In managing vulnerability to natural disasters, with case studies of volcanic disasters on non-industrialized islands

Figure 11-1: Mount Pinatubo’s Location Within The Philippines


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Figure 11-1: Mount Pinatubo’s Location Within The Philippines

(modified from, accessed on May 10, 1998)


Air Base

Subic Bay Naval


The Philippines has 48 land volcanoes and 5 sea volcanoes which have erupted in the past 10,000 years (Smithsonian Institute, 1997). Except for exceptionally brief mentions of the Mount Pinatubo eruption in 1991, neither Brands (1992) nor Steinberg (1994) mention volcanoes, indicating that volcanology is not a particularly important political priority or historical influence for the Philippines. Table 11-1 lists some examples of volcanism in the Philippines. The devastation from the 1951 eruption of Hibok-Hibok volcano was exacerbated by the complete lack of preparation in the Philippines for a volcanic eruption and was the impetus towards creating the Commission on Volcanology (COMVOL), the forerunner of PHIVOLCS, which was founded in 1952 to prevent a similar situation from occurring (Tayag and Punongbayan, 1994). PHIVOLCS has ensured that the Philippines is reasonably prepared for responding to volcanic events, but they have been strengthened by a close, lengthy relationship with the USGS which arose from the historical links between the two countries and continues due to contemporary bonds.

Table 11-1: Selected Volcanic Eruptions in The Philippines





Mayon, Luzon

Many dead.

October 23-27, 1766

Mayon, Luzon

more than 2,000 dead

February 1, 1814

Mayon, Luzon

more than 2,200 dead


Mayon, Luzon

1,500 dead

1835, 1886, 1888

Mayon, Luzon

no information

June 23-30, 1897

Mayon, Luzon

more than 400 dead

January 27-30, 1911

Taal, Luzon

1,335 dead and 199 severely injured


Hibok-Hibok, Camiguin

500 dead


Taal, Luzon

200 dead

September 1984

Mayon, Luzon

no deaths, 73,000 evacuated

June 10-15, 1991

Mount Pinatubo, Luzon

500-1000 dead, at least 200,000 evacuated (see text in this chapter)

February 2, 1993

Mayon, Luzon

70 dead, 60,000 evacuated

11.2 Mount Pinatubo

Mount Pinatubo (see Figures 11-1 and 11-2) is located at 15.13N and 120.35E, 100 km northwest of Manila, with a current summit elevation of 1,600 m above sea level. Before 1991, Mount Pinatubo was classified as a dormant volcano. Widespread damage occurred during its last eruption in 1380, well before permanent settlement of the area (Davis, 1992) and thus outside the temporal scope of Filipino and indigenous societies. Although the area was known for its geothermal energy potential, there had been minimal volcanic activity between the late 14th century and 1991. Mount Pinatubo had been studied superficially, but there was no indication that it might be a concern. Because it was not perceived that Mount Pinatubo would ever pose a threat, neither planning nor preparation were completed for an eruption there.

Figure 11-2: Region Around Mount Pinatubo with Volcanic Hazard Zones

(from, accessed on May 10, 1998)

The temporal sequence of events of the eruption of Mount Pinatubo which started in 1991 is well-documented (e.g., Ewert and Newhall, 1992; PVOT, 1991; WGBH, 1992; Wolfe, 1992) and summarized in Table 11-2. Although these references were “factual” accounts of events, there were often discrepancies amongst them. Table 11-2 attempts to collate the information in the references and provides the most popular dates and data for the listed events. If a table entry seems ambiguous, it emulates the references.

Table 11-2: Chronology of the 1991 Eruption of Mount Pinatubo

(summarized from Ewert and Newhall, 1992; PVOT, 1991; WGBH, 1992; Wolfe, 1992)

Date in 1991


April 2

Multitudinous, small steam and mud explosions from Mount Pinatubo end the volcano’s 611-year dormancy. 5,000 residents within 10 km of the summit are soon evacuated.

April 22

USGS scientists travel to the Philippines in response to requests from PHIVOLCS and concerns about possible damage to Clark. The USGS-PHIVOLCS team becomes PVOT.

June 3

A small explosion leads to almost continuous, increasing seismic and volcanic unrest.

June 7-9

The evacuation zone is raised to within 15 km and then 20 km of the summit. 20,000 residents are evacuated. Most aircraft at Clark are evacuated.

June 10

14,500 Americans and all remaining aircraft, except for three helicopters, are evacuated from Clark. 1,500 personnel remain. PVOT moves to the side of Clark farthest from Mount Pinatubo, about 25 km from the summit (Clark is approximately 8 km wide).

June 12

The first large explosion from Mount Pinatubo creates an enormous ash cloud. The evacuation zone is raised to within 30 km of the summit and more than 33,000 Filipinos are evacuated along with 600 Americans from Clark. Eruptions continue throughout the night.

June 13

A large explosion occurs in the morning.

June 14

At 1309h, the climactic eruptive phase begins.

June 15

The climactic eruption of Mount Pinatubo starts at 0555h followed by almost continuous eruptions throughout the day. Typhoon Yunya makes landfall at 1400h as a tropical storm and passes 50 km north of Mount Pinatubo. All remaining personnel leave Clark at 1430h. Most of PVOT’s remote monitoring equipment on and around Mount Pinatubo has ceased functioning.

June 16

At least 200,000 people are displaced from the Mount Pinatubo area.

Basic military personnel and PVOT return to Clark and new instruments are set up on the volcano by June 18th.

To the present

Lahars and small eruptions continue to devastate the surrounding area, destroying crops and houses and killing livestock and people.

Estimates of deaths from the eruption range from “approximately 200” (Davis, 1992, p. 303) to “nearly 500” (Kerr, 1991, p. 514) and exact numbers quoted include 320 (PVOT, 1991, p. 545) and 435 (Krafft, 1993, p. 194). Most of the victims were crushed when the volcanic ash and tephra layers covering roofs absorbed water from Typhoon Yunya (which had been downgraded to a tropical storm early on June 15th)18 and the extra weight collapsed the roofs. One American soldier died when his vehicle skidded on rain-slicked and ash-covered roads. Many deaths were thus a result of the combination of two simultaneous natural disasters rather than a consequence of either the volcano or the typhoon (Ewert and Newhall, 1992; PVOT, 1991; Wolfe, 1992).

The most devastating effects of Mount Pinatubo occurred far beyond June 1991, though there are no consistent compilations of casualties. These effects involved lahars and the evacuated population. The threat from lahars (see also section 11.3.4) will continue for several more years--at least 100,000 people were left homeless by lahars from Mount Pinatubo in 1995 (“Like Pompeii”, 1996)--and has exacerbated the deleterious effects of temporary camps set up for evacuees from the eruption. By late October 1991, more than 100,000 Filipinos still resided in temporary camps and plans to permanently resettle them were just commencing (PVOT, 1991). There were also several instances of lahar warnings and evacuation orders being ignored by Filipinos who had spent time in these camps and who preferred to risk the lahars rather than return to camps where there were continuing casualties from disease, malnutrition, and exposure (Tayag and Punongbayan, 1994). The Aetas suffered similarly (section 11.3.2).

PHIVOLCS states (Tayag and Punongbayan, 1994) that “The management of the Pinatubo Volcano eruption crisis of 1991-92 represents the highest point in the development of volcanic disaster mitigation in the Philippines” (p. 2). Despite their feeling of readiness, PHIVOLCS continues (Tayag and Punongbayan, 1994) that “The hazards unleased by Pinatubo, however, have certain characteristics for which the country has been poorly equipped by its four decades of volcanic disaster mitigation experience” (p. 2), but that they are learning from the problems they had in order to be better prepared next time. As well, many Filipinos panned the government’s response to the crisis (“Volcano preparations lacking...”, 1991) and the lack of long-term planning for evacuees could and should have been ameliorated long before Mount Pinatubo’s activities began. Considering that 2 million people were highly vulnerable to Mount Pinatubo, there were comparatively few casualties and PHIVOLCS and other participants should be commended for their efforts and successes; however, irrespective of the apparent success, there were numerous problems during Mount Pinatubo’s eruptions. Many of these problems relate to the role of technology and the role of the engineer, as discussed in section 11.3.

11.3 Role of Technology

11.3.1 American Influence

Clark Air Base and Subic Bay Naval Station contributed US$1 billion per year and 68,000 direct jobs to the economy of the Mount Pinatubo region (Steinberg, 1994) but were a continuing source of damage to the Philippines’ pride as a reminder of dependency on colonial powers (Brands, 1992; Steinberg, 1994). The presence of the military bases contributed to the American interest in the eruption and the military provided housing, communications, helicopter support, and some money to PVOT which assisted enormously in monitoring and predicting the volcano’s behaviour. Without the involvement of the American military, many of these resources--including accommodations at Clark, which was a relatively secure location with electricity in close proximity to the volcano--would have been unavailable and the PVOT’s activities would have been much more challenging.

The Mount Pinatubo eruption wrecked most of Clark and severely damaged Subic Bay in the midst of difficult negotiations to extend the Americans’ lease on the bases beyond September 16, 1991. The Americans decided to abandon Clark but to negotiate for Subic Bay. A deal was reached between the Americans and Filipinos which was rejected by the Filipino Senate. The Americans then announced that they would leave Subic Bay. The specific reasons are difficult to discern--for example, Brands (1992) and Steinberg (1994) assign widely disparate levels of importance to Subic Bay during the 1991 Gulf War to eject Iraqi troops from Kuwait--but the failure of the August 1991 communist coup in Moscow and the apparently impending break-up of the Soviet Union was as important as uncertainty about Mount Pinatubo’s future activity. In any case, Mount Pinatubo was one of many factors which contributed to the final outcome.

Irrespective of the American interest in the military bases, USGS’ mandate was clearly to assist the Filipino government (through PHIVOLCS) as part of VDAP, rather than to focus on the threat to the military bases. Since its inception in 1986, which was in direct response to the tragedy at Nevado del Ruiz, Colombia in 1985 (see section 5.3.3), VDAP has assisted eleven countries on four continents in responding to volcanic hazards. The 1991 Mount Pinatubo eruption was VDAP’s “most extraordinary contribution to volcano-hazard mitigation” (USGS, 1997a). Given the extensive interest of the Americans in maintaining a military presence in the Philippines (Brands, 1992; Steinberg, 1994), it would seem that the military bases provided an overriding impetus for USGS to become heavily involved in investigating Mount Pinatubo without being the sole cause.

As part of VDAP, USGS brought with them new software and hardware which were applied to monitoring, modelling, and predicting Mount Pinatubo’s behaviour, and which made the tasks much easier and more accurate. PHIVOLCS relied on USGS to create, bring, apply, operate, maintain, and interpret results from the needed technology (Bowler and Joyce, 1991; Kerr, 1991; WGBH, 1992). USGS and VDAP incorporate the fundamental goals of training others to use imported technology and promoting self-sufficiency (USGS, 1997a) but these goals were not always achieved.

The main constraining factor was the temporal scale of the natural hazard (section 6.3). There appear to have been ardent intentions to train PHIVOLCS in using USGS’ technology, but the first priority had to be appropriate decision-making and advice for evacuations. The volcano could have erupted on any day following the initial activity, and even if the exact timeframe for eruptions had been predicted with confidence in advance, only the short time period between April 22 and the beginning of June (see Table 11-2) could have been used for training--amongst all the other required tasks. The long-standing relationship between USGS and PHIVOLCS mentioned in section 11.1 also provided an ideal atmosphere for technology transfer, but the temporal scale of Mount Pinatubo’s activities did not always permit such principles to be put into practice.

The best practical situation under the circumstances was for USGS, who knew their technology well, to control operations, with PHIVOLCS learning as much as possible through observation and imitation. This point refers to the involvement of the American military too, discussed earlier, since the Filipinos had neither the expertise nor the resources to supply the necessary logistical support. The American influence on technology used during the Mount Pinatubo events might seem colonial and domineering (which it was) but the alternative was to avoid the use of such technology, likely resulting in tens of thousands of deaths.

11.3.2 Aetas

(This section collates and analyzes material from England (1993a and 1993b), Goertzen (1991), and Shimizu (1989)).

The Aetas were devastated by the eruption and relief efforts seemed unprepared for, and uninterested in, responding to their cultural needs and values. Mount Pinatubo was a divine protector to the Aetas and the volcano’s activity was an enormous psychological blow to them, indicating that they (or perhaps non-Aeta loggers and miners) had terribly angered the volcano. The complete destruction of their land and villages added despondency because the Aetas are proud of their self-reliance and believe that the slopes of Mount Pinatubo are the only place for them to live. Government plans to build new settlements and to permanently relocate them were initiated without the Aetas’ consent and were eventually thwarted by the lack of cooperation from the Aetas.

Instead, the Aetas were left in temporary camps where they were forced into the horrendous indignity (to them) of accepting charitable support of food and clothing. As well, more than 600 Aeta children died of malnutrition and diseases such as measles in the camps in 1991 (PVOT, 1991), which is significantly more than the death toll during the actual eruption. The Aetas refused some of the food aid and much of the proffered medical services due to unfamiliarity; Western-style medicine and food are unnatural for them whereas death is normal and acceptable. The relief efforts neither anticipated nor responded to these cultural values. Two years after the eruption, the Aetas became tired of waiting in camps and commenced the return to their homes on the volcano’s slopes against the instructions of the Filipino authorities. The Aetas prefer being self-reliant and in danger rather than being safe but dependent, yet this factor was never considered by others.

There is not much which an engineer could have done to alleviate the situation. Without a long history of engineers and other professionals cooperating with the Aetas to demonstrate that Western food and medicine are acceptable and to assist them in designing safer communities with more bountiful crops, the Aetas will be mistrustful about outside help. They have a society with a low level of technology but a strong feeling of the need for self-reliance, so irrespective of how sensitive an engineer is to the Aeta culture or how much the technology is moulded for the Aetas’ needs, the Aetas will refuse the assistance due to mistrustfulness and pride. This situation exemplifies the impact on technology’s success and vulnerability to natural hazards of ingrained cultural/philosophical boundaries (sections 3.3 and 6.4.1).

11.3.3 Land-Use Planning

An extremely successful pre-disaster action for minimizing casualties from a volcanic eruption is to forbid the populace from settling in areas which are deemed to be highly vulnerable. Prohibiting human habitation within 10 km of Mount Pinatubo was only proposed three years after the eruption, by Tayag and Punongbayan (1994), when lahars (section 11.3.4) were causing damage. Enforcing such a directive, however, is challenging. The Aetas (section 11.3.2) refuse to live away from Mount Pinatubo’s slopes. Meanwhile, rural Filipinos trying to eke out a subsistence living would oppose orders to avoid good land because of potential volcanic threats, particularly when they do not understand, and do not care to understand, the full implications of a volcanic eruption (PVOT, 1991). Present hunger and pride are no match for potential, future dangers.

Preventing encroachment into volcanic areas is an effective long-term preventive solution which is often inappropriate, untenable, and unjust. Nonetheless, more investigation into and discussion of this issue would have been helpful as part of PHIVOLCS’ mandate since its inception. For example, enlisting the cooperation of engineers for community design could assist in creating communities with reduced vulnerability to volcanic hazards--even on the slopes of a volcano. Warning systems and emergency response plans could be developed along with structures which are designed to be less vulnerable to volcanic hazards. Structures identified as important--such as schools, hospitals, and emergency services--could be designed with a higher level of safety than other structures. Hydrological engineering and surveying would also permit the least vulnerable locations for communities to be identified and would indicate how engineering works might be integrated into the environment to reduce vulnerability and environmental impact. Such concepts are not new or innovative; in fact, they have been applied to earthquake, tornado, and hurricane engineering, and to less dramatic natural hazards, for years. Applying similar engineering techniques to volcano engineering--coupled with education about hazards and individual and community response measures--would reach a compromise where land-use around a volcano was neither forbidden nor highly vulnerable.

11.3.4 Design Loads

The main damage to engineered structures from Mount Pinatubo came from ash and tephra falls and lahars. Section 11.2 described how the majority of deaths during the eruption occurred as a result of the combination of Mount Pinatubo’s ash and tephra falls and Typhoon Yunya. Volcanic material accumulated on roofs and readily absorbed water from the typhoon’s rain. The weight of wet ash and tephra collapsed the roofs and crushed victims. This situation epitomizes the concerns espoused about how past experience influences vulnerability (section 3.3) and creates challenges for engineering design (section 4.4.2) along with the design challenge presented by conjunctive events (section 4.4.3).

Designing roofs for this case would have entailed anticipating a conjunctive event which had never before been experienced in the Philippines and which is not mentioned in the literature of other volcanic eruptions or potential volcanic hazards. Furthermore, anticipating the conjunctive events of one the worst volcanic eruptions in the twentieth century along with a severe (category 3 out of 5) typhoon would have been stretching the boundaries of plausibility. Even if such a prediction had been accepted, the cost of designing for such a load could well have been beyond the means of rural Filipino communities. This situation illustrates the economic influences on vulnerability discussed in section 3.4.

In this situation, the engineer would be responsible for ensuring that the limits of the design load were known and understood at the time of construction. Then, in the few days leading up to June 15, 1991 when it became apparent that Typhoon Yunya might strike Mount Pinatubo, the engineer should have been able to work with volcanologists to anticipate the threat of water-soaked ash and tephra and to communicate the hazard and appropriate safety measures to the population. Unfortunately, there appeared to be no engineers on PVOT nor on the local emergency committees. Additionally, as seen in Table 11-2, Mount Pinatubo’s activity was intense from approximately June 10th--before Typhoon Yunya’s formation (see footnote 1 in section 11.2). The lack of engineers present during the crisis could have been rectified, and should be altered for future events. The complete dominance of the volcanic threat during Typhoon Yunya could not have been altered, since it is nature’s contribution. While engineers and additional resources might have provided the opportunity for identifying the wet ash and tephra hazard, there would have been no guarantee of success. In any case, an important lesson in volcanic hazards has been learned for future instances.

In contrast to the difficulty of anticipating the wet ash and tephra hazard, lahars are a well-known volcanic hazard (section 9.2.4), and received international publicity and much academic interest after the disaster at Nevado del Ruiz, Colombia in 1985 (details are in section 5.3.3). Lahars have occurred each year following the 1991 eruption of Mount Pinatubo, with material being remobilized during the rainy season by typhoons as well as by regular showers (information in the remainder of this section is from “Like Pompeii” (1996), Tayag and Punongbayan (1994), and Tiglao (1996)). Estimates of casualties vary widely, but lahars have buried several towns, clogged rivers in the area, devastated hundreds of square kilometers of land in layers several meters thick, killed a few hundred people, and displaced tens of thousands of people, with some locations undergoing several evacuations over the years.

Despite the knowledge of and continuing threat from lahars, the response to Mount Pinatubo lahars has been abysmal. Theory and planning for engineering countermeasures have been exhaustively explored (see Table 11-3) but translation to practical results has failed miserably. For example, concrete dams are recommended for intermediate and long-term measures, yet no attempt has been made to construct any. Instead, dikes made from lahar material are used because of the low cost and the abundance of lahar material. By 1994, 9 of 22 check dams had collapsed and they had all been filled by lahars--although inundation of downstream communities was prevented temporarily. In 1996, a US$40 million lahar dike was breached for 67 m. Repair work and further construction have been delayed by disagreements, corruption and incompetence.

The Public Works Department complains that PHIVOLCS, particularly the director Dr. Raymundo S. Punongbayan, failed to predict lahar behaviour. Dr. Punongbayan not only denies the charges but also has publications (e.g., Tayag and Punongbayan, 1994) which clearly spell out the threat long before the catastrophic lahars of 1996--although whether Dr. Punongbayan communicated this information to the Department is not clear. Dr. Punongbayan retaliates to the accusations by complaining of poor design and construction of the dikes by the Department. The Public Works Department also takes issue with criticisms from American-Filipino geologist Kelvin Rodolfo, a professor at the University of Illinois. Rodolfo offers criticisms of, and proposes improvements to, the Department’s dike plans, but the Department downplays the identified problems and blames both nature’s power and the lack of funds.

The lack of funds, however, stems from mismanagement. In 1995, less than one quarter of expected lahar infrastructure funds were released, of which less than half were actually used. In 1996, President Fidel Ramos pledged plenty of money for dike projects but did not appropriate any in the national budget. As well, dike and catchment basin projects have rarely been built according to plan, are

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