volcanic risk zoning in the island of ischia (italy) · archipelago. as other active volcanic areas...

Volcanic risk zoning in the island of Ischia (Italy)

M. Matteral, J,F. Martfn-Duquel, J. Pedrazal, M.A. Sanzl, R.M.Carrasco2 & J.M. Bodoquel‘ Univemidad Complutense, Spain2 Universidad de Castilla-La Mancha, Spain

Abstract

Ischia constitutes the largest and more populated island of the Neapolitanarchipelago. As other active volcanic areas along the middle-west Italian coast(Somma-Vesuvius and Phlegrean Fields), the volcanic activity of Ischia stemsfrom deep fractures associated with the Tyrrhenian sea-floor spreading over thelast 10 million years. The record of historic eruptions along with signs of thermalactivity show that there is a potential for hazardous volcanic events.

The paper constitutes a first approach to the zoning of the volcanic risk of the

island, by considering the three main factors involved — the elements at risk, orvalue (population), the hazard posed by the volcanic phenomena, and the degreeof damage resulting from the hazard (vulnerability). The analysis of the hazardwas carried out by using Geographic Information System (GIS) techniques anderuptive models. The analysis was based not only on the evaluation of theprobability of occurrence of a fiture new eruption within the island, but also onthe evaluation of the probability of occurrence of different intensities andtopologies. As those topologies have different energy and potential fordestruction, they also condition the vulnerability of the value, which is differentfor each volcanic phenomenon. The results show lower volcanic risk levels thanfor similar volcanic areas, However, if two characteristics of the analysed

territory are taken into account —the high tourist affluence and the insularity-,then the risk shouldn’t be underestimated.

1 Geological and vulcanological setting of Ischia

The island of Ischia is located northwest of the gulf of Naples (figure 1). Thevolcanic activity of the Neapolitan archipelago is related with the recentgeological evolution of the Tyrrhenian Sea. About 10 million years ago, the

© 2002 WIT Press, Ashurst Lodge, Southampton, SO40 7AA, UK. All rights reserved.Web: www.witpress.com Email [email protected] from: Risk Analysis III, CA Brebbia (Editor).ISBN 1-85312-915-1

16 Risk Analysis III

Italian peninsula and the islands of Corsica, Sardinia and Sicily were boundtogether. Since then, a process of sea-floor spreading formed the Tyrrhenian Sea,determining an anticlockwise rotation of the Italian peninsula. This movement,still in progress, has generated the stretching of the crust and the formation ofdeep faults, favouring the outflow of magmas to the surface.

Ischia has been formed by different pyroclastic eruptions and effimiveactivity, Absolute dating and volcanological studies have allowed to summarizethis activity in five main phases, accurately studied and described by Vezzoli [1].

Different from sole volcanoes, Ischia doesn’t show an only vent — previouseruptions are aligned to fault-associated centres. This circumstance wasimportant for the hazard evaluation, which focused not only on the absoluteprobability of occurrence of a new eruption, but also on the spatial probability of

formation of new eruptive centres —and their possible eruptive topologies-.

Figure 1: Digital Elevation Model of Ischia obtained from a grid of 10 m. Thefigure shows a superimposed one-square-kilometre grid (UTMcoordinates, map n“ 183 of the Italian Military Geographic Institute,scale 1:25 ,000), to which several calculations will be referred to.

2 Methodology

Despite there are numerous procedures developed for the evaluation of naturalrisks, perhaps the most widely accepted by the scientific community is thatproposed by UNESCO [2]. Specifically considered for volcanic risk, Scandoneand others [3] state:

Risk = (Value) x (Vulnerability) x (Hazard) (1)

where: Value, total amount of lives or properties at risk for a volcanic eruption;Vulnerabili&, percentage of lives or goods likely to be lost because of a given


Risk Analysis III 17

volcanic event; Hazard, probability that a given area may be affected by a certainvolcanic phenomenon, Among thew the most difficult factor to evaluate is thehazard, because it includes the evaluation of the probability of occurrence of a

new eruption —with different intensity-, and the evaluation of the probabilityof the different topologies that might occur for each eruption.

2,1 Hazard evaluation

The hazard evaluation was based upon the hypothesis that a future volcaniceruption will take place behaving similarly to previous episodes, Thus, the firststep was the characterization of the volcanic record of Ischia [1], This was donefor the last 55,000 years, which is the age of the main stratigraphic unit of the

island —the Tufo Verde- and the beginning of the present volcanic dynamics,The second step was to assign the Volcanic Explosivity Index (VEI) of Newhalland Self [4] to each eruptive episode. For this, the volumes of each eruption were

evaluated, and the type of eruption —from the characteristics of the deposits

[1]— were deduced, as they are the main factors which allow the assignment of aVEI. The volume evaluation was carried out by the measurement of a three-dimensional representation of the different volcanic units (by using both theSurfer 7.0 and CartaLinx 2.0 software), Results are shown in table 1,

Table 1. Volcanic eruptions in Ischia for the last 55,000 years and associatedVEI [4]. (+) cubic meters; (*) thousands of years.

EPISODE VOLUME (+) VEI AGE (*) EPISODE VOLUME (+) VEI AGE (*)

Tufo Verde 6040421764 6 55,00 S,Anna 65889405 3 22.60

Pietre Rosse 1537937600 5 46.00 Costa Sparaina 44729669 3 4,00TtiI del Giglio 1510000000 5 33,00 C.s Costalrzo 32638920 3 38.40

Piano Liguori 1103815279 5 5.50 Schiappa and Pomicione 21897696 3 24,00

Selva de] Napolitano 695314783 4 10.00 Pilaro 17391059 3 25,00

Unkrrown centers 386421760 4 3,10 Ciglio and Cava Pelara 13701178 3 23.00

Puuta Irqeratore 272666079 4 19.00 Monte Cotto 11942697 3 28.00

Cantariello 232410831 4 5,00 Monte Vezzi 11048663 3 27,00

Camotese 225207245 4 17.00 Monte Trippodi 9299688 2 1.80

S. Montano 99000000 3 34.00 Vatoliero and others 7972679 2 1.70

Zaro 96249528 3 6.00 Rotaro III 7559731 2 1,70

Bosco dei Conti 94806104 3 2.50 Punts dells Carrrumia 7226958 2 4,50

Upper Cava Pelara 91452237 3 20,00 Lower Cava Pelara 5875222 2 24.00

%arrupo di Parrza 91183976 3 24.00 Catieri 3467587 2 15.00

Rotaro I 91093313 3 2.10 Rotaro IV 2898951 2 1.61

Montagnone I 86082744 3 2.70 Rione Bocca 2736900 2 2.40

Grotta di Terra 85499103 3 19,50 Monte Tabor 984127 1 3.50

Rotaro II 83253603 3 1.80 Porto dkhia 908138 1 2.30

Montagnone II 73218441 3 1.90 Castiglione 795491 1 2.80

Arso 68307999 3 0.70 Grotta del Mavone 557234 1 29,00

Once the VEI was assigned to each episode of the volcanic record, theprobability of occurrence for each VEI was evaluated. For the statistics ofvolcanic eruptions, it is classical the distinction between volcanoes “without



memory” and “with memory” (Wickman [5]), For the former, the number oferuptions in a given time interval has a pattern that follows the Poisson

distribution — the probability of occurrence of an eruption within a time intervalis independent of time. Ischia behaves like volcanic areas with memory, wherethe probability of occurrence of an eruption is not independent of time, becausethe larger the volume of an eruption, the longer the time between an eruption andthe next,

For these situations, the Poisson distribution can not be applied directly, butsubdividing the volcanic activity in different VEI classes, Then, the probabilityof eruption for each VEI can be generalized according to a Poisson distribution,Specifically, for explosive volcanoes, the relationship between the frequency andeach VEI has an exponential pattern (Scandone and Giacomelli [6]):

where: Q is the eruption frequency per year; a is an eruptive fi-equency index ofthe volcano; and b represents an index of the style of activity of the volcano.This relation can be expressed similarly to the Gutenberg-Richter equation [6]:

logo = log(a) -b* J“H (3)

where: b is now a coefficient that represents the slope of the regression line

established for VEI 2 2. Eruptions with VEI < 2 are not considered in theanalysis, because it is assumed that they are underestimated in historical records,Actually, table 1 shows clearly how the number of events of VEI <2 decreasesnoticeably with time. For this reason, to calculate the frequency for each VEI, adifferent time span was considered. By implementing the frequency results foreach VEI in the relation (3), a simple regression was established betweenfrequencies and VEI classes. Results are shown in figure 2.

0.01

I0.001

0.0001

t’= ‘w

n = -1.96016983= y = -1.96016983-0,46014296x

~ = .0,46014296

1 \ ‘-squued=0998074@= l,096~l@ ~ Jo-(o 4614”~U

Figure 2: Mathematical development and fashion of the simple regressionbetween eruptive frequencies and VEI classes.



With this relation, the Age-Specific Eruption Rate (ASER) for each VEI wasobtained. Then, the eruption probabilities (10 and 100 years) for each VEI(probability of observing n eruptions for a given t time) were calculated (table 2).

Table 2. ASER and VEI eruption probability. The probability of observing n

eruptions for a given ttime is defined by: P(O,QVEI = exp (- cD*O.

VEITime interval Number of Age-Specific I m,, , n, I r,, , .nfi.

(years) eruptions Eruptior

1 4,500 3 0.0037!2 5,000 6 0.001316873 20,000 10 0.0004:4 W7nnn 5

, 4--I .. ,”..

5 55,000 I J I V.uuvu

6 I 55.000 I n nnon. . .. . .

r(l.lu)v~~n Rate

r(l.l UU)VEI

‘9915 0.03657522 0.259831290.01299642 0.11543884

5646 0.00454381 0.043609280.00015822 0.00157970 0.00155736r!r,rmr15440 0.00054810 0.00545400......1901 0.00019006 0.00189739

2.2 Spatial favorability for new eruptive centres by means of GIS analysis

As it has been already pointed out, Ischia doesn’t have a preferential vent, Forthis reason, the whole territory of the island is subject to the formation of a newcrater. The objective of this epigraph is the evaluation of the spatial probabilityfor the occurrence of a future eruptive centre. The evaluation was referred to agrid of 10xl O m (raster map), and the GIS utilised to perform the analysis wasIdrisi 32,

The basis for the evaluation were different signs of potential volcanic activity.This information was compiled from various bibliographic sources, In all cases,

deterministic approaches were followed — a zoning of the territory, for eachsign, as a fimction of the tendency of each pixel to favour a new volcanic event.The methodology varies with the sign type, considering their specific conditionsand dynamics.

2,2.1 Distance analysis — fault conditioning and hydrothermal activity

Due to the close relationship between volcanic eruptions and both factors, asreflected by the eruptive history of the island, a distance analysis was carried outfrom both faults and hydrothermal sites (Vezzoli [1]). By plotting the fault andhydrothermal distance maps with the topological location of all the eruptive

centres occurred within the island in the last 55,000 years, new maps —showingthe distance of both factors with respect to the eruptive centres— were obtained.Through the analysis of the histogram obtained from both resulting images, themathematical fimctions that fitted with the pattern, and the establishing of themathematical-statistic parameters that define those fimctions, were recognized.

Once these algorithms were obtained, they were implemented in the digital

base map —through the image calculator and reclass modules—, obtaining therespective propensity maps for both factors (figures 3A and 3B), Calculationlimitation of Idrisi 32 required to break the initial fimction down into severalcompounds, and each one was expressed by means of the algorithms consideredto be more accurate,


2(I Risk Analysis III

2.2.2 Anomalies analysis — gravity, radon and magnetic anomalies

The starting point for the gravity, radon and magnetic anomalies analysis was thedigitisation of the contour lines corresponding to the different values for eachfactor. This was carried out by using the CartaLinx 2,0 software, and fromexisting data sources (Nunziata and Rapolla [7], Maino and Tribalto [8]). Fromthe contour maps, the corresponding digital terrain models (through theconversion tools of Surfer 7.0 and Idrisi 32 software) were obtained. From thedigital terrain models, the corresponding slope maps (expressed in radians) werederived, These maps show the spatial variation of the Z values for each anomaly.

The figures of these maps were later standardized — the total sum of the pixelswas made equivalent to 1 (or 100 ‘XO), and the obtained figures were

recalculated. By these procedures, propensity -or favourability— indexes wereobtained (figure 3C, 3D and 3F). They show the relative probability to theformation of a new crater, based on the information provided by each factor.

2.2,3 Mogi analysis

During its recent geological history, Ischia has undergone vertical movements.Maino and Tribalto [8] (see [9]) studied the evolution of this phenomenon for theperiod 1913-1967. This information was analysed by adapting to this particularsituation the model proposed by Mogi [10]. Mogi’s model links the depth~ of a

magmatic chamber of a radius r with the vertical deformations Ah recorded inthe land surface d. From [8], a digital model of vertical movements wasproduced. Once the point of maximum aptitudinal variation was located, the

average values of vertical deformation Ah for different ranges of horizontaldistances to that point were established. By plotting these data in a Cartesiandiagraw a curve was drawn, Then, the parameters for the polynomial curve ofsecond order that fitted with the fashion of the curve were established, Thisallowed us to establish the depth to which the magmatic chamber would be

situated ~= 2,750 ~ 250 m), The variation in the vertical deformation Ah relatedwith the horizontal distance was expressed by a function of normal distribution,which higher value corresponds with the distance d, By a process of

standardization (the total sum of the values was made equivalent to 1 --or 100

%--, and then the values were recalculated) a zoning of the island, showing thepropensity for the formation of a new crater -considering the signs supplied by

elevation variations- was obtained. The results (relative probability) are shownin figure 3F.

2.2.4 Data integration

Figure 3G shows the integration of all the favorability indexes. The final data,referred to the grid subject to analysis (985 x 776), were simplified andconverted to the grid of figure 1. To make this calculation, it was considered that

the sum of all the probabilities values had to be one — it is to say, that in casethat an eruption will occur, there is a 100% of probability that it will occur in oneof the cell of the island. Giving the same weight to each factor, the sum of eachmap had to be 1/6. Figure 3H shows the simplification of the results.



H

—

Fismre 3: A to F. favourabilitv indexes for the formation of a new eruptive centre–e

by considering the ~nformation supplied by different volcanic signs, A)Faults. B) Hydrothermal activity. C) Gravity anomalies. D) Magneticanomalies. E) Radon anomalies; F) Mogi analysis. G) Hazard zoningby integration all the favorability indexes. H) Simplification andconversion to the one-square-kilometre grid (see figure 1).



2.3 Hazard zoning of eruptive topologies by means of simplified modelling

A simplified hazard zoning of the different eruptive topologies likely to occur in

Ischia -pyroclastic flows and falls, and effusive activity— was made. It wascarried out by a modelling of the different phenomena by: (a) considering thephysical mechanism of each eruption type; (b) taking into account the specificparameters for each VEI class; (c) referring them to a one-square-kilometre gridof the topographic map (see figure 1). The probability, for each eruptivetypology t,was evaluated by the following expression:

(4)

where: k is the number of events with a probability of formation of a new craterPc, which, on the bases of the modelling, reach the cell i.

2.3,1 Pyroclastic flows hazardPyroclastic flows are one of the most damaging volcanic processes [6]. Asconsidered here they include other phenomena, like surges and blasts.

Simulations were carried out for eruptions of VEI >3, because eruptions with alower VEI don’t produce pyroclastic flows. Also, eruptions with VEI >6 areconsidered to affect to the whole island, regardless of where they occur,

For simulations of eruptions with VEI between 3 and 5, the concept of“energy cone”, as proposed by Sheridan [11], was essential. In this model (figure4) it was considered that the distribution of the area of influence of pyroclasticflows would take place within the extent of the circumference of the cone. Theparameters that define the shape and dimensions of the cone depend on both theVEI and the elevation of the crater, For this reason, the minimum height ofcollapse of the eruptive column H,Ol of a pyroclastic flow (for each VEI) is thesum of the height of the energy cone OV, plus the average altitude of the cell.The collapse height of an eruptive column, as a fimction of the volumetric flow

O, is given by [12]:

HCO,= 2.9043+ 0°5’87 (5)

According to Siebert and others [13], if the angle 5 (figure 4) —friction angle-

has a value of 6°, it is possible to calculate for each VEI —through a simple

trigonometric relationship- the circumference radius of the basis of the cone,The energy cone was superimposed to the topography, considering that it is

situated in the middle point of each cell of the grid, This process revealed thoseareas non vulnerable, for being out of the reach of the pyroclastic flows, eitherbecause of their altitude or because they are protected by natural barriers,

By adding the probability values for each class of VEI, the total probabilityof pyroclastic flow hazard was obtained. Results are shown in figure 4.

2,3,2 Pyroclastic fallout hazardWith this expression, we refer the hazard posed by those volcanic materials that,propelled by eruptive Plinian columns, fall out from the air by the gravity effect,



Energy cone (Sheridan [11])

@ Hx w“~~ (vohunetic (heightof the eruptive (cone

flow) collapsecone) radius)

3 105.7 32,6 310.24 1681.8 136,9 1302,5

5 65695.6 916.0 2751,26 262376.3 18411 17516,9

Hazard map

I 14m.40.. .’0. ,01,. <6,0. ,0.. ‘!.. ,!,0. ,),,.

Probablllty

Figure 4: Pyroclastic flow hazard. Physical model, dimensions of the energycones used for simulations, and hazard zoning.

Spatial distributions of fallout deposits have an elliptic shape, with thevolcano occupying one of the ellipse focus, and the major axis facing thedirection of the prevailing high winds. In the proximities of the volcano,pyroclasts fall is not conditioned by winds, so that the deposits distribution is notelliptic but concentric to the crater (see figure 5). Considering this physicalfallout pattern, the hazard evaluation was based on simulations for eruptions of3,4, 5 and 6 VEL

Figure 5 shows the physical model for the simulations, and the geometricalparameters of the corresponding ellipsoid for each VEI class. Those parameterswere calculated by analysing the volcanic record (eruptions of Baia, PomiciPrincipal and Tufo Giallo, to which VEI values of 4, 5 and 6 were assignedrespectively). The ellipse circle and the evaluations are referred to deposits witha thickness higher than 1 metre.

In each simulation, the eruptive centre was located in the ellipse focus, andsuperimposed to the topography. The maximum length of the ellipse wasestablished considering the influence of the prevailing high winds (> 5,500 m forVEI = 3; >12,000 for VEI > 4), By applying (4), the modelling was carried out.Results appear in figure 5.

2.3,3 Effusive activity hazardThe maximum distance that lava flows can reach depends on the emission rateand on the topography through which they flow, The parameters needed forthose simulations were obtained from trigonometric relations and from theanalysis of the geometry and dynamics of two historical eruptions, Rotaro III andArso [1] [14], with VEI 2 and 3 respectively, Higher VEI classes don’t producesignificant lava flows. For these simulations, the model proposed by Walker [15]was followed,



I Geometry of the distribution of pyroclastic falls I Hazard map

‘“~

Figure 5: Pyroclastic fallout hazard, Physical model, dimensions of the ellipsoidsused for the simulations, and hazard zoning.

In Walker’s model, lava flows geometry depends on their chemistry.

Geometry is defined by H —horizontal spreading in terms of the circle diameterwhich surface is equivalent to the lava flow— and by V —average thickness of

the lava flow-. The rate between both parameters defines the “aspect ratio”.Calculations of the aspect ratios for the considered VEI classes were carried

out according to existing studies [1] [12] [14]. These calculations allowed us toestablish specific values of the geometrical parameters, By adding the probabilityvalues for each VEI class for each cell of the grid, it was possible to obtain thetotal probability of lava flows reach for the whole island (figure 6).

2.4 Value and Vulnerability

On the basis of total number of inhabitants living in the island from 1951 to1991, human lives have been the value (1) considered for the risk zoning.Therefore, vulnerability (1) was estimated in terms of percentage of lives likelyto be lost by the different topologies of volcanic phenomena. The most commonestimations for this index are the mortality rates due to different volcanicphenomena in recent times, as reflected by the literature [3]. Thus:- New eruptive centres, As assumed, the formation of a new eruptive centre, atany location, will cause the destruction of an area of approximately one squarekilometre. Thus, the vulnerability associated within this extent is 1 (100 %). Torefer it to the different municipalities, the value of l/N (where N is the number ofcells for each municipality) was considered.- Pyroclastic flows. The high virulence and destructiveness of this phenomenonimplies that the survival rate is virtually zero. Therefore, vulnerability can beconsidered 1 within the extent of pyroclastic flows reach.- Pyroclastic fallout. This is one of the less dangerous volcanic phenomena.Deposit thickness of 10 cm can only cause damage to cultivations, whereasthickness of about 1 m can trigger collapses of some roofs. A figure of 0,1 ofvulnerability was considered for potential deposits thicker than 1 m.



Figure 6: Effusive activity hazard. Physical model, values of maximum distancesfor the simulations, and hazard zoning.

- Lava jlows (e#usive activiq). Lava flows in Ischia are characterised by a highviscosity, so that the mortality due to this phenomenon is always very low. Basedon similar assessments, a figure of 0.01 was assigned to this process,

3 Results, discussion and conclusion

By considering the three parameters involved in the risk evaluation (1) -by the

sum of the partial risks for each volcanic phenomeno~, the total volcanic riskfor each municipality was calculated (figure 7). Average values are lower thanfor similar and nearby volcanic regions [3] [16]. However, if two characteristics

of the analysed territory are taken into account —the high tourist affluence and

the insularity—, then the risk shouldn’t be underestimated.The high tourist affluence has a severe influence on the elements at risk, or

value. Thus, considering than more than 350,000 tourists visit the island insummer, the total risk would be actually much higher than that shown in figure7. The insularity factor would create problems at the time of implementingevacuation plans regarding a possible volcanic eruption, as the present-daymeans of transport by sea from Ischia would be insufficient.

Total Risk

Municipalities 1951 1961 1971 193.1 1991

B?.mo @ Ischia 1342 1298 1303 1418 1717

I Casamicciola I 536 I 5,98 I 648 I 7,13 I 7.89 I

Forkd%chia 1604 17,52 19,78 23,44 2800

lschia Pono 1801 19,79 24,85 2781 28.52

!-am Amno L56 1,90 2.32 267 298

Serara Fontana 298 3,02 307 337 3.71

Figure 7: Volcanic risk evaluation and zoning of Ischia. Data by municipalities.



Risk reduction and mitigation would imply a simultaneous improvement andrevalorisation of some unique volcanic features, which rather than beingexclusively signs of potential volcanic activity, constitute an invaluable naturaland cultural heritage. While this study is preliminary, it does suggest avenues forfuture improvement: (1) computer-aided quantitative models for the eruptivemechanisms; (2) extend the value analysis to the social-economical situation.

References

[1] Vezzoli, L., (cd). Island of Ischia, Quademi dells Ricerca Scientific n“114, Vol. 10, CNR: Roma, 1988,

[2] UNESCO, Report of consultive meeting of experts on the statistical study ofnatural hazards and their consequences, SC/WS/500, UNESCO: Paris, 1972.

[3] Scandone, R., Arganese, G. & Galdi, F,, The evaluation of volcanic risk inthe Vesuvian area, Journal of Volcanology and Geothermal Research, 58,pp. 263-271, 1993,

[4] Newhall, C.G. & Self, S., The Volcanic Explosivity Index (VEI): anestimate of explosive magnitude for historical volcanisrq Journal ofVolcanolo~ and Geothermal Research, 87, pp. 1231-1238, 1982.

[5] Wickman, F.E., Repose period patterns of volcanoes, V: General discussion on atentative stochastic model, Ark, Mineral. Geol., Paper, 4-5, pp. 351-367, 1966.

[6] Scandone, R. & Giacomelli, L., Vulcanologia, principi jlsici e metodid ‘indagine, Liguori Editore: Napoli, 1998.

[7] Nunziata, C, & Rapolla, A., A gravity and magnetic study of the volcanicisland of Ischia, Naples (Italy), Journal of Volcanology and GeothermalResearch, 31, pp. 333-344, 1987.

[8] Maine, A. & Tribalto, G., Rilevamento gravimetrico di dettaglio dell’isolad’Ischia (Napoli), Bollettino Servizio Geologico d’Italia, 92, pp. 109-123, 1971.

[9] Luongo, G., Cubellis, E. & Obrizzo, F,, Ischia, Storia di un ‘isola vulcanica,Liguori Editore: Napoli, 1987,

[10] Mogi K., Relations between the eruptions of various volcanoes and thedeformations of the ground surface around them Bulletin of the EarthquakeResearch Institute, 36, pp. 99-134, 1958,

[11] Sheridan, M. F., Emplacement of pyroclastic flows: a review. Ash-flow tufls,ed, C.E. Chapin & W.E. Elston, Geological Society of America SpecialPaper 180, Geological Society of America: Boulder, pp. 125-136, 1979.

[12] Mattera, M., Valutazione del Rischio Vulcanico nell ‘isola d’Ischia, Tesi diLaurea, Universit~ degli Studi di Napoli: Napoli, 1995.

[13] Siebert, L., Glicken, H. & Ui, T., Volcanic hazards from Bezymianny andBanday-tipe eruptions, Bulletin of Vzdcanology, 49, pp. 435-459, 1987,

[14] Chiesa, S,, Poli, S. & Vezzoli, L., Studio dell ‘ultima eruzione storicadell ‘isola d ‘Ischia: la colata dell ‘Arso 1302, Dipartimento di Scienze dellsTerra, University di Milano: Milano, 1986,

[15] Walker, G.P. L., Explosive volcanic eruptions, a new classification scheme,Geologische Rundschau, 62, pp. 431-446, 1973.

[16] D’Andrea, M., Valutazione del Rischio Vulcanico nei Campi Flegrei. Tesi diLaurea, University degli Studi di Napoli: Napoli, 1993.


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