Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Journal of Research and Didactics in Geography (J-READING), 0, 1, Dec., 2012, pp. 25-33 DOI: 10.4458/1005-04 The reduction of volcanic risk in the Neapolitan area Roberto Scandonea, Lisetta Giacomellia a Dipartimento di Matematica e Fisica, Università di “Roma Tre”, Rome, Italy Email: [email protected] Received: October 2012 – Accepted: November 2012 Abstract The Neapolitan area may be affected by the activity of the two volcanoes of Vesuvius and Campi Flegrei. Contingency plans have been formulated for Vesuvius and should be implemented in case of observations of anomalous precursory signals. The high population density makes the success of any large scale evacuation plans unlikely. We revise the effect of past historical eruptions which occurred in the area, and suggest possible alternative measures that can be taken by individuals also during the course of an eruption. Keywords: Volcanic Risk, Vesuvius, Campi Flegrei, Eruption 1. Introduction Volcanic Risk has been defined (Fournier, 1979) as the product R = Value x Vulnerability x Hazard where the Value is the total amount of lives or properties at risk of a volcanic eruption, the Vulnerability is the percent of value at risk for a given volcanic event, and the Hazard is the probability that a given area be interested by a certain volcanic phenomenology. The reduction of volcanic risk can be obtained by diminishing the number of inhabitants and the properties at risk of a volcanic eruption. The first objective can be achieved by evacuation plans that should be implemented before the imminence of an eruption. The second objective is more difficult as it requires a long term planning of the urban Copyright© Nuova Cultura development of a volcanic area. The general experience in Italy, as well as in other parts of the world, has shown that an increasing number of people, as well as industrial and urban development are occupying larger areas exposed to different natural hazards (Wharton Risk Management and Decision Processes Center, 2008). This general tendency is difficult to be countered as it is driven by strong economic interests. Furthermore, large numbers of people living in endangered areas make it difficult to work out large scale evacuation plans as has been seen during the Katrina event in New Orleans (Cigler, 2009). The Neapolitan area is characterized by a very high population density (Pesaresi et al., 2008), and may be affected by the activity of the active volcanoes of Vesuvius, (Figure 1) and Italian Association of Geography Teachers 26 Roberto Scandone, Lisetta Giacomelli Campi Flegrei (Figure 2) (Scandone et al., 1993). Studies on the volcanic hazard of the area started 40 years ago (Scandone, 1977), but have been unable to prevent an irregular and massive urbanization of the area. The large growth of population after the 50s has resulted in more than 850,000 people now living in the close proximities of the two active, but quiescent volcanoes. Figure 1. Transverse aerial view of the summit cone of Mt Vesuvius. In the background the settlements on the flanks of the volcano and the city of Naples. Photo: Roberto Scandone, Lisetta Giacomelli. Figure 2. Transverse aerial view of the western area of Napoli (Agnano) within Campi Flegrei. The craters of Solfatara , (on the right) and Nisida (in the background) were formed in pre-historical time. Photo: Roberto Scandone, Lisetta Giacomelli. Copyright© Nuova Cultura Italian Association of Geography Teachers Roberto Scandone, Lisetta Giacomelli In case of volcanic unrest, emergency plans, available only for Vesuvius, enforce the evacuation of about 500,000 inhabitants from the communities surrounding the volcano. Given the unknown pattern of possible precursors, and the high number of people that would be affected by such measures, it is likely that the pre-planned contingency measures may not work. There is a similar situation also in the area of Campi Flegrei with more than 350,000 people residing in zones that may be affected by volcanic phenomena. In this paper we examine several historical volcanic eruptions in the area and identify some critical issues that may jeopardize the measures taken to reduce the impact of volcanic phenomena. 2. Historical explosive eruptions in the Neapolitan area and their impact on human environment The first problem to understand during a volcanic crisis is the character of the eruption, as an effusive event with the emission of lava flows will affect only the buildings and agricultural land, but not human life. On the contrary, an explosive eruption destroys everything around the volcano up to a distance, depending on the violence, of 10-25 km. Neapolitan volcanoes have mixed styles of activity: Campi Flegrei displays a predominant explosive activity, whereas Vesuvius has had a predominant effusive style in the last 300 years, but predominant explosive activity after long quiescence periods, like those which preceded the violent eruptions of 79 A.D., and 1631, or the present one. In the following we will examine the three explosive eruptions that occurred at Vesuvius and Campi Flegrei after long quiescence periods. 3. The eruption of Vesuvius of 79 A.D. Vesuvius is a volcano well known for its devastating eruption during Roman time in 79 A.D., which destroyed the cities of Pompeii and Herculaneum killing thousands inhabitants (Giacomelli et al., 2003). Pliny the Younger Copyright© Nuova Cultura 27 described the eruption, and the attempted rescue of the inhabitants made by his uncle Pliny the Elder, the admiral of the Roman fleet. The description closely fits the reconstruction of the eruption based on the interpretation of volcanic deposits (Sigurdsson et al., 1985). The eruption was preceded by earthquakes that lasted for many days, with several crises occurring also decades before (Cubellis et al., 2007). The early phase started at midday of 24 August of 79 A.D., and was characterized by a sustained eruption plume formed by the eruption of a mixture of fragmented magma and gas rising to a height of 24 to 32 kilometers above the crater. The prevailing stratospheric wind caused the dispersion of the plume toward SE and the deposition of a thick layer of pumice with a thickness of up to 3 meters in Pompeii. It is likely that, during this phase, the area to the east of the volcano was in a total darkness. Herculaneum, to the SW, was relatively less affected in the early phase. During the night between the 25 and 26, the violence of the eruption increased and there was the emplacement of several pyroclastic flows caused by the collapse of the eruption plume and the sliding along the flank of the volcano of a dense mixture of hot gas, ashes and pumice which determined the complete destruction of all buildings, and living creatures within a radius of 10-15 kilometers from the volcano (Figure 3). A total of about 5 km3 of magma were erupted in less than 48 hours (Sigurdsson et al., 1985). In Pompeii, 394 corpses were found in the pumice fall deposits and 650 in the pyroclastic flows (Figure 4). About 90% of the first group were found in houses, and were probably killed by the collapse of roofs because of the pumice weight; a smaller number of victims were found outside of buildings, probably killed by falling roof slates or by larger rocks thrown out by the volcano. An equal number of corpses, in the pyroclastic flows, were found inside and outside the houses (Giacomelli et al., 2003). A total of about 1,500 victims was estimated taking into account also the unburied part of the town. The total number of people living in Pompeii was between 10,000 and 20,000 which gives a percent ranging between 15 and 7.5% of people who remained in town and were killed by the eruption. Italian Association of Geography Teachers 28 Roberto Scandone, Lisetta Giacomelli Figure 3. The ruins of Pompeii lie at a distance of 8 kilometers from Vesuvius. Photo: Roberto Scandone, Lisetta Giacomelli. Such percentages are surprisingly low for people who did not know that the mountain above their city was an active volcano or did not know anything about volcanoes. We do not know whether those that escaped were killed or not by the eruption, but however they reacted to the events and attempted an escape to their fate. A similar percentage of victims versus total number of inhabitants is found in Herculaneum 4. The eruption of Monte Nuovo in Campi Flegrei in 1538 The eruption started on 29 September 1538 after more than two years of occasional earthquakes and ground deformation. On the day before the eruption, the seismic activity dramatically increased along with the rapid uplift of the ground, which rapidly dried the beach near the Copyright© Nuova Cultura Figure 4. Cast of one of the victims of the eruption of 79 A.D. of Vesuvius. Photo: Roberto Scandone, Lisetta Giacomelli. site of the eruption (Parascandola, 1947). The eruption began with explosions driven by the interaction between the magma and sea-water, Italian Association of Geography Teachers Roberto Scandone, Lisetta Giacomelli and progressed to a typical Strombolian eruption with mild explosion ejecting scoria and rapidly building a small cone because of the accumulation of scoria and cinder, and forming a new hill (Monte Nuovo). The eruption lasted several days and caused destruction in the immediate surrounding of the eruption site destroying the village of Tripergola along with a hospital and ten thermal baths. The seismic activity caused widespread damage in the nearby city of Pozzuoli that was almost all leveled to the ground (Parascandola, 1947). A group of about 15 people, who had climbed the cone during a period of relative calm on 10 October, was killed by a sudden explosion. Most of the people living in Tripergola and Pozzuoli escaped from the villages in the night before the eruption, because of the strong 29 seismic activity which terrorized everyone. A testimony reported: “In the year 1538, in the day of St Jerome (28 September) a big earthquake was felt in the city, which was shaking up and down, and all the city revolted and was all evacuated, and everyone was going to Naples or in the fields and it seemed as the all world was falling down. People were running naked, and while I was running with my wife and children, I saw, in the proximity of the city doors of Pozzuoli, a lady named Zizula, wife of master Geronimo Barbiero, who, vested of only one shirt and wildly uncombed, was riding a horse like a man, and everyone was crying and asking the remissions of sins. At one hour in the night, a fire vent opened near the hospital in the place called ‘La fumosa’ in the middle of the sea, ejecting a great amount Figure 5. The cone of Monte Nuovo was formed during the 1538 eruption of Campi Flegrei, and destroyed the village of Tripergola. Presently it is completely surrounded by buildings. Photo: Roberto Scandone, Lisetta Giacomelli. Copyright© Nuova Cultura Italian Association of Geography Teachers 30 Roberto Scandone, Lisetta Giacomelli of pumices and rocks. Such vent then progressed toward land and completely destroyed the castle of Tripergola, which was, then filled with sand and rocks making a new mountain, as is seen today (30 July of 1587)”1. The eruption of Monte Nuovo erupted less than 0.1 km3 of magma but substantially changed the morphology of the area and affected an area in the order of tens of square kilometers (Figure 5). Overall the eruption may be classified as a mild explosive eruption. 5. The eruption of Vesuvius in 1631 The great eruption of 1631 is the largest explosive eruption of Vesuvius since those of 79 A.D., and 472 A.D. It occurred after at least 131 years of quiescence. Large trees covered the Gran Cono, the cone within the Somma Caldera, and local people did not remember it being a volcano. The mountain was called “La Montagna di Somma” (the Mountain of Somma, a small town on its northern side). Several months before the beginning of the eruption, people near the volcano felt some earthquakes (Braccini, 1632). They were not particularly scared because earthquakes from the nearby Apennine chain were often felt in the area (a large one had occurred three years before in Apulia, in 1628). The seismic activity became more severe in the few days before the eruption. A violent seismic crisis was felt during the night between 15 and 16 December 1631. A strong explosive eruption started in the morning of 16 December 1631 with a sustained eruption plume, which dispersed pumice and ashes to the NE. The paroxysmal occurred on the following day with the emission of pyroclastic flows, and mud-flows that destroyed all the villages in the immediate surrounding of the volcano. The number of casualties is reported as 4,000 deaths and a lesser number of injuries. Besides the overall destruction of numerous villages and people, also extensive loss of cattle, and arable land is reported. The relative large number of casualties (approximately 10% of the overall population) is to be ascribed to the poor planning of rescue operations. Actually in the night before the eruption, the seismic crisis scared most people in the vicinity of the volcano and also in Naples (Figure 6). Most people around the volcano fled toward Naples, but were forbidden to enter the city because of fear of the plague. Even if the order was revoked, and more than 40,000 people were allowed to enter into Naples, more than 4,000 were reported killed during the major paroxysmal stage and were engulfed in the pyroclastic flows (Giuliani, 1632). 1 L’anno 1538 nel giorno di San Geronimo (28 settembre) si sentì in detta città un gran terremoto, il quale allo spesso pigliava e lasciava, e tutta la città si mise in rivolta e quasi tutta disabitata, andando a Napoli e per le campagne chi fuggiva in un luogo, e chi in un altro e pareva che il mondo volesse subissare, e la gente fuggiva etiam nuda e fuggendo esso testimonio coi suoi figli, e sua moglie, ritrovò alla porta di Pozzuoli una donna nominata Zizula, moglie di mastro Geronimo Barbiero, la quale andava in camicia a cavallo di un somiero alla maniera mascolina scapellata e tutti piangevano e gridavano misericordia. E come fu verso un'ora in due di notte uscì una bocca di fuoco vicino al detto ospidale, nel largo nominato ‘La Fumosa’ da centro mare, e menava gran moltitudine di pietre pomici e di arena, e venne detta bocca di fuoco così aperta ad accostarsi al castello di Tripergola e tutto lo sconquassò, e rovinò, e poi lo riempì di arena, di pietre e vi fece una montagna nuova in 24 ore dove in fino ad oggi si vede” (30 luglio, 1587). Copyright© Nuova Cultura Figure 6. Drawings of the eruption of Vesuvius of 1631 with people escaping from the volcano crossing the Maddalena bridge in the proximity of Naples. Source: Private collection. It is apparent from the short review of historical eruptions in Italy occurring after long periods of quiescence that they caused casualties Italian Association of Geography Teachers Roberto Scandone, Lisetta Giacomelli mostly because of the ignorance of the volcanic phenomena, and even in this case the casualties were only a minor fraction of the total population. Most people had sufficient time to flee from the area endangered by the volcano because of the earthquake activity before the beginning of the eruption. The escape to a distance of 10 to 15 kilometers from the volcanoes was sufficient to prevent any loss of life. The awareness of precursors and the gradual buildup of volcanic activity are the reasons why, also on a planetary scale, volcanic eruptions have caused a limited number of casualties unlike earthquakes, tsunamis and floods. In many cases, the escape from the effect of a 31 volcanic eruption has been made also during the early phase of the activity. In the last 300 years only a few eruptions have caused a large number of casualties as shown in Table 1 (after Blong, 1984, Simkin and Siebert, 1994). In one case (Tambora), the eruption was of an extremely large size and caused extensive damage on a local scale on the island of Sumbawa, and prolonged climatic effects on the planetary scale like also the Laki eruption. The eruptions of Krakatau and Unzen caused a tsunami that was responsible for the majority of casualties. The casualties in the relative lesser magnitude events of Pelée and Ruiz were caused by an under-evaluation of the effects of the eruption. Volcano Year Casualties Cause Laki (Iceland) 1783 Unzen (Japan) 1792 14,524 70% Landslide, 30% Tsunami Tambora (Indonesia) 1815 92,000 90% Famine Krakatau (Indonesia) 1883 36,417 90% Tsunami Pelée (Martinique) 1902 29,025 Pyroclastic Flows Ruiz (Colombia) 1985 23,080 Mudflows 9,350 Famine Table 1. Eruptions responsible for the largest number of casualties in the last 300 years 2010. Source: Scandone and Giacomelli, 1998. 6. Education and planning for a volcanic emergency In Italy, the current planning of the Department of Civil Protection for a volcanic emergency (available at http://www.protezione civile.gov.it/jcms/it/view_pde.wp?contentId=PD E12771 for Vesuvius volcano), is based on the evacuation of the endangered areas as soon as the monitoring network detects any unrest which is likely to lead to an eruption. Unfortunately there is no specific formula that makes it possible to work out a realistic threshold above which an eruption is absolutely certain. Furthermore, the high number of people living in the area makes the evacuation order unlikely to be issued long in advance, because of the economic costs in case of failure of the forecast. Copyright© Nuova Cultura Most past and recent examples suggest that clear signs of an impending eruption may be observed only in the hours before the outbreak, thus making any planned, large scale, evacuation unlikely to succeed. Moreover, the size and character of an impending eruption are completely unknown, and, at the moment, there is no known relationship between the character of precursors and the character of the following event if any (explosive or effusive) so there is great uncertainty as to whether the total evacuation of the area surrounding the volcano is necessary or is underestimated. The current planning has a second major flaw, as the alleged capability of State Agencies to deal with disasters generates a false sense of security in people thus reducing the individual response to natural hazards, as for example, has Italian Association of Geography Teachers 32 Roberto Scandone, Lisetta Giacomelli been observed during the seismic crisis of 2009 at L’Aquila in Abruzzo (Italy). The result of this has been a growth of the urban settlements in the volcanic area without any self-control. For many years scientists have warned the civil authorities of the potential risk of volcanic activity in the Neapolitan area, even if in their efforts they may have over-emphasized the true relevance of volcanic phenomena, thus creating a syndrome of an inescapable catastrophe and the need for strict measures to prevent it. Planning for emergency should be carried out by State Agencies, which should clearly state the real effect of volcanic activity, and the measures that can be taken by individuals to reduce the risk. At the same time, the possible failure of emergency planning has to be presumed, and the rules for behavior be suggested for individuals that may find themselves within an area already affected by volcanic phenomena. This line is far from being attained, as it requires a specific preparation not only of citizens, but also of Civil Protection officials and scientists, with an open admission of the limits of knowledge regarding forecasts on natural hazards. Environmental education in primary and secondary school may help to overcome this divide, but it is often difficult to maintain a balance between the credibility of public institutions and individual actions, as the two may sometime conflict, especially during a crisis. 7. Conclusions The basic principles that should be conveyed to the people living in a volcanic area are about the nature of volcanic phenomena, their effects and the distance at which they are relevant. People should have knowledge of the area where they live and of the necessary measures that should be taken in case of unrest, not only by the Civil Protection, but also by individuals. They should know the forecast limits and be ready to adopt individual escape measures in case of failure of prediction. Preventive measures taken by State Agencies should convey the clear limits of forecasts concerning the size of an impending event, the Copyright© Nuova Cultura duration of precursors and the timing of evacuation. Alternative plans should allow not only a mass evacuation of the area before the eruption, but also the possibility of the total failure of the planned measures, and the rescue of a disordered mass of refugees during the early phases of the eruption. References 1. Blong R.J., Volcanic Hazard, Sidney, Academic Press, 1984. 2. Braccini G.C., Dell’Incendio fattosi al Vesuvio a’ XVI Dicembre 1631, e delle sue cause ed effetti, Napoli, Roncaglioli, 1632. 3. Cigler B.A., “Post-Katrina Hazard Mitigation on the Gulf Coast”, Public Organiz. Rev., 9, 2009, pp. 325-341. 4. Cubellis E., Luongo G. and Marturano A., “Seismic hazard assessment at Mt. Vesuvius: Maximum expected magnitude”, J. Volcanol. Geoth. Res., 162, 2007, pp. 139148. 5. Fournier d’Albe E.M., “Objectives of Volcanic Monitoring and Prediction”, Journ. Geol. Soc. Lond., 136, 1979, pp. 321-326. 6. Giacomelli L., Perrotta A., Scandone R. and Scarpati C., “The eruption of Vesuvius of 79 AD, and its impact on human environment”, Episodes, 26, 3, 2003, pp. 234-237. 7. Giuliani G.B., Trattato del Monte Vesuvio e de’ suoi incendi, Napoli, Longo, 1632. 8. Parascandola A., I fenomeni bradisismici del Serapeo di Pozzuoli, Napoli, Genovese, 1947. 9. Pesaresi C., Marta M., Palagiano C. and Scandone R., “The evaluation of ‘social risk’ due to volcanic eruptions of Vesuvius”, Natural Hazards, 47, 2008, pp. 229-243. 10. Scandone R., “Il rischio da colate di lava e implicazioni socio-economiche”, Atti del convegno “I Vulcani Attivi dell’Area Napoletana”, Napoli, 1977, pp. 103-106. 11. Scandone R., Arganese G. and Galdi F., “The Evaluation of Volcanic Risk in the Vesuvian Area”, J. Volcanol. Geoth. Res., 58, 1993, pp. 261-273. 12. Scandone R. and Giacomelli L., Vulcanologia: Principi Fisici e Metodi di Indagine, Italian Association of Geography Teachers Roberto Scandone, Lisetta Giacomelli Napoli, Liguori, 1998. 13. Sigurdsson H., Carey S., Cornell W. and Pescatore T., “The Eruption of Vesuvius in A.D. 79”, Nat. Geog. Res., 1, 1985, pp. 332387. 14. Simkin T. and Siebert L., Volcanoes of the world (II edition), Tucson, Smithsonian Institution, Geoscience Press, 1994. Copyright© Nuova Cultura 33 15. Wharton Risk Management and Decision Processes Centre, Managing large-scale risks in a new era of catastrophes: Insuring, mitigating and financing recovery from natural disaster in the United States, Philadelphia, University of Pennsylvania, Wharton Risk Management and Decision Processes Centre, 2008. Italian Association of Geography Teachers