REPORT:
Preventing Volcanic Catastrophe:
The U.S. International Volcano Disaster Assistance Program

Introduction

Unfortunately, a storm on November 13, 1985, obscured the glacier-clad summit of Nevado del Ruiz. On that night an explosive eruption tore through the summit and spewed approximately 20 million cubic meters of hot ash and rocks across the snow-covered glacier. These materials were transported across the snow pack by avalanches of hot volcanic debris (pyroclastic flows) and fast-moving, hot, turbulent clouds of gas and ash (pyroclastic surges). The hot pyroclastic flows and surges caused rapid melting of the snow and ice, and created large volumes of water that swept down canyons leading away from the summit. As these floods of water descended the volcano, they picked up loose debris and soil from the canyon floors and walls, growing both in volume and density, to form hot lahars. In the river valleys farther down the volcano's flanks, the lahars were as much as 40 meters thick and traveled at velocities as fast as 50 km/h. Two and a half hours after the start of the eruption one of the lahars reached Armero, 74 kilometers from the explosion crater. In a few short minutes most of the town was swept away or buried in a torrent of mud and boulders, and three quarters of the townspeople perished (Figure 1).

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Figure 1 -- Armero, Colombia, destroyed by lahar on November 13, 1985.More than 23,000 people were killed in Armero when lahars (volcanic debris flows) swept down from the erupting Nevado del Ruiz volcano. When the volcano became restless in 1984, no team of volcanologists existed that could rush to the scene of such an emergency. However, less than a year later, the U.S. Geological Survey organized a team and a portable volcano observatory that could be quickly dispatched to an awakening volcano anywhere in the world. -- USGS Photo by R.J. Janda.

After the fatal eruption, volcanologists of the U.S. Geological Survey were dispatched to Colombia, to quickly establish a seismic and tiltmeter network at the volcano to help Colombian scientists assess the likelihood of future eruptions and lahars. At the same time, a painstaking search began for the circumstances that led to the disaster.

It soon became clear that no single factor was responsible for the disaster. Contributing factors were a lack of a timely hazards evaluation (a hazard map took nearly a year to complete after the first signs of volcanic unrest and was available for distribution only days before the eruption), an inadequate monitoring system at the volcano, and ineffective procedures for communicating information and making decisions during the emergency. In hindsight, the disaster at Nevado del Ruiz could have been prevented.

The realization that disasters like that at Nevado del Ruiz might be prevented launched the Volcano Disaster Assistance Program (VDAP) in August 1986. With support from USAID through its Office of Foreign Disaster Assistance, the U.S. Geological Survey created VDAP to assist developing countries during volcanic crises. During its short existence, VDAP has assisted Ecuador, Colombia, Guatemala, the Philippines, and other countries to reduce the loss of life and property from volcanic eruptions and to prepare for future volcanic crises. The successful response to the 1991 eruption of Mount Pinatubo in the Philippines stands as VDAP's most extraordinary contribution to volcano-hazard mitigation (see Earthquakes and Volcanoes, v. 23, no. 1, 1992). (Figure 2)

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Figure 2 -- Aerial view of Mount Pinatubo after the cataclysmic June 15, 1991. A joint team from the US Geological Survey and the Philippine Institute of Volcanology and Seismology (PHIVOLCS) worked closely to assess hazards and monitor and predict eruptive activity at Mount Pinatubo in 1991. The accurate characterization of the hazards and timely warnings of eruptions led to the evacuation of approximately 56,000 people--including 14,500 U.S. servicemen and their dependents--from high-hazard areas near Mount Pinatubo days before the volcano's climactic eruption. -- USGS Photo by E.W. Wolfe

Goal and Strategy of VDAP

• Develop the capability to rapidly deploy a volcano-monitoring network anywhere in the world.
• Assist local scientists in geologic studies to assess volcano hazards.
• Work with local scientists to interpret monitoring data and to disseminate hazard information.
• Train local scientists to use monitoring techniques to forecast volcanic eruptions.

The ability to respond rapidly with volcano-monitoring equipment is not sufficient by itself to mitigate volcano hazards. Although an early scientific response to a reawakening volcano is critical to making reliable forecasts of the timing and nature of future eruptions, hazard mitigation is most effective when volcanoes have been monitored for many years before eruptive activity begins. To assist local scientists, VDAP provides the monitoring equipment and personnel needed to quickly establish an effective volcano-monitoring network. Data gathered by the network helps volcanologists to forecast eruptive activity and issue timely eruption warnings. (Figure 3)

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Figure 3 -- Response to the Mount Pinatubo crisis in the Philippines. USGS and PHIVOLCS personnel install a seismic station near Mount Pinatubo six weeks before the devastating eruptions. Installation of a monitoring network is a team effort. -- USGS Photo by J.A. Power.

The record of a volcano's past eruptive activity is preserved in the volcanic rocks and unconsolidated volcanic deposits that surround the volcano. Evaluation of a volcano's past eruptions by dating these deposits and determining their mode of origin, provides information about the nature of possible future eruptive activity and associated hazards at the site. The results of these studies, summarized in volcano-hazard assessments and hazard-zonation maps, help public officials to prepare land-use maps and determine risk during emergencies.

The program has the best chance of success when VDAP and host-country scientists have worked together for a period of time before volcanic unrest becomes a crisis. Thus, VDAP scientists are cooperating with scientists from other countries to help them prepare for future volcanic activity in their countries (Figure 4). Workshops and training programs for participants from developing countries are conducted in the US and in the host countries. To meet the needs of the many Spanish-speaking host countries, USGS publications about volcano hazards and volcano monitoring are translated and published in Spanish as well as English.

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Figure 4 -- International cooperation in volcano monitoring. VDAP fosters cooperative efforts in volcano monitoring and volcano-hazards mitigation in several countries in Central and South America. Personnel from Ecuador's Geophysical Institute of the National Politechnical University and VDAP staff discuss modifications to standard USGS seismic components. -- USGS Photo by J.W. Ewert.

What is VDAP

The fields of expertise of the core team include geology, geophysics, hydrology, and electronics. The team plans daily operations, purchases and develops equipment, and participates in all VDAP responses. Other scientists, from within and outside the USGS, supplement the core group as needs arise. The second component is a complete cache of monitoring equipment that functions as a portable volcano observatory. Much of the equipment was developed or modified by the USGS with the essential characteristics that it must be durable, relatively inexpensive, and easily transported. The monitoring equipment can be set up quickly and is self-contained.

In addition, the VDAP staff continually strives to improve hardware and software systems to enhance the monitoring capabilities of volcano observatories.

Benefits of VDAP

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Figure 5 -- Telemetry tower 8 kilometers north of Mount St. Helens, Washington. This tower, part of the network that monitors activity at Mount St. Helens, transmits data directly to the Cascades Volcano Observatory. Work at Mount St. Helens in the 1980s resulted in advances in monitoring technology and understanding of volcano behavior that were then applied at other volcanoes in the United States and abroad. -- USGS Photo by S.R. Brantley.

Another consequence of VDAP is the extent to which volcano-monitoring systems are standardized and widely distributed in both developed and developing countries. Use of standardized equipment makes it possible for Central and South American countries to cooperate in installing, maintaining, or exchanging components of the system and in interpreting data in familiar formats.

VDAP'S PORTABLE VOLCANO OBSERVATORY

Figure 6 -- (not online) Volcano-monitoring flow chart. This diagram shows the flow of data in VDAP's portable volcano observatory. Data recorded at sensors in the field (top) are transmitted to the observatory (bottom), where all data are entered into a PC-based computer system for display and analysis. The acronyms are defined in the text.

Monitoring techniques have vastly improved due to the recent advances in electronics and the development of the personal computer (PCs). A portable volcano observatory is now possible because of the large storage capacity and rapid data analysis that can be accomplished with a PC. The use of PC's makes it possible for scientists to quickly establish a complete monitoring network at a restless volcano with a nearby data-storage and data- analysis base station. This has proven extremely important for geologists conducting field work at restless volcanoes, both for their personal safety and for correlating field observations in real time with geophysical data so as to effectively update hazard assessments during rapidly changing conditions.

Technological advances and wider experience in monitoring volcanoes in the United States and abroad since the eruption of Mount St. Helens in 1980 have helped scientists to give better advance warning of eruptions and to detect volcanic events underway, especially explosive eruptions and lahars. As the tragedy at Nevado del Ruiz demonstrated, people at risk need to know about explosive eruptions and lahars as soon as possible. Each eruption that has been monitored by the USGS in the past 14 years has led to improved understanding of volcanic systems and has made possible more accurate interpretations of subsequent monitoring data. For example, scientists have recognized certain common patterns and styles of seismic activity that occur before eruptions. These patterns of pre-eruptive activity have been useful in forecasting the onset of eruptions. Some seismic signals (called long-period earthquakes) appear to be related to magmatic-gas pressure and in the future may serve as a basis for forecasting the relative size of explosive eruptions. Described below are key components of the portable observatory developed by the USGS in the last 10 years, plus new data-collection and data-analysis systems and new instrumentation designed to detect explosive eruptions and lahars. We discuss the key components of the data gathering, storage, and analysis system, and we highlight a few techniques and instrumentation that are part of VDAP's volcano-monitoring "tool box."

Seismic System

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Figure 7 -- Seismograph in action at Pinatubo response. Signals from some seismometers are always recorded on analog drum recorders. Despite advances in computer-based data acquisition, drum recorders are still needed. A glance at the seismogram wrapped around the drum gives experienced volcanologists a quick appreciation of the current level of seismic activity at the volcano. -- USGS Photo by R.P. Hoblitt.

Once earthquake epicenters and hypocenters are determined either interactively or automatically, several different programs can be used to view the earthquake data graphically. One of the programs displays a one-page summary of earthquake activity that can be included in a "daily update" of a volcano's activity. The summary combines an earthquake epicenter plot and a hypocenter cross section (Figure 8). An interactive program plots earthquake locations both on a map and a cross section in chronological sequence. The program can rotate a group of hypocenters about any axis, draw cross sections along any azimuth through the volcano, and print a hardcopy of the display. This capability is very useful because it allows scientists to visualize the hypocenters in three dimensions and to identify spatial patterns that might indicate faults or magma conduits. The ability to visualize the seismic activity in three dimensions also makes it easier for scientists to convey to public officials the current status of a volcano's activity.

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Figure 8 -- Earthquake summary plot (Mount Pinatubo, May 7 to June 8, 1991. Epicenters are plotted on the map at the left; hypocenters are shown on the east-west cross section on the right (the epicenter of an earthquake is a point on the surface directly above the focus or hypocenter of the earthquake).

Real-time Seismic Analysis

The RSAM computes and stores the average amplitude of ground shaking caused by earthquakes and volcanic tremor over 10-minute intervals. Increases in tremor amplitude or the rate of occurrence and size of earthquakes cause the RSAM values to increase. Rather than focusing on individual events, RSAM sums up the signals from all events during 10- minute intervals to provide a simplified but still very useful measure of the overall level of seismic activity (Figure 9). This information is easy to plot and convey to public officials.

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Figure 9 -- Real-Time Seismic-Amplitude Measurement (RSAM) plot. Comparison of RSAM data (top) and seismograms (bottom) shows how RSAM reduces complex seismic data to a simple line graph that correlates with ground-shaking energy. Eruptions (heavy dark lines) from Mt. Redoubt occurred at 09:47 am, and 10:15 am on the 14th and 15th of December, 1989.

The Seismic Spectral-Amplitude Measurement (SSAM) system takes this approach one step further by computing in real time the average amplitude of the seismic signals in specific frequency bands (Figure 10). This permits seismologists to evaluate the nature of seismicity at a volcano and recognize subtle shifts in frequency that are related to changing dynamics of magma movement.

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Figure 10 --Seismic Spectral-Amplitude Measurement (SSAM) plot (Mount Pinatubo, the Philippines, June 15, 1991). This plot shows the average relative seismic amplitude in specific frequency bands over 15 minute intervals. This type of seismic data is available in real time, and permits seismologists to detect and evaluate a change in the type of earthquake activity occurring beneath an active, restless volcano. In the figure, the time scale refers to Greenwich mean time (G.m.t.). Brief episodes of intense seismicity in the 0.5-1.5 Hz frequency band between approximately 0200 and 0530 were associated with explosive eruptions. Intense tremor during the first part of the climactic eruption began at about 0540 and gave way after approximately 3 hours, as the eruption waned, to higher-frequency seismicity related to structural readjustments of the volcano. Data gaps result from loss of power to the system during the evacuation of Clark Air Base.

Deformation Monitoring

VDAP's equipment cache includes EDMs, theodolites, and reflectors needed to survey key points (benchmarks) on a volcano for detection of surface deformation. This traditional surveying method requires a clear line of sight between the benchmarks on the volcano and the instrument site at its base, which is often difficult to achieve. Increasingly, GPS receivers are being used to measure horizontal deformation because this technique does not require a clear line of sight between benchmarks (Figure 11). Compared to conventional surveying, the ease with which deformation data can be collected with GPS makes this a very attractive method.

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Figure 11 -- Global Positioning System (GPS) receiver at Cotopaxi Volcano, Ecuador. GPS uses data transmitted by orbiting satellites to locate points on the ground. The USGS has made baseline GPS measurements at several volcanoes in the United States and in Latin America. In the event of an awakening of one of these volcanoes, GPS receivers would be set up at these points again to determine whether or not measurable deformation had occurred and to monitor for precursory deformation that might herald an eruption. -- USGS Photo by J.W. Ewert.

A typical GPS survey deploys several receivers at benchmarks on the volcano to collect satellite data simultaneously at several points. The data are then downloaded and processed on a PC. This strategy works well in non-hazardous situations to gather baseline location data for comparing to future measurements. However, a GPS campaign requires someone to repeatedly deploy and retrieve the receivers. Such repeated entry into a zone of high hazard on a volcano that is threatening to erupt may represent an unacceptable risk. For this reason scientists at CVO designed a telemetered GPS monitoring system, using unattended stations, that is being tested on Augustine Volcano in Alaska. As we continue to develop the system, we expect it to become part of the portable volcano observatory.

Low-Data-Rate Telemetry

Gas Emission

Data Analysis

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Figure 12 -- Composite plot showing various types of data monitored at Mount St. Helens, Washington (October 15-24, 1986). The data base and analysis program called BOB was used to prepare this plot. Experience gained with the eruptions of Mount St. Helens and other volcanoes shows that the most accurate predictions of volcanic activity can be made when several different parameters are monitored. Arrows indicate when a dome-building eruption began. Using the program BOB, all types of monitoring data can be compared on a common time base.

Analysts have ready access to a wide variety of data made available by the user- friendly BOB program. Additional programs are written in BASIC computer language to work with the BOB software and enable modifications and enhancements to be made easily by staff members with minimal programming experience. With these programs, observatory staff can print plots showing all or part of the data for the last few minutes, days, or months with a single command. By providing the means to manipulate and scan time-series data from multiple sources and various time periods, BOB significantly enhances the usefulness of the VDAP monitoring system.

Detection of Explosive Eruptions

VDAP uses lightning detectors and microbarographs to help confirm the onset of explosive eruptions. Lightning is commonly associated with ash-producing eruptions and can occur either in the eruption column or in the eruption cloud that drifts away from the volcano. Lightning discharges produce broad-band radio waves that can be detected at a considerable distance. VDAP uses a simple lighting-detection system that was originally designed to warn golfers of approaching thunderstorms. It cannot determine signal strength or azimuth to the source of the lightning; it can only detect the presence of lightning in the vicinity.

Explosive volcanic eruptions can also produce small, sharp fluctuations in atmospheric pressure that can be easily measured with a microbarograph. VDAP's microbarograph system consists of a sensitive pressure transducer, installed either at the local observatory or near the volcano. The resulting signals are recorded continuously on a drum recorder, where they can quickly be compared to the current level of seismic activity.

Detection of Lahars

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Figure 13 -- Acoustic Flow Monitor (AFM) site in the Drift River valley, near Redoubt Volcano, Alaska. The key component of the AFM system is a seismometer, buried in the ground nearby, that responds to the high-frequency (10-300 Hz) vibrations that characterize lahars. Inspired by the Nevado del Ruiz tragedy in 1985, the AFM system was developed and tested at Mount Redoubt, and then successfully used in the Philippines to monitor lahars at Mount Pinatubo. -- USGS Photo by S.R. Brantley.

The system consists of a network of acoustic flow sensors deployed at increasing distances from a volcano along rivers that head at the volcano. The flow sensors are geophones (seismometers) sensitive to high-frequency ground vibrations. The peak amplitudes in three different frequency bands (10-300 Hz, 10-100 Hz, and 100-300 Hz) are sampled every second. If the peak amplitudes exceed set thresholds for a set time, an alert is transmitted to the observatory. Lahars can be distinguished from other events on the basis of their high-frequency character even during eruptions and earthquakes (Figure 14).

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Figure 14 -- An Acoustic Flow Monitor (AFM) plot (above). Example of AFM data from a lahar at Redoubt Volcano. An explosive eruption generated the lahar that was detected by acoustic flow sensors located progressively farther from the volcano. Map (below) shows station locations.

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The acoustic flow monitor has several features that give it versatility and durability. Most importantly, unlike a systems employing trip wires, the acoustic flow monitor system uses a non-contact method of flow detection to avoid repetitive and hazardous maintenance of equipment after each flow. Like all VDAP field systems, the acoustic flow monitor is weatherproof, rugged, and has proven effective at remote sites under extreme temperature and humidity conditions. A unique feature of the system is a two-way radio link that allows users to obtain data and query the acoustic flow monitor on site to obtain current data or modify system operating parameters.

SUMMARY

List of Acronyms

CVO       Cascades Volcano Observatory
EDM       Electronic Distance Meter
GPS       Global Positioning System
OFDA      Office of Foreign Disaster Assistance
PC        Personal Computer
PHIVOLCS  Philippine Institute of Volcanology and Seismology
RSAM      Real-time Seismic-Amplitude Measurement
SSAM      Seismic Spectral-Amplitude Measurement
USAID     United States Agency for International Development
USGS      United States Geological Survey
VDAP      Volcano Disaster Assistance Program