle: as a dry powder, it was exceedingly difficult to contain on shovels, and as a wet mixture, it was much heavier than snow. Because the ash did not melt, it had to be removed and places found to dump it, all of which added to the cost of disposal.
The ashfall from Mount St. Helens was relatively small in volume when compared with that from truly large eruptions, but the problems that modern society faces from even a relatively small ashfall are illustrated by the experience of Yakima (pop. 50,000). The ash cloud first reached the city at about 10:00 A.M., an hour and a half after the blast. Lightning and thunder accompanied the dark cloud. Cars stalled, motors and generators stopped running, and the city was silent and dark for sixteen hours. An estimated 546 million kilograms of ash fell on Yakima, with nearly 14.5 million blanketing airport runways. All highways and the Yakima airport were closed, and the city was isolated. The tiny, sharp glassy ash particles choked air filters and abraded bearings in wheels and motors. Indoors, dusting the ash off furniture left scratches that looked as though they had been caused by kitchen cleanser.
Yakima had no planned volcano emergency procedures or experience with ashfalls. Local and state officials tried to contact emergency services for information, but the offices were unprepared for ashfall problems. The Emergency Broadcast System, known to dedicated radio listeners throughout the United States, did not provide a warning because the Sunday-morning staff did not know how to operate the equipment. The air was dusty and murky, roads were closed, and there were no buses, planes, or trains available. Mail deliveries and refuse collection would not resume on Monday, nor would the schools open. The sewage treatment plant became clogged with ash and could not operate. Despite the threat of disease, raw sewage had to be discharged into the Yakima River. A local radio station that furnished twenty-four-hour news proved to be the most useful medium for disseminating information.
It quickly became evident that equipment and manpower were inadequate to clean up the city and that outside help was needed. The entire cleanup eventually required ten times more money than was needed for usual maintenance. The costs were also indirect. During the cleanup, Yakima had to suspend business activity. The central business district was closed for two and one half days while streets, alleys, sidewalks, parking lots, and roofs were swept and shoveled clean of ash. Any modern city downwind from active volcanoes needs to study the Yakima experience. Only 1.5 centimeters of ash fell upon the city, but the problems and costs were enormous, and these problems multiply geometrically with increasing ash thickness.
The Costs of the Eruption
The $2.7 billion in damages caused by the eruption of Mount St. Helens affected all of the taxpayers in the state of Washington, and in one way or another, in the entire nation. Short-term losses to Washington State cost as much as $970 million. Over half of the losses were timber resources. Cleanup costs were another $270 million, and $85 million was spent to restore damaged property (roads, bridges, and other property in the blast zone and flooded areas). Agricultural losses were estimated at $40 million. Twenty-seven bridges and 272 kilometers of roads had to be replaced. Sixty-one houses were totally destroyed, fifty-five were heavily damaged, and sixty-four were isolated by mudflows along the Toutle River. Two-thirds of the cleanup costs went to areas near the volcano and downstream to the Columbia River. Substantial funds went to dredging the Toutle, Cowlitz, and Columbia Rivers.
The Eruption Setting
Mount St. Helens straddles Cowlitz and Skamania Counties, is bordered on the north by Lewis County, and lies within the U.S. Forest Service's Gifford Pinchot National Forest of southern Washington. The Green River drains the area north of the volcano, the South Fork and North Fork of the Toutle River drain its western side, and the Lewis River--along which there are three dams that form Lake Merwin, Yale Lake, and Swift Reservoir--drains the southern side of the mountain. Their waters flow into the Columbia River and on to the Pacific Ocean.
Before the eruption, Mount St. Helens was one of the premier outdoor playgrounds in the state of Washington, being easily accessible to the major population centers of Portland and Seattle. The once graceful conical shape loomed high over Spirit Lake, whose shoreline was dotted with organization camps and resorts. The area was an outdoor paradise for fishing, camping, hiking, skiing, and hunting. The land north of the volcano harbored many small fishing lakes and was graced by old-growth Douglas fir, hemlock, and noble fir. Crusty Harry Truman, in his eighties, owned and ran a resort on the south side of the lake nearest the volcano. It was a land of timber, the largest active company in the area being the Weyerhaeuser Company, with headquarters at Longview, Washington.
In addition to land held by the Gifford Pinchot National Forest, Mount St. Helens and the surrounding land was owned by a variety of private and government concerns. The western volcano margin was owned principally by the Weyerhaeuser Company, its closest border about 5 kilometers away from the volcano. On the mountain and to the north, alternate sections of land were owned primarily by Weyerhaeuser, the Burlington Northern Railroad, and the Washington Department of Natural Resources. There were also a number of private mining claims dating back to the turn of the century. The volcano was in the jurisdiction of the U.S. Forest Service, but there was much land owned privately, as well as by Cowlitz and Skamania Counties and by the state of Washington.
It was in this wondrous natural playground that the Mount St. Helens eruption began so inauspiciously on March 20, 1980, and erupted so violently on May 18.
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