REPORT:
Eruptions of Mount St. Helens: Past, Present, and Future

MSH82_st_helens_spirit_lake_reflection_05-19-82.jpg Mount St. Helens and the devastated area is now within the 110,000-acre Mount St. Helens National Volcanic Monument, under jurisdiction of the United States Forest Service. Visitor centers, interpretive areas, and trails are being established as thousands of tourists, students, and scientists visit the monument daily. Mount St. Helens is once again considered to be one of the most beautiful and interesting of the Cascade volcanic peaks. USGS Photograph taken on May 19, 1982, by Lyn Topinka. [medium size] ... [large size] ... [TIF Format, 18 M]

The cataclysmic eruption and related events May 18 rank among the most significant geologic events in the United States during the 20th century. The processes, effects, and products of the chain of events were the most intensively studied and photographically documented of any explosive volcanic eruption in the world to date. The wealth of data on Mount St. Helens before, during, and after the May 18 eruption enabled geoscientists of the U.S. Geological Survey (USGS), the University of Washington, and other research institutions in the United States and abroad to put into perspective the devastating impact of suddenly unleashed volcanic energy.

In 1981 and 1982, the results of many of these studies were published by the USGS in two comprehensive volumes, Professional Papers 1249 and 1250, both dedicated to the memory of David A. Johnston, a USGS volcanologist killed while making scientific observations on May 18. Intermittently active through the 1980s, Mount St. Helens continues to receive intensive study. This booklet-updated and revised from the first edition (1984) on occasion of the 10th anniversary of the May 18, 1980, eruption-presents selected highlights of the volcano's eruptive history, reviews its activity in the past decade, and speculates about its possible future behavior. Materials cited in the Selected Readings provide more detailed information on topics that have been omitted or treated only briefly.

[Map,18K,InlineGIF] The active and potentially active volcanoes of the principal part of the Cascade Range of the Pacific Northwest. The Cascade Range extends north into British Columbia (not shown on map). -- Modified from original by Lyn Topinka, 1997

Geologists call Mount St. Helens a composite volcano (or stratovolcano), a term for steep-sided, often symmetrical cones constructed of alternating layers of lava flows, ash, and other volcanic debris. Composite volcanoes tend to erupt explosively and pose considerable danger to nearby life and property. In contrast, the gently sloping shield volcanoes, such as those in Hawaii, typically erupt nonexplosively, producing fluid lavas that can flow great distances from the active vents. Although Hawaiian-type eruptions may destroy property, they rarely cause death or injury.

Before 1980, snow-capped, gracefully symmetrical Mount St. Helens was known as the "Fujiyama of America." Mount St. Helens, other active Cascade volcanoes, and those of Alaska comprise the North American segment of the circum-Pacific "Ring of Fire," a notorious zone that produces frequent, often destructive, earthquake and volcanic activity.

MSH80_st_helens_from_johnston_ridge_05-17-80.jpg Mount St. Helens on May 17, 1980, one day before the devastating eruption. The view is from Johnston's Ridge, six miles (10 kilometers) northwest of the volcano. USGS Photograph taken on May 17, 1980, by Harry Glicken. [medium size] ... [large size]

Some Indians of the Pacific Northwest variously called Mount St. Helens "Louwala-Clough," or "smoking mountain." The modern name, Mount St. Helens, was given to the volcanic peak in 1792 by Captain George Vancouver of the British Royal Navy, a seafarer and explorer. He named it in honor of a fellow countryman, Alleyne Fitzherbert, who held the title Baron St. Helens and who was at the time the British Ambassador to Spain. Vancouver also named three other voicanoes in the Cascades- Mounts Baker, Hood, and Rainier-for British naval officers.

The local Indians and early settlers in the then sparsely populated region witnessed the occasional violent outbursts of Mount St. Helens. The volcano was particularly restless in the mid-19th century, when it was intermittently active for at least a 26-year span from 1831 to 1857. Some scientists suspect that Mount St. Helens also was active sporadically during the three decades before 1831, including a major explosive eruption in 1800. Although minor steam explosions may have occurred in 1898, 1903, and 1921, the mountain gave little or no evidence of being a volcanic hazard for more than a century after 1857. Consequently, the majority of 20th-century residents and visitors thought of Mount St. Helens not as a menace, but as a serene, beautiful mountain playground teeming with wildlife and available for leisure activities throughout the year. At the base of the volcano's northern flank, Spirit Lake, with its clear, refreshing water and wooded shores, was especially popular as a recreational area for hiking, camping, fishing, swimming and boating.

The tranquility of the Mount St. Helens region was shattered in the spring of 1980, however, when the volcano stirred from its long repose, shook, swelled, and exploded back to life. The local people rediscovered that they had an active volcano in their midst, and millions of people in North America were reminded that the active-and potentially dangerous- volcanoes of the United States are not restricted to Alaska and Hawaii.

[Map,31K,GIF] Sketch map showing the location of Mount St. Helens and the principal drainages and places mentione in the text. -- Modified from original by Lyn Topinka, 1997, 2002

Ancestral Mount St. Helens began to grow before the last major glaciation of the Ice Age had ended about 10,000 years ago. The oldest ash deposits were erupted at least 40,000 years ago onto an eroded surface of still older volcanic and sedimentary rocks. Intermittent volcanism continued after the glaciers disappeared, and nine main pulses of pre-1980 volcanic activity have been recognized. These pulses lasted from about 5,000 years to less than 100 years each and were separated by dormant intervals of about 15,000 years to only 200 years. A forerunner of Spirit Lake was born about 3,500 years ago, or possibly earlier, when eruption debris formed a natural dam across the valley of the North Fork of the Toutle River. The most recent of the pre-1980 eruptive activity began in A.D. 1800 with an explosive eruption, followed by several additional minor explosions and extrusions of lava, and ended with the formation of the Goat Rocks lava dome by 1857.

[Graphic,14K,GIF] The post-A.D. 1400 segment of the 50,000-year eruptive history of Mount St. Helens (after USGS Bulletin 1383-C).

Mount St. Helens is the youngest of the major Cascade volcanoes, in the sense that its visible cone was entirely formed during the past 2,200 years, well after the melting of the last of the Ice Age glaciers about 10,000 years ago. Mount St. Helens' smooth, symmetrical slopes are little affected by erosion as compared with its older, more glacially scarred neighbors - Mount Rainier and Mount Adams in Washington, and Mount Hood in Oregon. As geologic studies progressed and the eruptive history of Mount St. Helens became better known, scientists became increasingly concerned about possible renewed eruptions. The late William T. Pecora, a former Director of the USGS, was quoted in a May 10, 1968, newspaper article in the Christian Science Monitor as being "especially worried about snow-covered Mt. St. Helens."

On the basis of its youth and its high frequency of eruptions over the past 4,000 years, Crandell, Mullineaux, and their colleague Meyer Rubin published in February 1975 that Mount St. Helens was most likely to reawaken and to erupt "perhaps before the end of this century." This prophetic conclusion was followed in 1978 by a more detailed report, in which Crandell and Mullineaux elaborated their earlier conclusion and analyzed, with maps and scenarios, the kinds, magnitudes, and areal extents of potential volcanic hazards that might be expected from future eruptions of Mount St. Helens. Collectively, these two publications contain one of the most accurate forecasts of a violent geologic event.

A magnitude 4.2 (Richter Scale) earthquake on March 20, 1980, at 3:47 p.m. Pacific Standard Time (PST), preceded by several much smaller earthquakes beginning as early as March 16, was the first substantial indication of Mount St. Helens' awakening from its 123-year sleep. Earthquake activity increased during the following week, gradually at first and then rather dramatically at about noon on March 25. The number of earthquakes recorded daily reached peak levels in the next 2 days, during which 174 shocks with magnitudes greater than 2.6 were recorded. Many hundreds of smaller earthquakes accompanied these larger events, the largest of which were felt by people living close to the volcano. Aerial observations of Mount St. Helens during the week of seismic buildup revealed small earthquake-induced avalanches of snow and ice, but no sign of an eruption.

With a thunderous explosion, or possibly two nearly simultaneous ones, widely heard in the region at about 12:36 p.m. PST on March 27, Mount St. Helens began to spew ash and steam, marking the first significant eruption in the conterminous United States since that of Lassen Peak, California, from 1914 to 1917. The crown of the ash column rose to about 6,000 feet above the volcano. The initial explosions formed a 250-foot-wide crater within the larger, preexisting snow- and ice-filled summit crater, and new fractures broke across the summit area.

MSH80_crater_first_day_from_north_03-27-80.jpg Mount St. Helens' eruption, first crater, from the north. USGS Photograph taken on March 27, 1980, by David Frank. [medium size] ... [large size]

Through April 21, Mount St. Helens intermittently ejected ash and steam in bursts lasting from a few seconds to several tens of minutes. The first crater was joined on the west by a second, slightly larger crater, and as the activity continued, both craters enlarged and ultimately merged. Several avalanches of snow and ice, darkened by ash, formed prominent streaks down the mountain's slopes. The effect of the prevailing easterly wind was striking during the March-April eruptive activity, transforming the snow-covered Mount St. Helens into a "two-tone" mountain.

MSH80_ash_covered_st_helens_from_southwest_03-30-80_bw.jpg Ash-covered Mount St. Helens, view from the southwest. USGS Photograph taken on March 30, 1980, by C.Dan Miller. [medium size] ... [large size]

The ash blown out between March 27 and May 18 was derived entirely from the 350-year-old summit dome, shattered and pulverized by phreatic (steam-blast) processes driven by the explosively expanding, high-temperature steam and other gases. No magma (molten rock and contained gases) was tapped during the initial eruptions.

Intense earthquake activity persisted at the volcano during and between visible eruptive activity. As early as March 31, seismographs also began recording occasional spasms of volcanic tremor, a type of continuous, rhythmic ground shaking different from the discrete sharp jolts characteristic of earthquakes. Such continuous ground vibrations, commonly associated with eruptions at volcanoes in Hawaii, Iceland, Japan, and elsewhere, are interpreted to reflect subsurface movement of fluids, either gas or magma. The combination of sustained strong earthquake activity and volcanic tremor at Mount St. Helens suggested to scientists that magma and associated gases were on the move within the volcano, thereby increasing the probability of magma eruption.

Visible eruptive activity ceased temporarily in late April and early May. Small steam-blast eruptions resumed on May 7, continued intermittently for the next several days, and ceased again by May 16. During this interval, the forceful intrusion of magma into the volcano continued with no respite, as was shown by intense seismic activity and visible swelling and cracking of the volcano. The swelling was easily measurable and affected a large area on the north face of Mount St. Helens; this area became known as the "bulge," the initial growth of which probably began during the first eruption (March 27) or perhaps even a few days before. Through mid-May about 10,000 earthquakes were recorded. The earthquake activity was concentrated in a small zone less than 1.6 miles directly beneath the bulge on the north flank of Mount St. Helens.

A comparison of aerial photographs taken in the summer of 1979 with those taken during and after April 1980 showed that by May 12 certain parts of the bulge near the summit were more than 450 feet higher than before the magma intrusion began. Repeated measurements begun in late April with precise electronic instruments that shoot a laser beam to reflector targets placed on and around the bulge showed that it was growing northward at an astonishing rate of about 5 feet per day. The movement was predominantly horizontal-clear evidence that the bulge was not simply slipping down the volcano's steep slope. As the bulge moved northward, the summit area behind it progressively sank, forming a complex down-dropped block called a graben. These changes in the volcano's shape were related to the overall deformation that increased the volume of the mountain by 0.03 cubic mile by mid-May. This volume increase presumably corresponded to the volume of magma that pushed into the volcano and deformed its surface. Because the intruded magma remained below ground and was not directly visible, it was called a cryptodome, in contrast to a true volcanic dome exposed at the surface.

MSH80_bulge_on_north_side_04-27-80.jpg A "bulge" developed on the north side of Mount St. Helens as magma pushed up within the peak. Angle and slope-distance measurements to the bulge indicated it was growing at a rate of up to five feet (1.5 meters) per day. By May 17, part of the volcano's north side had been pushed upwards and outwards over 450 feet (135 meters). The view is from the northeast. USGS Photograph taken on April 27, 1980, by Peter Lipman. [medium size] ... [large size]

In summary, during late March to mid-May 1980, Mount St. Helens was shaken by hundreds of earthquakes, intermittently erupted ash and debris derived by steam blast reaming out of its preexisting summit dome, and experienced extremely large and rapid deformation caused by magma intrusion. The hot intruding magma provided the thermal energy to heat groundwater, which explosively flashed to generate and sustain the observed steam-blast eruptions. For 2 months the volcano was literally being wedged apart, creating a highly unstable and dangerous situation. The eventual collapse of the bulge on the north flank triggered the chain of catastrophic events that took place on May 18, 1980.

Debris Avalanche

"noticed landsliding of rock and ice debris 
 in-ward into the crater... the south-facing wall 
 of the north side of the main crater was especially 
 active. Within a matter of seconds, perhaps 15 seconds, 
 the whole north side of the summit crater began to 
 move instantaneously. ... The nature of movement
 was eerie.... The entire mass began to ripple and 
 churn up, without moving laterally. Then the entire 
 north side of the summit began sliding to the north 
 along a deep-seated slide plane. I (Keith Stoffel) 
 was amazed and excited with the realization that
 we were watching this landslide of unbelievable 
 proportions. ... We took pictures of this slide 
 sequence occurring, but before we could snap off 
 more than a few pictures, a huge explosion blasted 
 out of the detachment plane. We neither felt nor 
 heard a thing, even though we were just east of the 
 summit at this time."

Realizing their dangerous situation, the pilot put the plane into a steep dive to gain speed, and thus was able to outrun the rapidly mushrooming eruption cloud that threatened to engulf them. The Stoffels were fortunate to escape, and other scientists were fortunate to have their eyewitness account to help unscramble the sequence and timing of the quick succession of events that initiated the May 18 eruption.

The collapse of the north flank produced the largest landslide-debris avalanche recorded in historic time. Detailed analysis of photographs and other data shows that an estimated 7-20 seconds (about 10 seconds seems most reasonable) elapsed between the triggering earthquake and the onset of the flank collapse. During the next 15 seconds, first one large block slid away, then another large block began to move, only to be followed by still another block. The series of slide blocks merged downslope into a gigantic debris avalanche, which moved northward at speeds of 110 to 155 miles an hour¹. Part of the avalanche surged into and across Spirit Lake, but most of it flowed westward into the upper reaches of the North Fork of the Toutle River. At one location, about 4 miles north of the summit, the advancing front of the avalanche still had sufficient momentum to flow over a ridge more than 1,150 feet high. The resulting hummocky avalanche deposit consisted of intermixed volcanic debris, glacial ice, and, possibly, water displaced from Spirit Lake. Covering an area of about 24 square miles, the debris avalanche advanced more than 13 miles down the North Fork of the Toutle River and filled the valley to an average depth of about 150 feet; the total volume of the deposit was about 0.7 cubic mile. The dumping of avalanche debris into Spirit Lake raised its bottom by about 295 feet and its water level by about 200 feet.

[Graphic,100K,InlineGIF] Mount St. Helens May 18, 1980 Eruption Sequence -- Lyn Topinka, 1998; Modified from: Brantley and Topinka, 1984 [Graphic,21K,InlineGIF] Graphic of Mount St. Helens area showing May 18, 1980 devastation.

Lateral Blast

Within a few seconds after the onset and mobilization of the debris avalanche, the climactic eruptions of May 18 began as the sudden unloading of much of the volcano's north flank abruptly released the pent-up pressure of the volcanic system. The sudden removal of the upper part of the volcano by the landslides triggered the almost instantaneous expansion (explosion) of high temperature-high pressure steam present in cracks and voids in the volcano and of gases dissolved in the magma that caused the bulge of the cryptodome. The abrupt pressure release, or "uncorking," of the volcano by the debris avalanche can be compared in some ways to the sudden removal of the cap or a thumb from a vigorously shaken bottle of soda, or to punching a hole in a boiler tank under high pressure.

Although the lateral blast began some seconds later than the debris avalanche, the blast's velocity was much greater, so that it soon overtook the avalanche. Calculations have shown that the blast's initial velocity of about 220 miles an hour quickly increased to about 670 miles an hour. The average velocity did not surpass the speed of sound in the atmosphere (about 735 miles an hour). This observation is consistent with the lack of reports of loud atmospheric shocks or "sonic booms" from nearby observers such as Keith and Dorothy Stoffel in the light plane or survivors on the ground. In some areas near the blast front, however, the velocity may have approached, or even exceeded, the supersonic rate for a few moments.

The blast was widely heard hundreds of miles away in the Pacific Northwest, including parts of British Columbia, Montana, Idaho, and northern California. Yet, in many areas much closer to Mount St. Helens-for example, Portland, Oregon, only 50 miles away-the blast was not heard. Subsequent studies by the Oregon Museum of Science and Industry demonstrated a so-called "quiet zone" around Mount St. Helens, extending radially a few tens of miles, in which the eruption was not heard. The creation of the "quiet zone" and the degree to which the eruption was heard elsewhere depended on the complex response of the eruption sound waves to differences in temperature and air motion of the atmospheric layers and, to a lesser extent, local topography.

The near-supersonic lateral blast, loaded with volcanic debris, caused widespread devastation as far as 19 miles from the volcano. The area affected by the blast can be subdivided into three roughly concentric zones:

(1) Direct blast zone, the innermost zone, averaged about 8 miles in radius, an area in which virtually everything, natural or manmade, was obliterated or carried away. For this reason, this zone also has been called the "tree-removal zone." The flow of the material carried by the blast was not deflected by topographic features in this zone.

(2) Channelized blast zone, an intermediate zone, extended out to distances as far as 19 miles from the volcano, an area in which the flow flattened everything in its path and was channeled to some extent by topography. In this zone, the force and direction of the blast are strikingly demonstrated by the parallel alignment of toppled large trees, broke off at the base of the trunk as if they were blades of grass mown by a scythe. This zone was also known as the "tree-down zone."

(3) Seared zone, also called the "standing dead" zone, the outermost fringe of the impacted area, a zone in which trees remained standing but were singed brown by the hot gases of the blast.

[Graphic,21K,InlineGIF] Graphic of Mount St. Helens area showing May 18, 1980 devastation.

A similar, but narrower and northeast-trending, strong laterally directed explosion occurred at Mount St. Helens about 1,100 years ago. The blast of May 18, 1980, however, traveled at least three times as far as the 1,100-year-old blast. Thus, the occurrence of a lateral blast such as that of May 18 was not the first in Mount St. Helens' history, but its power and resulting destruction were unprecedented. The lateral blast, debris avalanche, and associated mudflows and floods caused most of the casualties and destruction on May 18; the adverse impact of volcanic ash fallout downwind was minor by comparison.

Ash Eruption and Fallout

A strong, vertically directed explosion of ash and steam began very shortly after the lateral blast. The resulting eruptive column rose very quickly. In less than 10 minutes, the ash column reached an altitude of more than 12 miles and began to expand into a characteristic mushroom-shaped ash cloud. Near the volcano, the swirling ash particles in the atmosphere generated lightning, which in turn started many forest fires. As the eruption roared on, the major part of the ash cloud drifted downwind in an east-northeasterly direction, although ash that rose above the high-speed (Jet-stream) winds followed other paths determined by complex wind directions.

MSH80_eruption_mount_st_helens_05-18-80.jpg On May 18, 1980, at 8:32 a.m. Pacific Daylight Time, a magnitude 5.1 earthquake shook Mount St. Helens. The bulge and surrounding area slid away in a gigantic rockslide and debris avalanche, releasing pressure, and triggering a major pumice and ash eruption of the volcano. Thirteen-hundred feet (400 meters) of the peak collapsed or blew outwards. As a result, 24 square miles (62 square kilometers) of valley was filled by a debris avalanche, 250 square miles (650 square kilometers) of recreation, timber, and private lands were damaged by a lateral blast, and an estimated 200 million cubic yards (150 million cubic meters) of material was deposited directly by lahars (volcanic mudflows) into the river channels. Fifty-seven people were killed or are still missing. USGS Photograph taken on May 18, 1980, by Austin Post. [medium size] ... [large size]

Clear skies permitted tracking the advance of the drifting cloud by satellite imagery. Moving at an average speed of about 60 miles an hour, the cloud reached Yakima, Washington, by 9:45 a.m. PDT and Spokane, Washington, by 11:45 a.m. The ash cloud was dense enough to screen out nearly all sunlight, activating darkness-sensitive switches on street lights in Yakima and Spokane. Street lights remained on for the rest of the darkened day, as the eruption continued vigorously for more than 9 hours, pumping ash into the atmosphere and feeding the drifting ash cloud.

The eruptive column fluctuated in height through the day, but the eruption subsided by late afternoon on May 18. By early May 19, the eruption had stopped. By that time, the ash cloud had spread to the central United States. Two days later, even though the ash cloud had become more diffuse, fine ash was detected by systems used to monitor air pollution in several cities of the northeastern United States. Some of the ash drifted around the globe within about 2 weeks. After circling many more times, most of the ash settled to the Earth's surface, but some of the smallest fragments and aerosols remained suspended in the upper atmosphere for years.

MSH80_volcanic_ash_with_helicopter_08-22-80.jpg For weeks volcanic ash covered the landscape around the volcano and for several hundred miles downwind to the east. Noticeable ash fell in eleven states. The total volume of ash (before its compaction by rainfall) was approximately 0.26 cubic mile (1.01 cubic kilometers), or, enough ash to cover a football field to a depth of 150 miles (240 kilometers). In this photograph, a helicopter stirs up ash while trying to land in the devastated area. USGS Photograph taken on August 22, 1980, by Lyn Topinka. [medium size] ... [large size]

Prevailing winds distributed the fallout from the ash cloud over a wide region. Light ash falls were reported in most of the Rocky Mountain States, including northern New Mexico, and fine ash dusted a few scattered areas farther east and northeast of the main path. The heaviest ash deposition occurred in a 60-mile-long swath immediately downwind of the volcano. Another area of thick ash deposition, however, occurred near Ritzville in eastern Washington, about 195 miles from Mount St. Helens, where nearly 2 inches of ash blanketed the ground, more than twice as much as at Yakima, which is only about half as far from the volcano. Scientists believe that this unexpected variation in ash thickness may reflect differences in wind velocity and direction with altitude, fluctuations in the height of the ash column during the 9 hours of activity, the effect of localized clumping of fine ash particles leading to preferential fallout of the large particle clumps.

[Map,14K,GIF] Generalized map shows the distribution of ash fallout within the United States, from the May 18, 1980 eruption

During the 9 hours of vigorous eruptive activity, about 540 million tons of ash fell over an area of more than 22,000 square miles. The total volume of the ash before its compaction by rainfall was about 0.3 cubic mile, equivalent to an area the size of a football field piled about 150 miles high with fluffy ash. The volume of the uncompacted ash is equivalent to about 0.05 cubic mile of solid rock, or only about 7 percent of the amount of material that slid off in the debris avalanche. The eruption of ash also further enlarged the depression formed initially by the debris avalanche and lateral blast, and helped to create a great amphitheater-shaped crater open to the north. This new crater was about 1 mile by 2 miles wide and about 2,100 feet deep from its rim to its lowest point. The area of this crater roughly encompassed that of the former bulge on the north flank of the volcano and the former summit zone. After the eruption, the highest point on the volcano was about 8,364 feet, or 1,313 feet lower than the former summit elevation.

Pyroclastic Flows

The term "pyroclastic"-derived from the Greek words pyro (fire) and klastos (broken)-describes materials formed by the fragmentation of magma and rock by explosive volcanic activity. Most volcanic ash is basically fine-grained pyroclastic material composed of tiny particles of explosively disintegrated old volcanic rock or new magma. Larger sized pyroclastic fragments are called lapilli, blocks, or bombs. Pyroclastic flows-sometimes called nuée ardentes (French for "glowing clouds") -are hot, often incandescent mixtures of volcanic fragments and gases that sweep along close to the ground. Depending on the volume of material, proportion of solids to gas, temperature, and slope gradient, the flows can travel at velocities as great as 450 miles an hour. Pyroclastic flows can be extremely destructive and deadly because of their high temperature and mobility. During the 1902 eruption of Mont Pelée (Martinique, West Indies), for example, a nueée ardente demolished the coastal city of St. Pierre, killing nearly 30,000 inhabitants.

Pyroclastic flows commonly are produced either by the fallback and downslope movement of fragments from an eruption column or by the direct frothing over at the vent of magma undergoing rapid gas loss. Volcanic froth so formed is called pumice. Pyroclastic flows originated in both ways at Mount St. Helens on May 18, but flows of mappable volume were of the latter type. The flows were entirely restricted to a small fan-shaped zone that flares northward from the summit crater.

[Graphic,21K,InlineGIF] Graphic of Mount St. Helens area showing May 18, 1980 devastation.

Pyroclastic flows were first directly observed shortly after noon, although they probably began to form a short time after the lateral blast. They continued to occur intermittently during the next 5 hours of strong eruptive activity. Eyewitness accounts indicated that the more voluminous pyroclastic flows originated by the upwelling of volcanic ejecta to heights below the rim of the crater, followed by lateral flow northward through the breach of the crater. One scientist likened this process to a "pot of oatmeal boiling over." Most of the rock in these flows was pumice. A few smaller pyroclastic flows were observed to form by gravitational collapse of parts of the high eruption column. The successive outpourings of pyroclastic material consisted mainly of new magmatic debris rather than fragments of preexisting volcanic rocks. The resulting deposits formed a fan-like pattern of overlapping sheets, tongues, and lobes. At least 17 separate pyroclastic flows occurred during the May 18 eruption, and their aggregate volume was about 0.05 cubic mile.

When temperature measurements could safely be made in the pyroclastic flows 2 weeks after they were erupted, the deposits ranged in temperature from about 570 to 785 degrees (F). As might be expected, when the hot material of the debris avalanche and the even hotter pyroclastic flows encountered bodies of water or moist ground, the water flashed explosively to steam; the resulting phreatic (steam-blast) explosions sent plumes of ash and steam as high as 1.2 miles above the ground. These "secondary" or "rootless" steam-blast eruptions formed many explosion pits on the northern margin of the pyroclastic flow deposits, at the south shore of Spirit Lake, and along the upper part of the North Fork of the Toutle River. These steam-blast explosions continued sporadically for weeks or months after the emplacement of pyroclastic flows, and at least one occurred about a year later, on May 16, 1981.

Mudflows and Floods

Volcanic debris flows-mobile mixtures of volcanic debris and water popularly called mudflows -often accompany pyroclastic eruptions, if water is available to erode and transport the loose pyroclastic deposits on the steep slopes of stratovolcanoes. Destructive mudflows and debris flows began within minutes of the onset of the May 18 eruption, as the hot pyroclastic materials in the debris avalanche, lateral blast, and ash falls melted snow and glacial ice on the upper slopes of Mount St. Helens. Such flows are also called lahars, a term borrowed from Indonesia, where volcanic eruptions have produced many such deposits.

Mudflows were observed as early as 8:50 a.m. PDT in the upper reaches of the South Fork of the Toutle River. The largest and most destructive mudflows, however, were those that developed several hours later in the North Fork of the Toutle River, when the water-saturated parts of the massive debris avalanche deposits began to slump and flow. The mudflow in the Toutle River drainage area ultimately dumped more than 65 million cubic yards of sediment along the lower Cowlitz and Columbia Rivers. The water-carrying capacity of the Cowlitz River was reduced by 85 percent, and the depth of the Columbia River navigational channel was decreased from 39 feet to less than 13 feet, disrupting river traffic and choking off ocean shipping.

Mudflows also swept down the southeast flank of the volcano-along the Swift Creek, Pine Creek, and Muddy River drainages and emptied nearly 18 million cubic yards of water, mud, and debris into the Swift Reservoir. The water level of the reservoir had been purposely kept low as a precaution to minimize the possibility that the reservoir could be overtopped by the additional water-mud-debris load to cause flooding of the valley downstream. Fortunately, the volume of the additional load was insufficient to cause overtopping even if the reservoir had been full.

[Graphic,21K,InlineGIF] Graphic of Mount St. Helens area showing May 18, 1980 devastation.

On the upper steep slopes of the volcano, the mudflows traveled as fast as 90 miles an hour; the velocity then progressively slowed to about 3 miles an hour as the flows encountered the flatter and wider parts of the Toutle River drainage. Even after traveling many tens of miles from the volcano and mixing with cold waters, the mudflows maintained temperatures in the range of about 84 to 91 degrees (F); they undoubtedly had higher temperatures closer to the eruption source. Shortly before 3 p.m., the mud- and debris-choked Toutle River crested about 21 feet above normal at a point just south of the confluence of the North and South Forks. Another stream gage at Castle Rock, about 3 miles downstream from where the Toutle joins the Cowlitz, indicated a high-water (and mud) mark also about 20 feet above normal at midnight of May 18. Locally the mudflows surged up the valley walls as much as 360 feet and over hills as high as 250 feet. From the evidence left by the "bathtub-ring" mudlines, the larger mudflows at their peak averaged from 33 to 66 feet deep. The actual deposits left behind after the passage of the mudflow crests, however, were considerably thinner, commonly less than 10 percent of their depth during peak flow. For example, the mudflow deposits along much of the Toutle River averaged less than 3 feet thick.

The Catastrophic First Minute

During the initial hours of the May 18 activity, people were obviously confused about the nature and sequence of the phenomena taking place. Did the eruption trigger the 5.1-magnitude earthquake or did the earthquake trigger the eruption? Or were both associated with some other, but unknown, cause or causes? At first, these questions and others could not be answered because of the rapidity of developments and the initial lack of firsthand observations by people who were close to the mountain and who survived the catastrophe. It was not until many hours, indeed days, later that scientists were able to reconstruct clearly the sequence of events. The reconstruction was aided by eyewitness accounts. Geologists Keith and Dorothy Stoffel, flying over the volcano in a small plane when the earthquake struck, observed "minor landsliding of rock and ice debris" into the crater. Within the next 15 seconds, the north flank of the volcano "began to ripple and churn up, without moving laterally." At the same time the Stoffels were witnessing from the air the developing debris avalanche, a remarkable series of ground-based photographs was being taken by Keith Ronnholm and Gary Rosenquist from Bear Meadows, a camping area located about 1 1 miles northeast of Mount St. Helens. Seconds after the earthquake, William Dilly, a member of the Rosenquist party, noticed through binoculars that the north flank was becoming "fuzzy, like there was dust being thrown down the side" and shouted that the "mountain was going." Within seconds Rosenquist began taking photographs in rapid succession.

Frame-by-frame analysis of the Rosenquist photographs, -- (Web Note: will not be available for this report) -- taken within a span of about 40 seconds, together with seismic and other evidence, established the following sequence of events during the first minute of the climactic eruptions. The times indicated are in hours, minutes, and seconds (Pacific Daylight Time).

The lateral blast at the vent probably lasted no more than about 30 seconds, but the northward radiating and expanding blast cloud continued for about another minute, extending to areas more than 16 miles from the volcano. Shortly after the blast shot out laterally, the vertically directed ash column rose to an altitude of about 16 miles in less than 15 minutes, and the vigorous emission of ash continued for the next 9 hours. The eruption column began to decline at about 5:30 p.m. and diminished to a very low level by early morning of May 19.

The extraordinary photographic documentation of the first minute enabled scientists to reconstruct accurately what had happened. The 5.1-magnitude earthquake caused the gravitational collapse of Mount St. Helens' north flank, which produced the debris avalanche and triggered the ensuing violent lateral and vertical eruptions. From a scientific perspective, it was fortunate that the initial May 18 events occurred during daylight hours under cloudless conditions; otherwise, the sequence of events during that crucial first minute following the earthquake would have been difficult to reconstruct precisely.

Impact and Aftermath

The May 18, 1980, eruption was the most destructive in the history of the United States. Novarupta (Katmai) Volcano, Alaska, erupted considerably more material in 1912, but owing to the isolation and sparse population of the region affected, there were no human deaths and little property damage. In contrast, Mount St. Helens' eruption in a matter of hours caused loss of lives and widespread destruction of valuable property, primarily by the debris avalanche, the lateral blast, and the mudflows.

Landscape changes caused by the May 18 eruption were readily seen on high-altitude photographs. -- (Web Note: not available) -- Such images, however, cannot reveal the impacts of the devastation on people and their works. The May 18 eruption resulted in scores of injuries and the loss of 57 lives. Within the United States before May 18, 1980, only two known casualties had been attributed to volcanic activity - a photographer was struck by falling rocks during the explosive eruption of Kilauea Volcano, Hawaii, in 1924; and an Army sergeant who disappeared during the 1944 eruption of Cleveland Volcano, Chuginadak Island, Aleutians. Autopsies indicated that most of Mount St. Helens' victims died by asphyxiation from inhaling hot volcanic ash, and some by thermal and other injuries.

MSH80_st_helens_spirit_lake_before_may_18_1980.jpg Before the devastating May 18, 1980 eruption, Mount St. Helens was considered to be one of the most beautiful and most frequently-climbed peaks in the Cascade Range. Spirit Lake was a vacation area offering hiking, camping, boating, and fishing. USFS Photograph taken before May 18, 1980, by Jim Nieland, U.S. Forest Service, Mount St. Helens National Volcanic Monument. [medium size] ... [large size] < MSH82_st_helens_spirit_lake_reflection_05-19-82.jpg Mount St. Helens and the devastated area is now within the 110,000-acre Mount St. Helens National Volcanic Monument, under jurisdiction of the United States Forest Service. Visitor centers, interpretive areas, and trails are being established as thousands of tourists, students, and scientists visit the monument daily. Mount St. Helens is once again considered to be one of the most beautiful and interesting of the Cascade volcanic peaks. USGS Photograph taken on May 19, 1982, by Lyn Topinka. [medium size] ... [large size]

The lateral blast, debris avalanche, mudflows, and flooding caused extensive damage to land and civil works. All buildings and related manmade structures in the vicinity of Spirit Lake were buried. More than 200 houses and cabins were destroyed and many more were damaged in Skamania and Cowlitz Counties, leaving many people homeless.

MSH81_damaged_home_south_fork_toutle_river_07-19-81.jpg More than 200 homes and over 185 miles (300 kilometers) of roads were destroyed by the 1980 lahars. Pictured here is a damaged home along the South Fork Toutle River. USGS Photograph taken on July 19, 1981, by Lyn Topinka. [medium size] ... [large size]

Many tens of thousands of acres of prime forest, as well as recreational sites, bridges, roads, and trails, were destroyed or heavily damaged. More than 185 miles of highways and roads and 15 miles of railways were destroyed or extensively damaged.

Trees amounting to more than 4 billion board feet of salable timber were damaged or destroyed, primarily by the lateral blast. At least 25 percent of the destroyed timber was salvaged after September 1980. Hundreds of loggers were involved in the timber-salvage operations, and, during peak summer months, more than 600 truckloads of salvaged timber were retrieved each day.

MSH80_blowdown_smith_creek_09-24-80.jpg The slopes of Smith Creek valley, east of Mount St. Helens, show trees blown down by the May 18, 1980 lateral blast. Two U.S. Geological Survey scientists (lower right) give scale. The direction of the blast, shown here from left to right, is apparent in the alignment of the downed trees. Over four billion board feet of usable timber, enough to build 150,000 homes, was damaged or destroyed. USGS Photograph taken on September 24, 1980, by Lyn Topinka. [medium size] ... [large size]

Wildlife in the Mount St. Helens area also suffered heavily. The Washington State Department of Game estimated that nearly 7,000 big game animals (deer, elk, and bear) perished in the area most affected by the eruption, as well as all birds and most small mammals. However, many small animals, chiefly burrowing rodents, frogs, salamanders, and crawfish, managed to survive because they were below ground level or water surface when the disaster struck. The Washington Department of Fisheries estimated that 12 million Chinook and Coho salmon fingerlings were killed when hatcheries were destroyed; these might have developed into about 360,000 adult salmon. Another estimated 40,000 young salmon were lost when they were forced to swim through the turbine blades of hydroelectric generators because the levels of the reservoirs along the Lewis River south of Mount St. Helens were kept low to accommodate possible mudflows and flooding.

Downwind of the volcano, in areas of thick ash accumulation, many agricultural crops, such as wheat, apples, potatoes, and alfalfa, were destroyed. Many crops survived, however, in areas blanketed by only a thin covering of ash. In fact, the apple and wheat production in 1980 was higher than normal due to greater-than-average summer precipitation. The crusting of ash also helped to retain soil moisture through the summer. Moreover, in the long term, the ash may provide beneficial chemical nutrients to the soils of eastern Washington, which themselves were formed of older glacial deposits that contain a significant ash component. Effects of the ash fall on the water quality of streams, lakes, and rivers were short lived and minor.

MSH80_may18_ash_road_connell_washington_06-80.jpg May 18, 1980 ash along the roadside, Connell, Washington. USGS Photograph taken in June 1980 by Lyn Topinka. [medium size] ... [large size]

The ash fall, however, did pose some temporary major problems for transportation operations and for sewage-disposal and water-treatment systems. Because visibility was greatly decreased during the ash fall, many highways and roads were closed to traffic, some only for a few hours, but others for weeks. Interstate 90 from Seattle to Spokane, Washington, was closed for a week. Air transportation was disrupted for a few days to 2 weeks as several airports in eastern Washington shut down due to ash accumulation and attendant poor visibility. Over a thousand commercial flights were cancelled following airport closures.

The fine-grained, gritty ash caused substantial problems for internal-combustion engines and other mechanical and electrical equipment. The ash contaminated oil systems, clogged air filters, and scratched moving surfaces. Fine ash caused short circuits in electrical transformers, which in turn caused power blackouts. The sewage-disposal systems of several municipalities that received about half an inch or more of ash, such as Moses Lake and Yakima, Washington, were plagued by ash clogging and damage to pumps, filters, and other equipment. Fortunately, as these same cities used deep wells and closed storage, their water-supply systems were only minimally affected.

The removal and disposal of ash from highways, roads, buildings, and airport runways were monumental tasks for some eastern Washington communities. State and Federal agencies estimated that over 2.4 million cubic yards of ash-equivalent to about 900,000 tons in weight-were removed from highways and airports in Washington State. Ash removal cost $2.2 million and took 10 weeks in Yakima. The need to remove ash quickly from transportation routes and civil works dictated the selection of some disposal sites. Some cities used old quarries and existing sanitary landfills; others created dumpsites wherever expedient. To minimize wind reworking of ash dumps, the surfaces of some disposal sites have been covered with topsoil and seeded with grass. About 250,000 cubic yards of ash have been stockpiled at five sites and can be retrieved easily for constructional or industrial use al some future date if economic factors are favofable.

What was the cost of the destruction and damage caused by the May 18 eruption? Accurate cost figures remain difficult to determine. Early estimates were too high and ranged from $2 to $3 billion, primarily reflecting the timber, civil works, and agricultural losses. A refined estimate of $1.1 billion was determined in a study by the International Trade Commission at the request of Congress. A supplemental appropriation of $951 million for disaster relief was voted by Congress, of which the largest share went to the Small Business Administration, U.S. Army Corps of Engineers, and the Federal Emergency Management Agency.

There were indirect and intangible costs of the eruption as well. Unemployment in the immediate region of Mount St. Helens rose tenfold in the weeks immediately following the eruption and then nearly returned to normal once timber salvaging and ash-cleanup operations were underway. Only a small percentage of residents left the region because of lost jobs owing to the eruption. Several months after May 18, a few residents reported suffering stress and emotional problems, even though they had coped successfully during the crisis. The counties in the region requested funding for mental health programs to assist such people.

Initial public reaction to the May 18 eruption nearly dealt a crippling blow to tourism, an important industry in Washington. Not only was tourism down in the Mount St. Helens-Gifford Pinchot National Forest area, but conventions, meetings, and social gatherings also were canceled or postponed at cities and resorts elsewhere in Washington and neighboring Oregon not affected by the eruption. The negative impact on tourism and conventioneering, however, proved only temporary. Mount St. Helens, perhaps because of its reawakening, has regained its appeal for tourists. The U.S. Forest Service (USFS) and State of Washington opened visitor centers and provided access for people to view firsthand the volcano's awesome devastation.

The spectacular eruption impressed upon the people in the Pacific Northwest that they share their lands with both active and potentially active volcanoes. With the passage of time, the damaged forests, streams, and fields will heal, and the memory of the 1980 eruption and its impacts will fade in future generations. The Mount St. Helens experience has been so thoroughly documented, however, that it likely will be a reminder for decades in the future of the possibility of renewed volcanic activity and destruction.

The May 18, 1980, eruption of Mount St. Helens was exceeded in "size" by many other eruptions, both in historic times and in the recent geologic past. For the study of earthquakes, two standard measures of the "size" of the seismic event are commonly used: the Richter Magnitude Scale (based on energy released as measured by seismometers) and the Modified Mercalli Intensity Scale (based on damage caused as assessed by people). Although some attempts have been made to develop a scale to compare the relative sizes of volcanic eruptions, none has yet been adopted for general use. Volcanologists have proposed and used various schemes to rank eruptions, and these generally included one or more of the following factors-height of eruption column, volume of material erupted, distance and height of hurled blocks and fragments, amount of aerosols injected into the upper atmosphere, and duration of eruption. All these factors relate directly or indirectly to the total amount of energy released during the eruption. Perhaps the two most commonly used and directly measurable factors are eruption volume and height of the eruption column.

The May 18 eruption ejected about 0.3 cubic mile of uncompacted ash, not counting an unknown but probably much smaller amount that was deposited in the, atmosphere or too diffuse to form measurable, deposits. This volume of ash is less than those of several earlier eruptions of Mount St. Helens and considerably less than the ejecta volumes of some historic eruptions elsewhere. The 1815 eruption of Tambora (Sumbawa, Indonesia) ejected about 30 to 80 times more ash than did Mount St. Helens in 1980. The 1815 Tambora eruption ranks as the largest known explosive eruption in historic times. But even the Tambora eruption pales by comparison with the gigantic pyroclastic eruptions from volcanic systems-such as Long Valley Caldera (California), Valles Caldera (New Mexico), and Yellowstone Caldera (Wyoming)- which, within about the last million years, produced ejecta volumes as much as 100 times greater.

Some scientists recently proposed the Volcanic Explosivity Index (VEI) to attempt to standardize the assignment of the relative size of an explosive eruption, using ejecta volume as well as the other criteria mentioned earlier. The VEI scale ranges from 0 to 8. A VEI of 0 denotes a nonexplosive eruption, regardless of volume of erupted products. Eruptions designated a VEI of 5 or higher are considered "very large" explosive events, which occur worldwide only on an average of about once every 2 decades. The May 1980 eruption of Mount St. Helens rated a VEI of 5, but just barely; its lateral blast was powerful, but its output of magma was rather small. The VEI has been determined for more than 5,000 eruptions in the last 10,000 years. None of these eruptions rates the maximum VEI of 8. For example, the eruption of Vesuvius Volcano in A.D. 79, which destroyed Pompeii and Herculaneum, only rates a VEI of 5. Since A.D. 1500, only 22 eruptions with VEI 5 or greater have occurred: one VEI 7 (the 1815 Tambora eruption), four of VEI 6 (including Krakatau in 1883), and seventeen of VEI 5 (counting Mount St. Helens in 1980 and El Chichon, Mexico, in 1982). Considered barely "very large," the eruption of Mount St. Helens in May 1980 was smaller than most other "very large" eruptions within the past 10,000 years and much smaller than the enormous caldera-forming eruptions-which would rate VEI's of 8-that took place earlier than 10,000 years ago.

The May 1980 eruption of Mount St. Helens has a higher VEI (5) than five of the deadliest eruptions in the history of mankind, but it resulted in the loss of far fewer lives (57). Loss of life would have been much greater if a hazard warning had not been issued and a zone of restricted access had not been established.

Since May 18, 1980, Mount St. Helens has remained intermittently active, and through early 1990 at least 21 more periods of eruptive activity had occurred. Geologists view these periods of activity as eruptive episodes of one eruption that continued through the decade, rather than separate eruptions. The first of these smaller but significant eruptive episodes began early Sunday morning, May 25, 1980, when Mount St. Helens explosively erupted ash and formed an eruption column that rose to a maximum altitude of 9 miles. At least one pyroclastic flow accompanied the vertical ash ejection. Although this eruption was considerably less energetic and voluminous than that of May 18, it nonetheless caused much concern because of memories of the events of the previous Sunday. Variable winds dispersed ash over southwestern Washington and neighboring Oregon, producing small to moderate ash falls in communities that had been spared the ash fall of May 18.

For the next 2 weeks, Mount St. Helens remained relatively quiet, puffing gas but little ash. Meanwhile, rootless steam-blast explosions continued in the northern periphery of the apron of pyroclastic flows in the valley of the North Fork of the Toutle River. On clear nights, aerial observers reported seeing glows in the vent within the crater, interpreted to reflect the near-surface presence of very ho't rock or magma, although no lava was extruded. On June 12, the volcano again erupted, generating ash falls to the south-southwest and pyroclastic flows down its north flank. The June 12 episode was similar to that on May 25 in style and volume, and both eruptive episodes were preceded by volcanic tremor a few hours in advance.

Probably within hours following the explosive activity on June 12, but hidden by poor visibility, very stiff magma began to ascend in the vent, slowly oozed onto the crater floor, and formed a bulbous lava dome (a mound of sticky lava) about 1,200 feet in diameter and 150 feet high. Such lava domes commonly form at composite volcanoes following major explosive eruptions. The formation of what was to be the first of three domes at Mount St. Helens during the 1980s was confirmed by obser vers on June 15, when visibility over the volcano improved.

Mount St. Helens erupted again in three explosive pulses during the afternoon and evening of July 22. The July eruptive episode was preceded by several days of measurable expansion of the summit area, heightened earthquake activity, and changed emission rates of sulfur dioxide and carbon dioxide. Plumes of ash rose to altitudes of between 6 and 1 1 miles. The July 22 events destroyed most of the dome formed in mid-June, and pyrociastic flows poured through the north breach of the summit crater and overrode earlier flows of May and June. No dome developed after the end of the explosive activity, which ejected only about one-tenth as much ash as did the May 25 and June 12 explosions.

During the next 3 months, explosive episodes occurred on August 7 and October 16-18. These events were preceded by differing combinations of the following precursors: increased earthquake activity, volcanic tremor, changed rates of gas emission, and expansion of the crater near the vent. Both episodes produced ash-and-gas clouds and pyroclastic flows. A small dome formed after the August explosions but was blasted away at the start of the October activity.

Another dome began to form within 30 minutes after the final explosion on October 18, and within a few days it was about 900 feet wide and 130 feet high. The October 16-18 eruptive episode turned out to be the last major explosive activity at Mount St. Helens during the 1980s. All subsequent eruptive episodes, beginning with the December 27, 1980-January 3, 1981 episode, involved predominantly nonexplosive, dome-building activity that added material to the October dome. During the remainder of 1981, five such dome-building episodes, accompanied by little or no ash ejection, took place: February 5-7, April 10-12, June 18-19, September 6-11, and October 30-November 2.

MSH80_october_dome_10-24-80.jpg A new dome started growing on October 18,1980. This October dome was 112 feet (34 meters) high and 985 feet (300 meters) wide, making it taller than a nine-story building and wider than the length of three football fields. This aerial view is from the north. This dome was not the first dome to grow in the crater. In June and August 1980, two domes formed, ony to be blasted away by the explosive events of July 22 and October 16. USGS Photograph taken on October 24, 1980, by Terry Leighley, Scandia Labs. [medium size] ... [large size] MSH81_new_lobe_spreading_center_from_west_06-26-81.jpg Betweem 1980 and 1986, Mount St. Helens' dome grew in different ways. From 1980 through 1982 the dome grew in periodic extrusions of stubby lava flows, called lobes. This pattern changed in February 1983, when growth became continuous and mostly endogenous (internal). Perioidic lobe growth, along with endogenous growth, resumed in early 1984. Pictured here is an aerial view of Mount St. Helens' dome and the June 1981 lobe with its "spreading center". A spreading center is the area from which new lava slowly emerges during lobe growth. During this time frame Mount St. Helens' lobes grew at a rate of 3 to 10 feet per hour (1-3 meters/hour) USGS Photograph taken on June 26, 1981, by Dan Dzurisin. [medium size] ... [large size]

Three eruptive episodes occurred in 1982: March 19-April 9, May 14-18, and August 18-23. A moderate explosion initiated the March-April episode, ejecting ash 9 miles high and melting snow in the crater that generated a mudflow which eventually entered the North Fork of the Toutle River. Dome growth followed this explosion. The May and August episodes reverted to the nonexplosive style and involved only dome growth. For about a month following the end of the May event, however, small explosions were frequent and at times impressive, producing spectacular vertical plumes of gas and rock debris many thousands of feet high. These were visible from Portland, Oregon (50 miles away) and, on occasion, even from Seattle (100 miles away). More than 500 similar small explosions occurred sporadically until 1986, during times when the dome was not growing. Scientists believe that these small explosions were caused by either or both of the following processes: steam blasts triggered when cold infiltrating rain and snow melt came in contact with the subsurface hot part of the dome and magma conduit, and rapid expansion of gas carried by the magma itself. Many of the explosions occurred in the late spring and early summer, when snow melt is at a maximum.

A year-long episode of eruptive activity began on February 7, 1983. It was preceded by several explosions on February 2-4 that resembled those just described. The largest of the February explosions produced plumes of gas and ash 2 to 4 miles high. The explosions ripped open a gash high on the east flank of the dome, through which lava extruded several days later. The February dome-building activity culminated in the formation of a spine-like protrusion of lava that rose about 100 feet above the summit of the dome. This spine, as did other smaller ones, lasted for only about 2 weeks and then collapsed into a heap of rubble. Slow growth of the dome took place more or less continuously throughout 1983, accompanied at times by small explosions from a crater at the crest of the dome. During this time, the dome grew not only as lava was added to its surface (extrusion) but also as magma entered and inflated the dome as if a water balloon were being filled (intrusion).

The year-long eruptive episode ended in February 1984, but activity resumed on March 29 and lasted until about April 2, producing a small lava lobe on the surface of the dome. More small explosions occurred during the spring and summer months, and on September 10-12 a large lava lobe was extruded, accompanied by major distention of the north part of the dome at unprecedented rates that approached 120 feet per day!

Considerable distention also occurred during the next eruptive episode, May 24-June 10, 1985, when the southern third of the dome was pushed more than 300 feet southward by an intrusion, leaving a deep gorge in its wake that stretched across the dome like a "smile" on a golf ball. Only a little lava oozed from the floor of this gorge (called a graben by geologists), but more than 5 million cubic yards of magma entered the dome and remained stored there.

The last two significant eruptive episodes of the 1980s occurred on May 8-13 and October 21-24, 1986. Each episode was similar, producing a large lava lobe and major internal expansion of the dome. Small explosions preceded the activity in May but not in October. These two episodes, as well as those in September 1984 and May 1985, were accompanied by much more intense earthquake activity than was associated with prior dome-building episodes. This change in style of precursory seismicity, together with the changed style of eruptive activity-from mainly extrusion to about equal occurrence of extrusion and intrusion-suggested that the magma had become stiffer and less able to rise easily to the surface than previously. Moreover, the rate of sulfur dioxide release had progressively decreased with time, suggesting that the magma was "running out of gas." Thus, scientists were not surprised that no dome growth took place during the last 3 years of the 1980's. Perhaps the series of eruptive episodes that began in 1980 has ended. However, in late 1989 periods of increased, though still weak, seismicity occurred, and in early December 1989 and early January 1990, at least three very small explosions deposited thin layers of ash in the crater. Perhaps these events either represent a "dying gasp" or are forerunners of continued or heightened eruptive activity. Time will tell.

The dome at Mount St. Helens is termed a composite dome by scientists, because it represents the net result of many eruptive events, not just one event. The dome-building process may be pictured as the periodic squeezing of an upward-pointing tube of toothpaste or caulking compound. The process is dynamic, involving the upward movement of new material, cracking and pushing aside of old material, sloughing of material from steep surfaces of the dome, and occasional, small but violent explosions that blast out pieces of the dome. These processes result in earthquakes and measurable changes in shape of the dome and nearby crater floor; study of the earthquakes and changes in shape enables prediction of the onset of eruptive episodes.

MSH81_st_helens_dome_from_deepthroat_08-22-81.jpg Mount St. Helens' lava dome in August 1981, as viewed from a photo station "Deepthroat", 1/2 mile (0.8 kilometers) away. In this view the dome is 535 feet (163 meters) high and nearly 1/4 mile (0.4 kilometers) wide, making it taller than a 44-story building (or, nearly the height of the Washington Monument) and wider than the length of four football fields. Compare with image taken August 12, 1985 from the same location with the same camera. USGS Photograph taken on August 22, 1981, by Lyn Topinka. [medium size] ... [large size] MSH85_st_helens_dome_from_deepthroat_08-12-85.jpg Mount St. Helens' lava dome as viewed from the "Deepthroat" station after five years of growth. The lava dome was 755 feet (230 meters) high and 1/2 mile (0.8 kilometers) wide in this view, making it taller than a 66-story building and almost as wide as the length of nine football fields. The dome completely fills the camera's field of view. Compare with image taken August 22, 1981 from the same location with the same camera. USGS Photograph taken on August 12, 1985, by Lyn Topinka. [medium size] ... [large size]

At the start of 1990, the composite dome was about 3,480 feet by 2,820 feet in diameter and rose about 1,150 feet above the low point on the adjacent crater floor. It has a volume of about 97 million cubic yards, less than 3 percent of the volume of the volcano (about 3.5 billion cubic yards) removed during the landslide and lateral blast on May 18, 1980. If the dome resumes growth at its average rate of the 1980s (about 17 million cubic yards per year), it would take nearly a century to fill in the summit crater and more than 200 years to rebuild Mount St. Helens to its pre-1980 size.

For a few intensively monitored volcanoes, scientists in recent years have greatly improved their capability to predict when and sometimes even where an eruption might take place, with lead times on the order of several days or less. For example, the current ability to predict eruptive episodes at Mount St. Helens represents a major advance; since 1980, all episodes (except for one very small event in 1984) have been successfully predicted several days to 3 weeks in advance. Even for accurately predicted eruptions, however, there is no way to anticipate their size or duration. Moreover, scientists are not yet able to forecast accurately the long-term future behavior of voicanoes. For example, scientists cannot answer with any certainty the following questions about Mount St. Helens: Is the intermittent activity of the 1980s over? Will another large explosive eruption comparable to that of May 18, 1980, take place within the next decade or even century? Will lava flows accompany future eruptions?

Most earth-science studies are concerned with past events, and the axiom that "the present is the key to the past" is fundamental to these studies. In recent years, as earth scientists have been asked repeatedly to look forward in time, the axiom that "the past and present are keys to the future" has become increasingly significant. Clues to the possible future behavior of Mount St. Helens are gleaned from its past eruptive history. During the past 50,000 years, Mount St. Helens has experienced nine "eruptive periods," not counting the activity of the 1980s. The term eruptive period is informally used by geoscientists for a segment of a volcano's eruptive history encompassing a series of eruptive episodes closely associated in time and/or type of eruptive processes or products; such periods are separated by dormant intervals, generally of longer duration.

The most recent and best known of the pre-1980 eruptive periods began with a major explosive eruption in 1800 A.D. For the next 57 years, this event was followed by intermittent relatively small explosive eruptions, lava flows, and the extrusion of a lava dome. Assuming that Mount St. Helens behaves as it did in the 19th century, the present activity could continue intermittently for years, possibly decades. Such activity could include the outpouring of lava flows (not observed to date), as well as renewed dome growth and small-to-moderate explosive events. The chance of another catastrophic landslide and blast comparable to that of May 18, 1980, is exceedingly low. The past history of the volcano suggests, however, that one or more explosive eruptions with heavy ash fall comparable to that of the May 18, 1980, eruption might occur before Mount St. Helens returns to a dormant state. This history of intermittent activity is one of the most important reasons why scientists continue to monitor the volcano to detect the intensive, sustained seismic activity and ground deformation that can be expected to accompany any massive infusion of new magma required to break the pattern of dome building in the 1980s and to feed an explosive eruption of major proportions.

The continuing intermittent eruptive activity at Mount St. Helens poses volcanic and hydrologic hazards for the foreseeable future, especially if eruption frequency and vigor increase. Specific hazards-ash fall, pyroclastic flows, mudflows, and floods-were described by scientists years before they became stark realities on May 18, 1980. Since then, as the volcano settled into a pattern of episodic, moderate and generally nonexplosive activity, the severity and regional impact of ash fall, lateral blasts, and pyroclastic flows have diminished. Given Mount St. Helens' alternations between explosive and nonexplosive activity in its past, however, the possibility of violent eruptions and attendant hazards in the future should not be discounted.

Considerable hazards still exist in the immediate vicinity of the volcano's present summit-the amphitheater-like crater, with its episodically active and growing composite lava dome. Whenever the composite dome enlarges, chances increase for collapses of its steep, irregular sides. Such collapses, in turn, could hurl rock fragments onto the crater floor and possibly trigger small pyrociastic flows through the crater breach and down the north flank of the mountain toward Spirit Lake. Rockfalls from the unstable steep walls of the crater have been common since the formation of the huge crater, posing a local but significant hazard to scientists working within it. Scientists and other people working close to or within the volcano's crater-within the "restricted zone" established by the USFS-must remember these hazards and take safety precautions.

Lava flows from Mount St. Helens pose little direct hazard to people or property because such flows are likely to be sluggish and, therefore, should not move fast or far from the vent. Anyone in good health should be able to outwalk or outrun the flows, and no major civil works are near enough to the volcano to be overrun by lava flows. However, such flows can melt snow and ice and thus could cause minor debris flows, mudflows, and floods.

Given the current, relatively quiet, eruptive behavior of Mount St. Helens, debris flows and floods at present constitute the greatest hazards related to volcanic activity. The potential for mudflows and floods was increased by the existence of new ponds and lakes formed when the debris avalanche of May 1980 blocked parts of the preexisting drainage to serve as natural dams. As these natural dams are composed of loose, easily erodible volcanic debris, they are structurally weak and could fail, which would trigger mudflows and floods.

MSH82_lahar_from_march_82_eruption_03-21-82.jpg Mount St. Helens erupted often between 1980 and 1986. An explosive eruption on March 19, 1982, sent pumice and ash 9 miles (14 kilometers) into the air, and resulted in a lahar (the dark deposit on the snow) flowing from the crater into the North Fork Toutle River valley. Part of the lahar entered Spirit Lake (lower left corner) but most of the flow went west down the Toutle River, eventually reaching the Cowlitz River, 50 miles (80 kilometers) downstream. USGS Photograph taken on March 21, 1982, by Tom Casadevall. [medium size] ... [large size]

Devastating mudflows or floods or both could be triggered by any or all of the following: heavy rainfall during storms, melting of snow and ice by hot eruptive products (especially pyroclastic flows), or by sudden failure of one of the lakes impounded by the debris avalanche deposits. During winter-the time of peak precipitation and maximum snowpack-the risks of mudflows and floods increase significantly. Normal precipitation in the Mount St. Helens area is heavy, especially on the volcano's upper slopes, where the average annual rainfall totals 140 inches. In a normal winter, the snowpack on the volcano's higher slopes can be about 16 feet thick. Thus, scientists and civil authorities were rightly concerned about the high potential for mudflows and floods, and the Army Corps of Engineers began to take engineering measures-including sediment-retention structures and channel dredging-in the drainages most'vulnerable to mudflow and flood hazards.

As an example of the flood hazards in the Mount St. Helens region, in August 1980 the failure of a natural debris dam caused the rapid draining of a 250-acre-feet lake in the Toutle River Valley near Elk Rock. (One "acre-foot" of water is equal to the volume contained in a one-foot layer covering one acre , or about 325 thousand gallons.) The ensuing flood damaged a partially constructed sediment- retention structure and heavy channel-maintenance equipment in the North Fork of the Toutle River. Fortunately, no injuries or deaths resulted. During the next 9 months, no large floods happened, largely because no high-intensity rainfalls occurred even though the total precipitation for the winter and spring of 1980-1981 was near normal. There were no major mudflows or floods the following winter-spring, again because rainfall generally was low intensity. Meanwhile, the levels of the lakes impounded by natural dams, however, gradually rose due to rainfall and runoff.

By the fall of 1982, the debris dams for three of the largest lakes-at Spirit Lake, Coldwater Creek, and South Fork Castle Creek-were becoming substantially filled, thereby increasing the risk of catastrophic flooding should the dams fail or be overtopped. The Corps of Engineers, which in 1981 started construction of controlled outlets at Coldwater and Castle Lakes, began also to control the rise of the level of Spirit Lake by an interim plan of barge-based pumping and discharge into outlet channels.

MSH81_coldwater_lake_outlet_channel_10-17-81.jpg Outlet channels were built at Castle Lake and Coldwater Lake (shown here) to stabilize water levels and prevent overtopping of the debris dams. USGS Photograph taken in October 17, 1981, by Lyn Topinka. [medium size] ... [large size]

The USGS and the National Weather Service installed flood-warning systems in the Toutle and Cowlitz River Valleys. By March 1983, Spirit Lake contained 360,000 acre-feet of water, the lake at Coldwater Creek had 67,000 acre-feet, and that at South Fork Castle Creek had 19,000 acre-feet. Scientists and engineers estimated that a breach of the natural dam at South Fork Castle Creek, the smallest of the three lakes, could unleash mudflows and floods comparable to those triggered by the May 18, 1980, eruption of Mount St. Helens. The Corps of Engineers and other Federal, State, and county agencies initiated a variety of projects to mitigate the growing hydrologic hazards. These mitigation projects required many people and much equipment to work in the hazardous zones close to the volcano. To ensure the safety of the mitigation operations, scientists had to intensify their monitoring efforts not only of the volcano itself, but also of the debris-clogged drainage systems.

Though less severe now than in the early 1980s, mudflow and flooding hazards should exist for many years, until such time as the slopes and areas around Mount St. Helens, by revegetation and normal erosion, return to or approach their pre-eruption forest cover, stream gradients, rates of flow, discharge, and channel dimensions. As part of a long-term plan to cope with the continuing hydrologic hazards, the Corps of Engineers, in April 1985, completed the construction of a 1.5 mile-long diversionary tunnel at Spirit Lake. This permanent tunnel system replaced the temporary, barge-based pumping operations to regulate the lake's water level.

MSH83_spirit_lake_pump_station_09-23-83.jpg From late 1982 through the spring of 1985, a pump station operated at Spirit Lake to maintain that lake at a safe level. Without pumping, Spirit Lake was estimated to overtop its debris dam within a year. USGS Photograph taken on September 23, 1983, by Lyn Topinka. [medium size] ... [large size] MSH86_spirit_lake_tunnel_10-02-86.jpg In the spring of 1985 a permanent tunnel was opened, allowing water to drain out of Spirit Lake safely. This tunnel is 11 feet (3.4 meters) in diameter and more than 1.5 miles (2.5 kilometers) in length. The water level of Spirit Lake is now maintained at approximately 100 feet (30 meters) below the estimated overtopping level. USGS Photograph taken on October 2, 1986, by Lyn Topinka. [medium size] ... [large size]

Since May 1980, the natural recovery of the drainage system around Mount St. Helens has been substantial. Yet, during this recovery period, some roads in the region sustained significant damage from mudflows and floods, and a number of homes were lost because of stream-bank erosion. How-ever, much more damage would have occurred if it were not for the construction of sediment-retention structures, dredging, and other engineering mitigation measures taken by the Army Corps of Engineers. It should be emphasized, however, the recovering drainage system has not been subjected to a truly major storm during the past decade. Thus, scientists, engineers, and government officials must continue to closely assess and monitor the continuing volcanic and hydrologic hazards. Human efforts to control the floods and sedimentation are designed not only to gain time to lessen the impact of hydrologic hazards until the natural "healing" of the drainage systems around Mount St. Helens is complete, but also to try to guide, if possible, the healing process.

The eruptive activity of Mount St. Helens has provided a good test for scientists who faced the challenge of obtaining, relaying, and explaining in easily understandable terms the information needed by the Federal, State, and local officials charged with land management and public safety. It should be reemphasized, however, that a quick response at Mount St. Helens was possible only because decades of systematic research before 1980 had contributed to a good understanding of the volcano's eruptive behavior and potential hazards. Additionally, the Mount St. Helens activity also has provided scientists a unique opportunity to learn much about the dynamics of an active composite volcano. The results of studies completed and in progress have improved the understanding of eruptive mechanisms and should refine a forecasting capability, not only for Mount St. Helens, but also for similar volcanoes in the United States and elsewhere.

When the 4.2-magnitude earthquake occurred on March 20, 1980, seismologists of the University of Washington and the USGS began a round-the-clock effort to expand the monitoring and to evaluate the seismic activity. As the number of earthquakes in- creased over the next few days, USGS and other scientists discussed with officials of the Gifford Pinchot National Forest the significance of the seismic activity, the safety of USFS facilities near the volcano, and the need to close its upper slopes because of snow avalanche and other hazards. USGS scientist Donal Mullineaux arrived on the scene the evening of March 25, and an emergency coordination center was set up at the USFS headquarters in Vancouver. The next day, Mullineaux - one of the foremost experts on Mount St. Helens - described the possible types of eruptions and associated volcanic hazards at a meeting of representatives from government and industry. Following the meeting, the USFS, State, and county officials decided to extend the area of closure beyond the immediate flanks of the volcano. The same day (March 26), the general nature of potential eruptive activity and volcanic hazards was discussed again at a joint USFS-USGS press conference. An official announcement of a Hazard Watch for Mount St. Helens was issued by the USGS at 8 a.m. PST on March.27. By 12:36 p.m. that day, the first eruption of Mount St. Helens in over a century had begun.

By the time the eruptive activity was into its second week, 25 to 30 scientists were on hand carrying out a wide variety of monitoring and volcanic-hazard-assessment studies. These scientists participated in daily meetings and briefings with USFS and other officials and provided advice on the locations of hazardous zones for use, such as the selection of sites for roadblocks to control access around the volcano. All decisions regarding access and restricted areas, however, were the sole responsibility of the USFS, State of Washington, and other land managers for the Mount St. Helens region. Ironically, in 1980 the section of land containing the summit crater was owned by the Burlington Northern Railroad; it has since been acquired by USFS by land exchanges. On March 31, an on-site, comprehensive, volcanic-hazards assessment was presented at another meeting of agencies responsible for public safety. On April 1, a large-scale volcanic-hazards map was prepared for use by these agencies. A news release was issued by the USGS on what might be expected should the activity develop into a "major eruptive phase." Scientists contributed geotechnical and volcanic-hazards information essential for preparing the "Mount St. Helens Contingency Plan" issued by the USFS on April 9. Although the possibility that the collapse of the rapidly deforming "bulge" on the north flank could trigger a magmatic eruption was considered and discussed with officials at various meetings in late April, scientists could not be sure that such an event would actually occur, let alone estimate its timing or size.

The early recognition of the potential hazards of the bulge on Mount St. Helens' north slope and the systematic measurement of its extremely rapid growth led scientists to advise the USFS that hazards were increasing. Accordingly, the USFS, State, and county officials enforced closure zones. Had these access-control measures not been taken, the catastrophic events of May 18 would have resulted in considerably more human deaths and injury. An element of luck also saved many lives. The catastrophe began hours before the scheduled departure of a caravan of landowners permitted by officials to enter the controlled access area to inspect their properties and cabins. Also, had the eruption occurred on any other day than Sunday, many more people authorized to enter the restricted areas (such as loggers, USFS personnel, and government officials) would have been at work and exposed to the danger.

Legislation passed by Congress in 1974 made the Geological Survey the lead Federal agency responsible for providing reliable and timely warnings of volcanic hazards to State and local authorities. Under this mandate, and recognizing the need to maintain systematic surveillance of Mount St. Helens' continuing activity, the USGS established a permanent regional office at Vancouver, Washington, after the May 18, 1980, eruption. On May 18, 1982, the office at Vancouver was formally designated the David A. Johnston Cascades Volcano Observatory (CVO), in memory of the Survey volcanologist killed 2 years earlier. Staffed by about 90 permanent and part-time employees-geologists, geophysicists, hydrologists, geochemists, technicians, and supporting personnel-the CVO not only maintains a close watch on Mount St. Helens, but also serves as the headquarters for monitoring other volcanoes of the Cascade Range in Washington, Oregon, and northern California. In recent years, the CVO staff has also participated in studies of eruptions or unrest at other volcanoes in the western United States and elsewhere in the world. The Cascades Volcano Observatory is a sister observatory to two other volcano observatories operated by the USGS: the Hawaiian Volcano Observatory, founded in 1912, has pioneered or refined most of the modern volcano-monitoring methods used in the world today; and the Alaska Volcano Observatory, established jointly by the USGS and the state of Alaska in 1988, studies the volcanoes of the Alaskan Peninsula and Aleutian Islands.

Throughout the 1980s, the ability of scientists at CVO and the University of Washington to provide warnings for dome-building eruptive episodes has been exceptional. Indeed, for all episodes (except for one small event) since May 1980, scientists- using data from seismic, ground deformation, and volcanic gas monitoring-have provided reliable forecasts from several hours to several days, even weeks, in advance of these events. The table gives a typical example of the timely information for one 1982 eruption given to government officials charged with emergency management and to the general public via news releases.

At Mount St. Helens, the track record for predicting eruptions, especially dome-building ones, is better than any previously accomplished for any volcano in the world. Our improving predictive ability, however, has not been tested by any large explosive eruptions.

Mount St. Helens has provided, and will continue to provide, an unprecedented opportunity for scientific research on volcanism. Relatively easy accessibility and a dense network of monitoring instruments have made Mount St. Helens a natural laboratory at which scientists can study processes typical of volcanoes elsewhere along the circum-Pacific "Ring of Fire." As Mount St. Helens is monitored continuously before, during, and after each eruptive episode, and its eruptive products are regularly sampled for chemical and other laboratory analyses, the information being compiled and interpreted yields a better understanding of Mount St. Helens in particular, and other composite volcanoes in general. Moreover, the monitoring techniques now being used at Mount St. Helens and other Cascade volcanoes are the same as, or variations of, those used to monitor the active Hawaiian volcanoes. Thus, in the rather young science of volcanology, a rare opportunity to compare the effectiveness of these techniques on two contrasting kinds of volcanoes--the Hawaiian shield volcanoes, which typically erupt nonexplosively, and the Cascade composite volcanoes, which typically erupt explosively. Scientists have learned that data from all types of monitoring are helpful regardless of the type of volcano. From such comparative studies, they will be able to determine which techniques are the most effective and reliable for monitoring each type of volcano. With such tools and broadened knowledge, scientists may be entering a new epoch in volcanology, in which significant advances in understanding volcanic phenomena will be achieved, accompanied by a sharpened ability to forecast and mitigate volcanic hazards.

Despite the troubled economy in early 1980s, tens of thousands of visitors flocked to the area surrounding Mount St. Helens to marvel at the effects of the eruption. On August 27, 1982, President Reagan signed into law a measure setting aside 110,000 acres around the volcano as the Mount St. Helens National Volcanic Monument, the nation's first such monument managed by the USFS. At dedication ceremonies on May 18, 1983, Max Peterson, head of the USFS, said,"we can take pride in having preserved the unique episode of natural history for future generations." Since then, many trails, viewpoints, information stations, campgrounds, and picnic areas have been established to accommodate the increasing number of visitors each year. Beginning in the summer of 1983, visitors have been able to drive to Windy Ridge, only 4 miles northeast of the crater. From this spectacular vantage point overlooking Spirit Lake, people see firsthand not only the awesome evidence of a volcano's destruction, but also the remarkable, gradual recovery of the land as revegetation proceeds and wildlife returns.

MSH84_st_helens_from_harrys_ridge_fireweed_august_1984.jpg Fireweed is one species of plantlife which has returned to Mount St. Helens' devastated area. Vegetation began reappearing as early as the summer of 1980 as many small trees and plants were protected by the snowpack on May 18. Seeds, carried by the wind or by animals, also entered the area and grew. By 1985, the ridges surrounding the volcano were covered with new growth. USGS Photograph taken in August 1984, by Lyn Topinka. [medium size] ... [large size]

Mountain climbing to the summit of the volcano has been allowed since 1986, and winter exploration of the crater itself is a difficult but rewarding adventure. A majestic Visitor Center was completed in December 1986 at Silver Lake, about 30 miles west of Mount St. Helens and a few miles east of Interstate Highway 5 --(Web note: Drive 5 miles east on S.R.504 from I-5 exit 49); by the end of 1989, the Center had hosted more than 1.5 million visitors. Scheduled for opening in 1992 or 1993 -- (Web note: now open: Drive 43 miles east on S.R.504 from I-5 exit 49); is an interpretation complex in the Coldwater Lake-Johnston Ridge area, from which visitors will be able to view the inside of the crater and its dome from the site of David Johnston's camp on the morning of May 18, 1980.

The National Volcanic Monument preserves some of the best examples and sites affected by volcanic events for scientific studies, education, and recreation. Intensive monitoring of the volcano is now all the more important to ensure the safety of the scientists and the monument's visitors.

[Map,18K,InlineGIF] The active and potentially active volcanoes of the principal part of the Cascade Range of the Pacific Northwest, including Mount St. Helens. The northern end of the Cascades is Meager Mountain (British Columbia), about 80 miles north-northwest of Mount Garibaldi. -- Modified from original by Lyn Topinka, 1997 [Map,31K,GIF] Sketch map showing the location of Mount St. Helens and the principal drainages and places mentione in the text. -- Modified from original by Lyn Topinka, 1997, 2002

The best way to see the effects and products of the volcano's activity is to visit the Mount St. Helens National Volcanic Monument. The next best thing is to view movies, videos, or slides about the voicano, some of which are listed here. Some school and public libraries might have them in their collections.

Mount St. Helens, A General Slide Set, produced by       
   	the U.S. Geological Survey; inquiries about availability 
   	should be addressed to the Cascades         
   	Volcano Observatory, 5400 MacArthur Boulevard,     
   	Vancouver, Washington 98661. (A set of 50         
   	slides with descriptive text, covering the eruption 
   	on May 18, 1980, and its aftermath, "before"       
   	and "after" comparisons, the growth of the lava   
   	dome, and the geologic and hydrologic studies    

Mount St. Helens, Past and Present, Beechwood
   	Films, P.O. Box 16384, Portland, Oregon 97233.
   	(While it contains no footage of the activity on
   	May 18, 1980, this 40-minute video presents an
   	interesting comparison of the areas around
   	Mount St. Helens before and after the eruption.)

Mount St. Helens, The Turmoil of Creation Continues, 
   	produced by Panorama International Productions 
   	and available from the Pacific Northwest 
   	National Parks and Forests Association, 83
   	South King Street, Seattle, Washington 98104.
   	(A 90-minute video documenting the events
   	leading to, during, and after the catastrophic
   	eruption on May 18, 1980.)

This Place in Time: The Mount St. Helens Story, a
   	Film Loft production available (by borrowing only)
   	from Film Distributi1139on Center, 13500 NE 124th
   	Street, Suite 2, Kirkland, Washington 98034,
   	(206) 820-2592. (A 22-minute, 16-mm movie 
   	highlighting the reawakening of Mount St. Helens
   	and its eruptive activity.)

Selected Readings

Brantley, Steven, and Topinka, Lyn, 1984, Volcanic studies at 
	the U.S. Geological Survey's David A. Johnston Cascades 
	Volcano Observatory, Vancouver, Washington: Earthquake 
	Information Bulletin, v. 16, no. 2, p.41-120. [A well- 
	illustrated report of the activities and workings of the 
	Observatory, which was estalblished in 1981 as sister 
	observatory to the Hawaiian Volcano Observatory (see 
	Heliker and others, 1986).]  

Crandell, D. R., and Mullineaux, D. R., 1978, Potential 
	hazards from future eruptions of Mount St. Helens, 
	Washington: U.S. Geological Survey Bulletin 1383-C, 26 p. 
	(Description of the types of eruptions and associated 
	volcanic hazards from Mount St. Helens - which proved to be 
	remarkably close to what actually took place 2 years 
	later.)  

Crandell, D. R., Mullineaux, D. R., and Rubin, Meyer, 1975, 
	Mount St. Helens Volcano: Recent and future behavior: 
	Science, v. 187, no. 4175, p. 438-441. (First publication 
	to forecast that Mount St. Helens could erupt "...before 
	the end of the century.")  

Decker, R.W., and Decker, Barbara, 1989, Volcanoes: W.H. 
	Freeman and Company, New York, 285 p. (An information- 
	packed introduction to the study of volcanoes written in 
	an easy-to-read style.)  

Editors, 1982, Volcano: in the series Planet Earth, Time-Life 
	Books, Alexandria, Virginia, 176 p. (A well illustrated 
	and readable general survey of volcanoes and their 
	activity.)  

Mullineaux, D. R., 1981, Hazards from volcanic eruptions, in 
	Hays, W. W., ed., Facing geologic and hydrologic hazards: 
	Earth-science considerations: U. S. Geological Survey 
	Professional Paper 1240-B, p. B86-B101. (A well- 
	illustrated introduction to the types, frequency, and 
	mitigation of volcanic hazards.)  

Simkin, Tom, Tilling, R.I., Taggart, J.N., Jones, W.J., and 
	Spall, Henry, compilers, 1989, This dynamic planet: World 
	Map of volcanoes, earthquakes, and plate tectonics: 
	U.S. Geological Survey, Reston, Virginia, prepared in 
	cooperation with the Smithsonian Institution, Washington, 
	D.C. (scale 1:30,000,000 at equator). (This full-color, 
	computer-generated map shows the Earth's physiographic 
	features overlain by its volcanoes, earthquake 
	epicenters, and relative movement of its major tectonic 
	plates, along the boundaries of which most of the world's 
	volcanoes and earthquakes occur.)  

Foxworthy, B. L., and Hill, Mary, 1982, Volcanic eruptions of 
	1980 at Mount St. Helens: The first 100 days: U.S. 
	Geological Survey Professional Paper 1249, 125 p. (A 
	description of the events during the first 100 days of 
	eruptive activity, in nontechnical language, that serves 
	as a back drop for the scientific articles in USGS Profes 
	sional Paper 1250.)  

Harris, S.L., 1988, Fire Mountains of the West: The Cascade 
	and Mono Lake Volcanoes: Mountain Press Publishing 
	Company, Missoula, Montana, 379 p. (This is the revised 
	and updated version of his Fire and Ice, a classic 
	summary of the volcanoes of the Cascade Range, including 
	Mount St. Helens.)  

Heliker, Christina, Griggs, J.D., Takahashi, T.J., and Wright, 
	T.L., 1986, Volcano monitoring at the U.S. Geological 
	Survey's Hawaiian Volcano Observatory: Earthquakes and 
	Volcanoes (formerly Earthquake Information Bulletin), 
	v. 18, no. 1, 72 p. (An informative and richly illustrated 
	article on the monitoring and research activities of the 
	Observatory that was founded in 1912.)  

Lipman, P. W., and Mullineaux, D. R., editors., 1981, The 1980 
	eruptions of Mount St. Helens, Washington: U.S. 
	Geological Survey Professional Paper 1250, 844 p. (The 
	most comprehensive collection of scientific articles 
	available to date, containing 62 reports on diverse 
	aspects of the 1980 eruptions.)  
	
Tilling, R. I., 1977, Monitoring active volcanoes, in U.S. 
	Geological Survey Yearbook, Fiscal Year 1977, p. 36-40. 
	(A generalized introduction to the common techniques of 
	volcano monitoring. Also available as a booklet in the 
	USGS series of general interest publications.)  

--, 1982, Volcanoes, U.S. Geological Survey series of general 
	interest publications, 46 p. (A general summary of the 
	nature, types, workings, products, and hazards of 
	volcanoes.) Tilling, R.I., Heliker, Christina, and 
	Wright, T.L., 1987, Eruptions of Hawaiian volcanoes: 
	Past, present, and future: U.S. Geological Survey series 
	of general interest publications, 54 p. (A nontechnical 
	summary, illustrated by many color photographs, of the 
	abundant data on the processes and products of 
	Hawaiian volcanoes; similar in format to this book.)  

Comments and Revisions:

• ¹ March 19, 2001, "Debris Avalanche" section revised because the velocity of the debris avalanche of 18 May 1980 was overestimated as the result of a typographical error. The incorrect speed of "155 to 180 miles an hour" has been changed to "110 to 155 miles an hour."