REPORT:
Volcanic Event Notification at Mount St. Helens

Hundreds of small gas and ash emissions also occurred during 1980-86, most without recognizable precursors. The lack of precursors made advance warning of these events impossible; instead, information statements were issued after the larger, more visible events. The occurrence of occasional small, unpredictable, ash-producing explosions at Mount St. Helens during 1989-91, coupled with increased concern about the hazards of volcanic ash to aviation, prompted CVO to develop a seismic-alarm system that triggers on small volcanic events. This alarm system activates CVO's 24-hour telephone beeper. In addition, the Federal Aviation Administration (FAA) can also activate the CVO beeper to report possible volcanic activity. These two modifications improve CVO's response time for non-predictable, sudden-onset events and help the FAA quickly verify pilot reports of possible volcanic plumes.

Figure 1:

Since 1980, this notification system has been modified in response to changes in volcanic activity, funding, and the concerns of government, business, and the public. Key changes include the capability of issuing written predictions weeks in advance of most eruptions; eliminating the need for 24-hour duty for both USFS/ECC and CVO staff except when eruptions are imminent; entering all predictions and updates into a computer "news" system for easy review by those on the call-down list; updating volcanic activity reports when the volcano is quiet; and, most recently, developing a seismic alarm to alert scientists to small events that occur without precursors.

For most eruptions, a series of statements was issued (table 1), usually beginning with an "extended outlook advisory" predicting an eruption within several weeks. As the levels of precursory activity increased, the predicted eruption window was fine-tuned to days or hours, and "eruption advisories" and "eruption alerts" were issued. After an eruption began, factual statements were issued regarding the character and effects of the eruption, and, finally, a statement was issued declaring the eruption to be over. The "daily updates" and information tapes for the public and media provided additional information on a daily basis (table 2).

If the ECC and CVO, in Vancouver, and the UW seismic laboratory, in Seattle, were not already staffed on a 24-hour basis when an "eruption advisory" was issued, 24-hour duty was initiated. USFS, CVO, and UW personnel were ready to respond to rapid changes in the level of volcanic activity and to answer questions and discuss specific concerns. Because it was not always possible to determine whether there would be explosive activity during and eruption, there were regular discussions among the Federal Aviation Administration (FAA), National Oceanographic and Atmospheric Administration (NOAA), National Weather Service (NWS), USFS/ECC, and CVO personnel regarding the possibility of ash plumes and their probable trajectories. CVO and the USFS reported suspected ash-producing events to the FAA as quickly as possible, and the FAA called the ECC or CVO to confirm all pilot reports. Initially the FAA was contacted at the local Portland, Oregon area office; however, by the mid-1980's most contact with the FAA was made directly with the regional FAA office in Auburn, Washington (Hamley and Parkinson, 1994).

Most of these events took place without recognized precursors, which made advanced warning of these events impossible. Verbal or written statements were issued to all concerned agencies after the larger or more visible events (table 3). If an event occurred during normal working hours, the ECC and CVO updated media and public information telephone tapes and contacted the FAA, emergency management officials, and others on the call-down list shortly after the event. Because the seismic amplitude of these events was too small to trigger alarms on the UW State-wide network, scientists were often unaware (until normal working hours) of events that occurred during non-working hours. In most cases, this was not a problem because these small events were frequent enough that government officials and the public became familiar with them. However, the FAA and emergency management personnel occasionally needed to contact CVO for more information after the larger events that may have been visible to pilots or the public. This contact was made by calling the USFS/ECC telephone beeper number; the USFS, in turn, contacted the CVO duty scientist by telephone or through the beeper, if necessary.

During 1989-91, at least six, small, ash-producing explosions occurred at Mount St. Helens, ending a 3-year period during which no eruptive activity took place. Because none of the 1989-91 explosions had recognizable precursors, they were not predicted, and no advance warnings were issued. The first of these ash-producing explosions (December 7, 1989) occurred during normal working hours; however, the second explosion (January 6, 1990) occurred on a rainy Saturday morning, and scientists were unaware of the event until several hours later when residents of central Washington began reporting light dustings of ash on their cars. In fact, CVO was not immediately notified when ash began falling. Instead, calls from the public prompted the media to contact the Alaska Volcano Observatory (AVO) to see if the ash was from ongoing activity at Redoubt Volcano, near Anchorage. AVO verified that the ash was not from Redoubt and contacted CVO geologists.

Seismic Alarm System

An RSAM-based seismic-alarm system was developed and installed for testing 2 days after the January 6, 1990, event and was fully functional by the end of February 1990. With the RSAM system, a computer program compares the amplitude of a station's average seismic signal during a 1-minute interval with empirically determined threshold values. If thresholds are exceeded during the same 1-minute interval at several (usually three) of the stations in the crater and on the volcano flanks, an RSAM alert is generated. The computer is set to automatically dial the duty scientist's 24-hour beeper and transmit a number code indicating an RSAM alert. The computer redials the beeper every time a new 1-minute RSAM alert is generated.

Many types of events, including explosions, rockfalls, earthquakes, and telemetry problems, can generate alerts (table 4). Because an alert does not indicate the nature of the event, the duty scientist must examine the seismic signature of the event recorded on the seismographs at CVO to determine the basis for the alert. Explosion signals can usually be identified by careful evaluation of the signal character (Jonientz-Trisler and others, 1994). Once an alert is received, the speed with which notification is issued will depend on the time it takes for the duty scientist to reach CVO and the scientist's skill at recognizing explosion signals (table 5).

To date, all known ash-producing explosions since March 1, 1990, have generated alerts. However, failure of any component (key seismic stations, computer, computer programs, phone system, beeper, or beeper-pager system) would prevent an alert from getting through. As a precaution, a daily test alert is sent through the system to the beeper.

Better Two-Way Communication

Dissemination of information through normal USFS channels may also be delayed if CVO should need to contact the USFS by beeper. To assure that the FAA and NOAA are immediately notified of any ash-producing event, they are contacted directly by CVO as soon as the signal is identified. If the USFS is delayed in responding to their beeper, CVO will initiate further call-down by notifying the Washington Department of Emergency Management and others as needed.

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