Summit caldera and pit craters on Mauna Loa, Hawaii. The inset shows Mauna Loa as it appears from the Hawaiian Volcano Observatory, 240 kilometers away.

Mauna Loa Volcano erupted in July 1975, following a quarter century of inactivity. The first hint of change leading up to the 1975 eruption was a marked increase in the number of earthquakes beginning in April 1974, more than a year before the eruption. Inflation or swelling of the summit of Mauna Loa was detected 4 months later during the annual "laser beam" remeasurement of horizontal distances across the summit crater. The 1974 set of measurements showed the first significant increases in the horizontal distances of the lines across the summit crater since the beginning of the precise distance monitoring program in 1967. The Hawaiian Volcano Observatory immediately alerted Hawaiian officials and the general public to the possible reawakening of Mauna Loa from its long slumber.

During the next 12 months, both the ground deformation and seismic networks on Mauna Loa were expanded. Records showed that the numbers of earthquakes and the rate of summit inflation increased steadily, reaching a climax during the summit eruption that began on July 5, 1975. The exact timing of the eruption could not be predicted, even though all premonitory indicators pointed toward an eruption any day. Although the earthquake frequency tapered off sharply in the weeks following the July eruption, swelling of the summit resumed, indicating that magma was continuing to accumulate in Mauna Loa's summit reservoir. Measurements made on six separate occasions over a period of a year and a half following the eruption all confirmed continued swelling. From analysis of the written records of the past historic eruptive behavior and the fact that both the earthquakes and swelling had extended out along the northeast rift, Observatory scientists suggested that a flank eruption on the northeast rift was likely sometime before the summer of 1978, .if Mauna Loa were to behave as it had for the past 200 years. This conclusion was conveyed to members of the Hawaiian Congressional delegation and Hawaii Civil Defense officials, announced to the media, and published in a scientific journal.

In fact, Mauna Loa did not erupt again until March 1984. The eruption began at the summit and spread to the northeast rift zone in a few hours. The resulting lava flows advanced to within 6 kilometers of Hilo before the 3-week-long eruption ended in early April.

These recent developments show that a few years of intensive monitoring and the short historic record (about 200 years) are simply inadequate to establish statistically reliable probabilities for the exact time and place of the next eruption.

Kilauea has been closely monitored for a longer period of time than Mauna Loa, but the necessary state of knowledge for prediction of eruptive activity has not been achieved. There have been some notable successes, however. For example, in the late 1960's and early 1970's, several eruptions were predicted with sufficient certainty 4 to 8 hours in advance, so that HVO scientists could advise officials of Hawaii Volcanoes National Park to evacuate certain sections. The park rangers were able to clear park visitors safely from the actual outbreak areas in ample time. But there also have been false alarms-- when all of the premonitory indicators signaled movement of magma from the summit reservoir, only to have the magma injected into the rift zones below ground without breaking through to the surface.

The latest eruption at Kilauea began in January 1983 along the east rift zone. Spectacular lava fountains in the first 3 years of the eruption produced lava flows that moved rapidly down the volcano's south flank and destroyed homes in the Royal Gardens subdivision. In 1986, the site of the eruption changed to a different vent. This phase of the eruption has produced much less magma, but even so many homes in the coastal town of Kalapana have been destroyed.

Mount St. Helens about noon on May 18, 1980, some 3 hours after the beginning of the catastrophic eruption that devastated the area north of the volcano and showered ash over much of eastern Washington.

In March 1980, Mount St. Helens, one of the explosive volcanoes of the Cascade Range in the Pacific Northwest, roared back to life after being dormant for 123 years. Mount St. Helens' activity climaxed with the catastrophic eruption of May 18, 1980, which caused the worst volcanic disaster in the recorded history of the United States. Mount St. Helens continues to be intermittently but weakly active--most recently in 1991--and may remain active for years or even decades. In 1981, the Geological Survey established the David A. Johnston Cascades Volcano Observatory (CVO) in memory of the USGS volcanologist killed during the May 1980 eruption. This facility is a sister facility to the Hawaiian Volcano Observatory and serves as the headquarters for the continued monitoring of Mount St. Helens as well as for monitoring studies of other potentially active Cascade volcanoes.

The Geological Survey has published several fully illustrated volumes on the 1980 eruptions of Mount St. Helens:

Lipman, P.W., and Mullineaux, D. R., 1981, editors, 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.)

Foxworthy, B.L., and Hill, Mary, 1982, Volcano 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 the eruptive activity in nontechnical language that serves as a backdrop for the more technical articles in Professional Paper 1250.)

Tilling, R.l., 1987, Eruptions of Mount St. Helens: Past, Present, and Future: Reston, Va., U.S. Geological Survey general interest publication, 46 p. (A nontechnical overview of the geology and history of the past and present eruptive activity at Mt. St. Helens and speculations about its future behavior.)

HVO scientists making magnetic and geoelectric measurements over an active lava tube on Kilauea's East Rift Zone with the source vent Pu'u O'o in the background. (Photograph by J.D. Griggs, USGS.)

In May 1980 the Mammoth Lakes resort area in California, on the eastern slope of the Sierra Nevada mountain range, was racked by a historically unprecedented series of earthquakes. Since then, accelerated seismic and ground deformation monitoring studies have shown measurable uplift of the ground--as much as 50 centimeters locally. The Mammoth Lakes area lies in the southwestern part of the Long Valley Caldera, a large volcanic crater formed by collapse during violent eruptions about 700,000 years ago. Scientists are interpreting the persistent, but periodic, unrest to be related to subsurface movement of magma known to lie a few miles below the caldera. Intensive monitoring of the region is continuing to detect the earliest precursors of possible renewed volcanic activity.

Leveling survey on Kilauea's east rift zone with Pu'u O;o in the background. (Photograph by J.D. Griggs, USGS.)

A small eruption occurred in November 1985 at the summit of Nevado del Ruiz, a glacier-capped volcano in the Andes in Colombia, South America. The hot volcanic ejecta melted snow and ice, and the meltwater then mixed with loose volcanic debris to trigger devastating mudflows that swept down several valleys and killed more than 25,000 people, causing the second worst volcanic disaster in the world in this century. In contrast to the El Chichon disaster in 1982, the Ruiz eruption did not come as a surprise. Scientists had known for a year earlier that the volcano was showing signs of possible eruptive activity. Unfortunately, despite recommendations made by volcanologists, no definitive volcano-monitoring studies were mounted until only several months before the eruption. While useful, the few monitoring data were inadequate to provide the detailed information required for proper contingency planning. Nonetheless, post-disaster analyses clearly have documented that the 1985 Ruiz disaster could have been averted had the civil authorities acted more effectively. A nagging question, however, remains unanswered: Might the authorities have taken more decisive action if they had been provided longer term and diagnostic monitoring data? We will never know. The tragic lesson from the Ruiz case study is that, for volcano-monitoring data to be most useful, they must be gathered and analyzed for a long time--the longer the better--before a volcanic crisis develops.

Geologist programs an automated video time-lapse system on the north flank of Redoubt Volcano in Alaska.

In March 1988, under a cooperative program between the USGS and the state of Alaska, the Alaska Volcano Observatory (AVO) was formed. The facility significantly extends the USGS' capability for monitoring the active volcanoes of the Alaska Peninsula and the Aleutian Islands. The scientists of AVO, together with colleagues from its sister observatories (HVO and CVO), have been busy monitoring the eruption of volcanoes located along the Cook Inlet southwest of Anchorage, Alaska, including Redoubt Volcano and Mount Spurr. Seismic monitoring provided the first warning signals of the 1989 eruption of Redoubt Volcano, and the AVO's current monitoring includes monitoring of ground deformation as well as volcanic gas emissions.



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