More energetic and frequent steam/ash explosions. Communities in which LAKAS, an organization of the indigenous Aetas, was active showed the most exemplary operation of the system:transmission was total and response was consistently appropriate. Pinatubo has been selected as one of 38 emotion-packed pictures of all time by an American online publication. Benefits of Volcano Monitoring Far Outweigh Costs–The Case of Mount Pinatubo USGS Fact Sheet 115-97. Relatively high unrest manifested by seismic swarms including increasing occurrence of low frequency earthquakes and/or harmonic tremor (some events felt). Issuance of this evacuation order for communities outside the official danger zone may have been a simple case of caution or overreaction on the part of the local officials. Very faint glow of the crater may occur but no conclusive evidence of magma ascent. 15.13 N, 120.35 E. summit elevation 1486 m. stratovolcano. The alert levels were based on instrumentally derived data and daily visual observations. SO2 emission level may show sustained increase or abrupt decrease. 2-74C (Pampanga); Report No. In order to protect against “lull before the storm” phenomena, alert levels will be maintained for the following periods AFTER activity decreases to the next lower level: From level 5 to level 4:            Wait 12 hours after level 5 activity stops, From level 4 to level 3 to 2:    Wait 2 weeks after activity drops below level 4, From level 3 to level 2:            Wait 2 weeks after activity drops below level 3. 6-km radius Danger Zone may be extended to 7 km in the sector where the crater rim is low. By June 14, 99 percent of the respondents knew of impending danger, from continued warnings and, especially, from observing the preparoxysmal eruptions (Wolfe and Hoblitt, this volume). The effectiveness of the modified transmission procedure adopted at Pinatubo was assessed by use of two indicators: (1) consistency between the warning message released by the source (PHIVOLCS) and the message received by the recipients and (2) the time gap between issuance from the source and receipt by the target public. Danger zones may be expanded to a radius of six (6) kilometers from the summit crater or active vent. Very few people were affected, because most former residents of this zone had remained in evacuation camps or resettlement areas since 1991. Frequent strong ash explosions. The fact that most respondents took appropriate defensive actions and evacuated as advised indicates that the warning system worked well enough in 1991. Probable magmatic intrusion; could eventually lead to an eruption. Generation of deadly pyroclastic flows, surges and/or lateral blasts and widespread tephra fall (ashfall). The revised alert levels allow for differentiation of large and small eruptions. The following day (June 10), Clark Air Base, a U.S. military installation near the volcano, was evacuated. Intense unrest, continuing seismic swarms, including harmonic tremor and/or “low frequency earthquakes” which are usually felt, profuse steaming along existing and perhaps new vents and fissures. Slight increase in volcanic earthquake and steam/gas activity. They had also been shown the videotape on volcanic hazards produced by the late Maurice Krafft for IAVCEI (Punongbayan and others, this volume). One is to explore the possibility of striking some correspondence between alert levels and danger zones. Low level seismic, fumarolic, other unrest. The volcano's 1992 activities were entirely different from its 1991 eruptions. On June 5, a Level 3 alert was issued for two weeks due to the possibility of a major eruption. However, there are perennial hazards (sudden explosions, rockfalls and landslides) within the four (4) kilometer-radius Permanent Danger Zone (PDZ) that may occur suddenly and without warning. In 1991, Alert Level 4 was associated with a 20-km danger zone, and Alert Level 5 was associated with both a 20-km and a 40-km danger zone. The responses to evacuation orders (a step beyond warnings) indicate that all the respondents except five (2 percent) eventually evacuated (table 7). These respondents recounted that, before the eruptions, the eruption threat and the hazards posed by the volcano had been explained to them by PHIVOLCS and other officials. 13th May 1991 – Alert Level 2. The survey covered only the survivors and is biased in favor of those who took precautions. The second evacuation was the one of the 10-20 km zone on June 7. Slight increase in seismicity. Five-level alert scheme for Mount Pinatubo, May 13, 1991. Almost all the respondents received the warning from multiple sources, with PHIVOLCS, the media, and military officials as the most common transmitters. But there were still others who refused to be evacuated (Velarde and Bartolome, 1991). In another barangay, Belbel, the barangay captain reported that some 252 tribesmen also refused to leave their homes (Anonymous, 1991b). The heightened volcanic alert level on Mt Ruapehu has been described as a "kick in the guts" for one tourism business. Low to moderate level of seismic activity. Map of the Mount Pinatubo area showing recommended evacuation zones ("danger zones") of various radii, and barangays cited in the text. Low to moderate level of seismic, other unrest with positive evidence for involvement of magma. Alcayde, Jerry, 1991, 1876 families move out of volcano area: The Philippine Star, April 22, 1991. Persistent swelling of edifice. When Alert Level 4 was declared on June 7, the danger zone's radius was increased to 20 km. Hazardous eruption in progress. Alert Level 4 will be used only for impending hazardous explosive eruptions or for ongoing eruptive activity that involves only small explosions or lava dome extrusions. [Household survey, 1991; number of respondents was 69]. A Korean pastor was finally able to convince them to leave, but they put off their departure until the next morning and spent the night in some kind of natural shelter that they called caves. Activity More Intense Eruption Probable 3. An evacuation area 20 kilometers (12.4 miles) away from the volcano was established and 25,000 people were evacuated. On the western side, most of the former residents of the sample barangays in this zone were living (officially) in the relocation sites, but many were also spending days, weeks, or even months on their preeruption land planting and gathering food, whenever they felt it safe enough to do so. Most of them did not want to leave their belongings, crops, and livestock and believed that Apo Namalyari would not let them come to harm. Therefore, evacuation was recommended only for those who had returned to the <10-km danger zone despite advice against reoccupation of the area. These were characterized by quiet effusion of lava and dome building punctuated by minor explosions and hence were not as explosive and hazardous as the 1991 events. Low to moderate level of seismicity, persistence of local but unfelt earthquakes. Because the 1992 survey was confined to the 10- to 20-km danger zone, no respondent was expected to have received an evacuation order. However, there are hazards 1 (explosions, rockfalls and landslides) that may suddenly occur within the four-kilometer radius Permanent Danger Zone (PDZ). The danger zone was shrunk back to a 20-km radius on June 18, though Alert Level 5 remained. Diliman, Quezon City Philippines 1101. Two posteruption surveys, one in 1991 and another in 1992, assessed whether eruption warnings were received, understood, and used by citizens to take protective action. These provided information on the condition of the volcano, including whether its activities would likely culminate in an eruption. [Number of respondents was 234], Table 8. St. Helens? Vigorous steaming / sustained crater glow. Multipath warning transmission has been found to create confusion, duplication, and administrative problems in some situations. Eighty-six percent of the respondents received an evacuation order, but 30 percent of these people received it 2 or more days after it was issued. Ground deformation measurements above baseline levels. Throughout the 1992 activity, PHIVOLCS merely reiterated the continued enforcement of the 10-km danger zone. Nightly News, 1991: Mount Pinatubo erupts in the Philippines The extrusion of a lava dome on June 7 led to the issuance of a Level 5 alert on June 9, indicating an eruption in progress. Magmatic, tectonic or hydrothermal disturbance; no eruption imminent. Mount Pinatubo … Gob, Fely, 1991, Rains bring death to Pinatubo evacuees: Daily Globe[Manila], April 22, 1991. The warning message consisted of hazard zonation maps, alert levels, and "danger zones," which were zones of recommended evacuation, simplified from the hazard maps. The number of casualties at the height of the June 1991 eruptions was small (only 200 to 300) despite the violence of the explosions and the vastness of the area affected. One specific aspect of the PHIVOLCS warning messages that went against UNDRO advice was the inconsistency in the danger zones associated with the various alert levels. Mount Pinatubo, Philippines, 1991. In a matter of hours on Sunday, the Philippine Institute of Volcanology and Seismology raised the alert level for Taal Volcano to Level 4 from Level 1 — with Level … Activity of Ancestral Pinatubo seems to have begun about 1.1 million years ago and probably ended tens of thousands of years or more before the birth of "modern" Pinatubo. 2 Sulfur Dioxide is a major gas component of magma. Seismic activity rises dramatically. It performed even better in 1992. Entry within PDZ must be prohibited. The final test of a warning system's effectiveness is the receipt of and appropriate response to the warning by the target recipients. The respondents were of two types: households (with the household head or an adult household member as respondent) and key informants from among barangay and municipal officials. In 1991, the failure of 18 percent of the respondents to receive preeruption warning before June 12, the failure of 14 percent of the respondents to receive an evacuation order at any time (even after the June 15 eruption), and delay in the receipt of evacuation order by 26 percent of the respondents all indicate some deficiencies in the transmission system. In order to minimize unnecessary changes in declaration of Alert Levels, the following periods shall be observed: From Level 5 to Level 4: Wait at least 24 hours after hazardous activity stops Those warnings provided enough lead time for the beleaguered inhabitants to pack up and run away from the volcano. Start studying Mt. Revised alert levels for Mount Pinatubo (revised December 1992). Some of these Aetas, members of Lubos na Alyansa ng mga Katutubong Ayta sa Sambales (LAKAS) (Negrito People's Alliance of Zambales), reported their observations to PHIVOLCS through Sister Emma, a sister of the Franciscan Missionaries of Mary (FMM) who was doing missionary work among the Aetas. Response to evacuation order, 1991. Its strengths, as well as its imperfections, provide insights on how other volcano-eruption warning systems could be developed or improved. Phivolcs chief Renato Solidum said the agency has monitored an increase in Taal volcanic activity starting March 28, 2019 but confirmed there was a … Sustained increases in SO, Intensifying unrest characterized by earthquake swarms and volcanic tremor, many perceptible. When the temporary seismic station installed near the volcano recorded high seismic activity on the first 3 days of operation, April 5-7, PHIVOLCS declared a danger zone of 10 km radius that was centered on the volcano's summit and advised evacuation of the residents from the area. Some feared lowlanders would burn their crops and homes. An evacuation area 20 kilometers (12.4 miles) away from the volcano was established and 25,000 people were evacuated. s of the active vent may be included in the danger zone. Revised alert levels for Mount Pinatubo (revised December 1992). Of those forewarned, 82 percent took protective action, including 46 percent who evacuated. Five stages of volcanic alert were defined, from level 1 (low level seismic disturbances) up to level 5 (major eruption in progress). ... raised the alert level on Mt. These maps illustrated the probable extent of the most probable hazards and served as guides for evacuation of endangered communities. In comparison, he said Taal's volcanic activity rapidly escalated starting 11 a.m. Sunday. In order to minimize unnecessary changes in declaration of Alert Levels, the following periods shall be observed: From Level 5 to Level 4:           Wait at least 24 hours after hazardous activity stops, From Level 4 to Level 3 or 2:   Wait at least 2 weeks after activity drops below Level 4, From Level 3 to Level 2:           Wait 2 weeks after activity drops below Level 3. 7 - Seismographs at Mount Pinatubo Monitoring Observatory site at Clark Air Base, Philippines. Sudden or increasing changes in temperature or bubbling activity or radon gas emission or crater lake pH. Magma is near or at the surface, and activity could lead to hazardous eruption in weeks. and Hoblitt, R.P., this volume, Overview of the eruptions. De Villa, Arturo, 1991, Aetas may go hungry: Daily Globe [Manila], June 10, 1991. In April, Aeta tribesmen who refused to move out reportedly said "they were afraid to leave their 'precious belongings&'" (Alcayde, 1991) or reasoned that they could not leave because their camote crops were due for harvesting. Evacuation orders were issued by concerned Disaster Coordinating Councils or local government officials soon after danger zones were declared on April 7, June 7, and June 14-15, 1991. The highest alert level 4 is issued, meaning that a … Luzon, Philippines. It was an andesite and dacite stratovolcano whose eruptive activity was much less explosive than modern Pinatubo.… Low level unrest. On June 13, the 20-40 km zone had to be evacuated when a level 5 alert was issued. Explosive eruption in progress. Initially, volcanologists considered employing an alert level terminology used at other Philippine volcanoes but opted to design a new one for Pinatubo (table 1). Mount Pinatubo second volcano-tectonic earthquake on August 11, 2020. Pinatubo erupted violently in June 1991, killing more than 700 people. Before June 12, the date of the first large explosive events, 82 percent of the respondents knew of the danger. Slight inflation or swelling of the edifice. Response to preeruption warning and false evacuation order. This prompted the Philippine Institute for Volcanology and Seismology (Phivolcs) to raise the alert level to 4 (out of 5) to signify an imminent hazardous … As soon as PHIVOLCS decides to issue a warning, it notifies the Office of the President and the national and local DCCs, through Volcano Bulletins and advisories that explain the condition of the volcano and recommended actions. A team from the Philippine Institute of Volcanology and Seismology (PHIVOLCS) assessed all four aspects of the Pinatubo warning system to identify areas of success and those which needed improvement. GeoNet yesterday raised the volcano alert to level … Preliminary hazard zonation maps were disseminated by PHIVOLCS on and after May 23, 1991. Intermittent steam/ash explosion and above baseline Sulfur Dioxide, Forceful and voluminous steam/ash ejections. The denser oceanic philippine plate subducted under the less dense continental Eurasian plate. The question remains, would this percentage be as large should there be a call for evacuation of areas beyond the 10-km radius? Surprisingly, 8 percent of the respondents (all from Pampanga) reported that they received an evacuation order either from municipal or barangay officials or through the media. Increasing rates of lava extrusion with increased frequency and volume of rockfall and volcanic gas flux, or abrupt decrease in volcanic gas flux due to plugging of lava at the summit crater or active vent. One of the holdouts compromised by sending his family not to an evacuation center but to a place a bit farther away from the volcano, saying "Hindi naman daw kami aabutan ng pagputok ng bundok" ("We heard that the eruption will not reach us") (Cortes, 1991). It is worth pointing out that all of the respondents contacted by the LAKAS organization showed the exemplary appropriate response. Occurrence of rockfalls in summit area. The authors are deeply indebted to Dr. Dennis Mileti and Dr. C. Dan Miller, whose comments and suggestions did not only enrich the final output but provided a rich source of learning for the authors as well, and to Dr. Chris Newhall for his patience, relentless prodding, and meticulous attention to detail. Of the 32 respondents who did not receive an evacuation order, all except two (one from the <10 km danger zone and one from the 10- to 20-km danger zone) were from the more distant, 20- to 40-km radius danger zone (table 4). On June 15th 1991, the second largest volcanic eruption of the twentieth century took place when Mt Pinatubo erupted at 1:42 pm local time. The overreaction may also be traced, at least in part, to the warning messages released by PHIVOLCS. Levels 3 and 4 of the Pinatubo scheme anticipated forecast time windows (2 weeks and 24 h) within which an eruption might occur, and each level had an interpretation of activity. Many of the people who lived on the slopes of the volcano left their villages when the eruption began in April. All monitored parameters within background levels. Ten years ago today (June 15, 2001), Mount Pinatubo in the Philippines erupted with a tremendous force, ejecting vast amounts of ash and gas high into the atmosphere; so high that the volcano’s plume penetrated into the stratosphere. Note to readers: Figures open in separate windows. Criteria. However, those who died constituted a very small percentage of the population at risk, so the resulting bias is deemed insignificant. Danger zones may be expanded to a radius of ten (10) kilometers or more from the summit crater or active vent. Phreatic explosion or ash puffs may occur. In practice, the latter distinction was largely lost.] The alert level-danger zone association, though not intentionally established, lingered, so that when Alert Levels 4 and 5 were released in 1992, an understandable reaction was to react as in 1991 and evacuate the 10- to -20-km danger zone. Elevated levels of any of the following: volcanic earthquake, steam/gas emission, ground deformation and hot spring temperature. Respondents who received preeruption warning and (or) false evacuation order. Critics of the multipath transmission procedure claimed that had PHIVOLCS stuck to the DCC channel instead of directly dealing with the media, reporters would not have been able to cite it as their source for their false or sensationalized reports. Small earthquakes swarm (20-180) per day occurred beneath Mt. Notable increase in the temperature of hot springs.
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