impact of the ad 79 explosive eruption on pompeii, i. relations amongst the depositional mechanisms...

Impact of the AD 79 explosive eruption on Pompeii, I.Relations amongst the depositional mechanisms of thepyroclastic products, the framework of the buildings

and the associated destructive events

Giuseppe Luongo, Annamaria Perrotta, Claudio Scarpati �

Dipartimento di Geo¢sica e Vulcanologia, Universita' Federico II di Napoli, Largo San Marcellino 10, 80138 Napoli, Italy

Received 26 February 2002; accepted 24 April 2003

Abstract

A quantitative and qualitative evaluation of the damage caused by the products of explosive eruptions tobuildings provides an excellent contribution to the understanding of the various eruptive processes during suchdramatic events. To this end, the impact of the products of the two main phases (pumice fallout and pyroclasticdensity currents) of the Vesuvius AD 79 explosive eruption onto the Pompeii buildings has been evaluated. Based ondifferent sources of data, such as photographs and documents referring to the archaeological excavations of Pompeii,the stratigraphy of the pyroclastic deposits, and in situ inspection of the damage suffered by the buildings, the presentstudy has enabled the reconstruction of the events that occurred inside the city when the eruption was in progress. Inparticular, we present new data related to the C.J. Polibius’ house, a large building located inside Pompeii. From acomparison of all of the above data sets, it has been possible to reconstruct, in considerable detail, the stratigraphy ofthe pyroclastic deposits accumulated in the city, to understand the direction of collapse of the destroyed walls, and toevaluate the stratigraphic level at which the walls collapsed. Finally, the distribution and style of the damage allow usto discuss how the emplacement mechanisms of the pyroclastic currents are influenced by their interaction with theurban centre. All the data suggest that both structure and shape of the town buildings affected the transport anddeposition of the erupted products. For instance, sloping roofs ‘drained’ a huge amount of fall pumice into the‘impluvia’ (a rectangular basin in the centre of the hall with the function to collect the rain water coming from a holein the centre of the roof), thus producing anomalous deposit thicknesses. On the other hand, flat and low-slopingroofs collapsed under the weight of the pyroclastic material produced during the first phase of the eruption (pumicefall). In addition, it is evident that the walls that happened to be parallel to the direction of the pyroclastic densitycurrents produced during the second eruptive phase were minimally damaged in comparison to those walls orientedperpendicular to the flow direction. We suggest that the lower depositional parts of the pyroclastic currents werepartially blocked (locally reflected) and slowed down because of recurring encounters with the closely spaced wallswithin buildings. Locally, the percentage of demolished walls decreases down-current, which has been interpreted as aloss in kinetic energy within the depositional system of the flow. However, it seems that the upper transport systemby-passed these obstacles, then supplied new pyroclasts to the depositional system that restored its physical

0377-0273 / 03 / $ ^ see front matter < 2003 Elsevier Science B.V. All rights reserved.doi:10.1016/S0377-0273(03)00146-X

* Corresponding author. Tel. : +39-081-5803114; Fax: +39-081-5527631.E-mail address: [email protected] (C. Scarpati).

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Journal of Volcanology and Geothermal Research 126 (2003) 201^223

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characteristics and restored enough kinetic energy to demolish the next walls and buildings further along its path.< 2003 Elsevier Science B.V. All rights reserved.

Keywords: Vesuvius; AD 79 eruption; Pompeii; damage to buildings; destructive impact; Polibius; emplacement mechanisms

1. Introduction

The impact of explosive eruptions on denselyinhabited regions is without a doubt one of thecentral themes in modern volcanology. The objec-tive of these studies is to develope short- andlong-term strategies aimed at reducing the risksassociated with various styles of explosive erup-tions. An accurate evaluation of the volcanic riskis, nevertheless, not an easily achievable goal, as itdepends not only on the exposed development,but also on the cumulative knowledge of thephysical behaviour and the past eruptive historyof the volcano.This paper relates the emplacement of pyroclas-

tic products associated with the well-known Vesu-vius AD 79 explosive eruption to the destructiveevents in the city of Pompeii ; it is aimed at under-standing the impact of the eruption on the urbancentres located around the volcano. The studyexamines the role of the buildings in a¡ectingthe deposition and resultant distribution of thepyroclastic products, including a large-scale studyof the e¡ects of the eruption on the city buildingsand an extremely detailed investigation in the C.J.Polibius’ house, a large mansion located in thecity centre. The studied building was chosen forthe following reasons: (1) the nearby presence ofadjacent outcrops of the pyroclastic deposits ofthe AD 79 eruption; (2) the relatively recent ageof the excavation, assuring excellent preservationof the e¡ects of the eruption; (3) the availabilityof excavation reports containing stratigraphicdata and information about the state of the build-ing, including the restoration techniques adopted;(4) the availability of clear, comprehensive photo-graphic coverage, together with several drawingsand watercolour paintings, documenting the mainphases of the excavation.This research was performed applying a typical

volcanological approach (stratigraphy and litho-facies de¢nition, reconstruction of the emplace-

ment mechanisms) to the study of these archivedphotographs, paintings and documents. This en-abled a detailed analysis of the behaviour of theseurban constructions as they were exposed to ex-treme mechanical and thermal conditions associ-ated with the eruption, as well as evaluated theextent to which the buildings a¡ected the distri-bution and dispersion of the pyroclastic products.In particular, a model for the interaction betweenthe urban structures and the depositional systemof the pyroclastic density currents (PDCs) is pre-sented. A reconstruction of the sequence of eventsin Polibius’ house is also proposed. Finally, ageneral model of the e¡ects of the AD 79 eruptionon the city of Pompeii is discussed.

2. The Vesuvius AD 79 eruption

The AD 79 eruption that destroyed Pompeiiand Herculaneum has been widely studied in thelast twenty years and several interpretations of itsdynamics have been proposed (e.g. Lirer et al.,1973; Sigurdsson et al., 1985; Carey and Sigurds-son, 1987; Cioni et al., 1990, 1992, 1996; Yokoya-ma and Marturano, 1997; Mastrolorenzo et al.,2001). The letters, written by Plinius the Youngerto the historian Tacitus, reporting the dramaticevents formed the starting point for all of them,even the most recent ones.The eruption was preceded by several earth-

quakes. The strongest of them, which severely af-fected the city of Pompeii, occurred in AD 62 andis considered to be directly related to the AD 79event (Luongo et al., 1995). The eruption lasted19 h, from 1.00 p.m. of August 24 to 8.00 a.m. ofAugust 25. It began with a weak phreatomag-matic explosion covering the volcano with anash deposit. Next, a pumice lapilli fall from aPlinian column 14^32 km high (Carey and Si-gurdsson, 1987) covered a large area south ofthe volcano (Lirer et al., 1973). Pumices are white

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at the base and grey towards the top of the de-posit, re£ecting a change in chemical compositionand density of the tapped magma (Civetta et al.,1991). The maximum thickness of the fall deposit(2.8 m) was reached 10 km south of the volcanoin the city of Pompeii (Sigurdsson et al., 1985).Several PDCs were produced immediately before,during and after the fallout phase of the greypumices; they £owed mainly to the north, westand south. Cities such as Herculaneum, thatwere little, if at all, a¡ected by the pumice lapillifallout, were reached by PDCs the emplacementtemperature of which was as high as 400‡C (Kentet al., 1981; Capasso et al., 2000; Mastrolorenzoet al., 2001). The development of a syn-eruptivecaldera structure is possibly evident by the pres-

ence, only to the volcano slopes, of lithic-en-riched, valley ponding £ow deposits (Cioni etal., 1992, 1996). The role of phreatomagmatismduring the course of the eruption is debated.The beginning of magma^water interaction is re-lated to the ¢rst PDC after the fall phase (Barberiet al., 1989; Cioni et al., 1996) or, more probably,to the last stage of the eruption (Sigurdsson et al.,1985), as testi¢ed by the abundant accretionarylapilli and the high degree of fragmentation ofthe particles forming the ¢nal strati¢ed ash depos-it. The emplacement of the PDCs during this lat-ter stage was not continuous, as is shown by thepresence of three lithic-rich fall layers easily dis-tinguishable in the upper part of the phreatomag-matic sequence.

Fig. 1. Plan view of Pompeii showing the location of the Polibius’ house (grey rectangle), the house of the Chaste Lovers andtheir relative outcrops, (a) and (b). Dots represent locations of the other outcrops studied. Roman numbers indicate locations of‘regiones’. Lower part: facades of the two buildings. Inset: sketch map showing the relative position of Pompeii and Mount Ve-suvius.

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3. General stratigraphy of the AD 79 deposit atPompeii

This stratigraphy is based on seven sections lo-cated close to the city walls and inside the city(Fig. 1). A composite section of the deposit ofthe AD 79 eruption cropping out at Pompeiiwith a lithological and lithofacies description isillustrated in Fig. 2. We prefer to use a new de-scriptive nomenclature rather than the previouslyadopted (model-driven) genetic terminology (e.g.fall, £ow and surge layers by Sigurdsson et al.,1985 and eruptive units by Cioni et al., 1996). Acorrelation between the previous stratigraphic no-menclature of the AD 79 deposit at Pompeii andthat used in this study is also illustrated in Fig. 2.The AD 79 deposit consists of a lower white togrey pumice fall bed (units A and B), 2.8 m thick,overlain by strati¢ed ash and pumice PDC layersvariable in thickness from a few decimetres to 3 m(units C^L). This upper sequence is interstrati¢edwith minor, thin and lithic-rich fall layers (unitsD, G and I). The main fall bed (unit A) is grain-supported and is composed mainly of angularpumice lapilli clasts with minor wall rock lithicclasts of volcanic (lavas) and sedimentary (lime-stone) origin. Coarse ballistic blocks, both ofpumice and wall rock nature, are scatteredthrough the bed with a maximum concentrationin the upper grey horizon (unit B). The base ofthe PDCs succession is made up of three very thinlayers (unit C): a couple of massive ash layerswith rare, rounded, ¢ne pumice lapilli interlayeredwith a very thin sandy layer made up by small,rounded pumice clasts. This unit is capped by amassive, 4.5-cm-thick, well sorted fall layer rich inlithic clasts (unit D). The deposit that overlies thisfall layer is a matrix-supported, strati¢ed bed richin rounded pumice lapilli in the basal part withnumerous sedimentary structures (e.g. dunes andcross strati¢cation) towards the top (unit E). Theuppermost part of the sequence comprises a suc-cession of plane parallel ash layers with abundantaccretionary lapilli (units F, H and L) alternatingwith three, very thin, lithic-rich fall layers (units Gand I). The increase of ¢ne ash together with thepresence of accretionary lapilli suggest a changefrom magmatic to phreatomagmatic style of the

eruption in correspondence of unit F. Rare im-pact sags are present at the base of unit G; thelower ¢ne grained ash layer (F) is deformed bylithic fragments up to 9 cm in diameter.The main structural features of the recognised

units are exempli¢ed at the Nola Gate section,where the AD 79 pyroclastic sequence thickensin correspondence of a Roman road enclosed be-tween an embankment that rests on the city wallsand an enclosure wall (Fig. 3). Both the thickcoarse pumice fall layers (units A and B) andthe thin lithic-rich fall layers (units D, G and I)maintain a uniform thickness on the steep slope(25‡) of the Roman embankment. The lower PDCunit (C) shows a relatively uniform thickness onthe slopes (4^8 cm) and thickens in the depression(25 cm). The main PDC unit (E) is topographi-cally controlled, ¢lling the depression. Its lowerlayers are completely con¢ned within the depres-sion (E1), while its upper layers drape the topog-raphy thinning toward both the sides (E2).

4. Stratigraphy inside Pompeii

The most complete stratigraphic sections of theAD 79 deposit inside the city are located a fewmetres from the eastern wall of the Polibius’house, in the garden and immediately west ofthe house of the Chaste Lovers, which is, inturn, located a few metres west of the Polibius’house, i.e. locations (a) and (b) in Fig. 1. Thedetailed stratigraphic reconstruction of these twosections is of absolute importance, even beyondthe objective of the present study, since they rep-resent extremely rare examples of deposits of theAD 79 eruption still preserved in the city of Pom-peii. Most of the previously studied stratigraphicsequences were, indeed, located either outside thecity walls (Sigurdsson et al., 1985; Santacroce,1987; Lirer et al., 1993) or in their vicinity (Ritt-mann, 1950; Di Girolamo, 1964; Cioni et al.,1996; Yokoyama and Marturano, 1997).

4.1. The house of the Chaste Lovers

This outcrop is located in a narrow alley (a fewmetres wide) between two vertical walls on the

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Fig. 2. Left: composite stratigraphic section showing the maximum thickness of the units of the AD 79 deposit at Pompeii. A lithofacies description is also illus-trated. Right: detailed stratigraphic columns along the western side of the house of the Chaste Lovers and in a hole dug a few metres from the eastern perimeterwall of the Polibius’ house. For location of the sections, see Figs. 1 and 4. Inset: relationship between the stratigraphy presented in this paper (TP) and those pub-lished by Sigurdsson et al., 1985 (S) and Cioni et al., 1996 (C).

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western side of the house of the Chaste Lovers(Reg. IX, 12, 5^7). The outcrop is 28 m longand averages 2.5 m in height. The cut strikesN150‡ and is radially oriented with respect tothe vent. The succession is made up of a PDCsdeposit of strati¢ed ash and pumice lapilli over-lying the thick pumice lapilli fall (Fig. 4); the baseof the deposit (white pumice lapilli, unit A) is notoutcropping. Fig. 2 shows ¢ve stratigraphic sec-tions that have been measured in detail from theoutcrop and lateral facies variations. The fall de-

posit (unit B) is not continuously outcropping andits thickness ranges from 0 to 1.2 m. It is massive,composed of grey pumice lapilli and minor lithicclasts (both lavas and limestone) showing a max-imum diameter of 7.5 cm. An easily recognisableerosional surface separates it from a 8-cm-thickunit made up of ¢ne, sub-rounded pumice clastswith increasing ¢ne ash toward the top (unit C). Itis overlain by a massive, well sorted, 6-cm-thickunit formed of angular lithics and minor pumiceclasts (unit D). This whole sequence is covered by

Fig. 3. (a) The complete sequence of the AD 79 pyroclastic deposit at Nola Gate (for location, see Fig. 1). The pyroclastic de-posit thickens in correspondence of a Roman road enclosed between an embankment that rests on the city walls and an enclo-sure wall. (b) Sketch of the geometry of the di¡erent units distinguished throughout the AD 79 deposit. Note the mantling natureof the fall units (A, B, D, G, and I) while the PDC units show di¡erent geometric relationships with respect to the palaeo-topog-raphy. Unit C mantles the topography and thickens in the depression; unit E is valley-ponding, ¢lling the topographic depres-sion. The upper part of the sequence (dotted layer) is made of reworked material accumulated during past excavations (actuallythis material has been removed).

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a 69^115-cm-thick bed showing dunes the averagewavelength and amplitude of which are 15 and0.7 m, respectively (unit E1); they are formed ofalternating layers of ¢ne ash and coarse pumicelapilli becoming thicker and coarser in down-cur-rent direction. The dune pro¢le is symmetric, boththe £anks of the crest dipping around 15‡. If com-pared to subaqueous analogues, these dunes canbe classi¢ed as ‘medium dunes’ (Ramsay et al.,1996). Another, smaller kind of dune that is ¢nergrained, is present in between the crests of the

previous dune system. Their wavelength/ampli-tude ratio is lower (6 vs. 20) and their maximumthickness reaches 35 cm (unit E2; Fig. 5). Theyare comprised of alternating layers of ¢ne andcoarse ash; their crests are cuspate and asymmet-rical, the up-current and the down-current £anksdipping 15‡ and 13‡, respectively. The lee slope isalso concave upward. These dunes are progressivesince their crests tend to migrate down-currenttowards the southeast. Massive and accretionarylapilli-rich ash layers, 16^45 cm thick, overlie the

Fig. 4. Sedimentary structures in the AD 79 deposits close to the house of the Chaste Lovers. (a) Truncated walls of the houseof the Chaste Lovers (foreground); the AD 79 pyroclastic succession (background). (b) Sketch of the stratigraphic successionshowing the main sedimentary structures of the deposits. The wave-shaped boundary line between the basal fall pumice and theoverlying PDCs deposit is worth noting. The progressive crests of the dunes are well evident in the middle part of the sequence.The arrows show the exact location of the detailed stratigraphic sections reported in Fig. 2. The scale changes in this perspective.

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dune beds (unit F). Each bed shows an upwardincrease of the abundance of accretionary lapilli.Above them, two lithic-rich fall levels form acharacteristic couple separated by a 2-cm-thickash layer (unit G). The lithic-rich levels are mas-sive, well sorted and made up by angular clasts ;their respective thicknesses are 4 and 3.5 cm. Atthe top of this unit another ash deposit with ac-cretionary lapilli, 12^15 cm thick, is present (unitH). Overlying this unit there is one more thin (1.5cm), lithic-rich fall level (unit I). Finally, a strati-¢ed ash deposit, 20^62 cm thick, caps the se-quence (unit L): individual beds are massive andcontain sparse accretionary lapilli. The whole suc-cession is locally eroded and channels are ¢lledwith reworked pyroclastic material, 10^90 cmthick (unit M).

4.2. Near the Polibius’ house

This outcrop is located on the eastern side ofthe room [DD] in Polibius’ house; some furtherexcavation was required to obtain better expo-sure. The section is almost 2 m high, but thebase of the deposit cannot be observed. The pum-

ice lapilli layer (unit B), 83 cm thick, is overlainby a 4-cm-thick ash horizon that includes a thin(1 cm) coarse ash unit (unit C). A massive, wellsorted, 5-cm-thick fall bed, mainly formed oflithics and minor pumice clasts (unit D), follows.This part of the sequence ends up with a lens ofreworked material cut into the underlying unitsup to the top of layer B. Above it, the depositis strongly layered and mainly made up ofPDCs products. The ¢rst horizon is made up bywell rounded pumiceous lapilli and subordinateash (unit E1); the lapilli are mainly concentratedin the lower part (thickness ranges from 19 to 38cm). Next, a conformable layered ash horizon,9^16 cm in thickness, is present (unit E2). Thislevel is, in turn, overlain by another ash level,11 cm thick, massive and very rich in accretionarylapilli (unit F). Two thin lithic-rich and wellsorted airfall layers, respectively 3 and 1.5 cm,overlie unit F. They enclose a 1.5-cm-thin ash ho-rizon (unit G). The ¢nal deposit is a layered ashhorizon, 56 cm thick (unit H and L), with a thinlithic-rich level (unit I) located a few centimetresfrom the base. The sequence is covered by themodern soil.

Fig. 5. Unit E2 forming progressive dunes in the central part of the pyroclastic current deposits at the house of the Chaste Lov-ers. Flow direction is from right to left. Scale is in 20-cm intervals

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5. Investigation in the C.J. Polibius’ house

5.1. Location and description of C.J. Polibius’house

C.J. Polibius’ house is located in Via dell’Ab-bondanza (Reg. IX, 13, 1^3), one of the mainroads in the centre of Pompeii (Fig. 1), at a heightof 32 m above sea level ; the ground on which it islocated slopes towards the road. The shape of thebuilding is nearly rectangular, 48 by 18 m, with

the larger side perpendicular to the main road; itsarea is 850 m2 (Fig. 6). The building is boundedby roads on the southern and western sides andby other buildings to the north and east. Two£oors are present: 37 rooms are located on theground £oor and 19 on the upper £oor, the for-mer being identi¢ed by means of one or two cap-ital letter(s) in Fig. 6.For the sake of simplicity, the house can be

subdivided into three zones: front, middle andrear. In the front part two £oors are present:

Fig. 6. Ground £oor plan view of Polibius’ house. Rooms indicated by capital letters. Rooms of which roofs and walls collapsedduring the ¢rst fall phase are distinguished from those of which the building structures collapsed during the emplacement ofPDCs. Note the directions of upsetting of the walls during the two main eruptive phases: random directions in the fall depositand exclusively towards south in the PDCs deposit. The locations of the stratigraphic sections illustrated in Figs. 7 and 11 arealso shown.

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Fig. 7. Stratigraphic sections inside the Polibius’ house showing the pyroclastic succession de¢ned with lithostratigraphic datafrom the excavation reports. The thickness of the distinguished deposits (fall lapilli pumice deposit, strati¢ed ash and pumicePDCs deposit, reworked pumices and soil) change remarkably in the di¡erent rooms. The external pro¢le of the reconstructedbuilding is also reported. Zero height corresponds to the ground level at the time of the excavation; horizontal distance is not toscale. Section traces are reported in Fig. 6.

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the maximum height is about 9 m along Viadell’Abbondanza and 6.5 m towards the interior.Two impluvia are present in this area, a main one[O] and a secondary one [N]. The middle zone ofthe building is a square-shaped garden 100 m2

wide; this is surrounded by a portico on threesides (north, east and south) and bounded bythe 5.4-m-tall perimeter wall of the building onthe fourth side. In the rear zone the upper £ooris absent and the maximum height reached is6.2 m. The roofs are very articulated; accordingto the current reconstruction of the house, noneof them were £at. In the front zone of the house,they were re-built in order to almost completelydrain rain water towards the impluvia [O] and[N]. The roo¢ngs on the northern, eastern andsouthern porticos dip towards the garden; theone on the western side bears a cuspate roo¢ngdipping towards both the garden and the outerroad. Because of the sloping ground towardsVia dell’Abbondanza, the position of the £oorrises toward the rear part of the building. As ageneral rule, the rooms in the front are either atthe same level of [A] or 70 cm higher; in thegarden and the rear zone the £oor elevation is1.2 m.

5.2. Stratigraphy of the AD 79 deposits inside thePolibius’ house

Based on the large number of observations re-ported in the excavation logs, a reliable strati-graphic reconstruction could be made in themajority of the Polibius’ house rooms. The strati-graphic sequence in 29 of the 37 rooms on theground £oor was reconstructed. Fig. 6 illustratesthe rooms for which at least one datum is avail-able. In order to synthetically show the strati-graphic sequence, eight sections were reported(Fig. 7) showing: (1) the £oor pro¢le; (2) theroof pro¢le and the location of the outer perime-ter walls of the house according to the way theywere rebuilt ; (3) the lithotypes observed at thedi¡erent stratigraphic heights ; (4) the position ofthe boundary between the white^grey lapilli falldeposit and the upper strati¢ed ash and pumicePDCs deposit ; and (5) the upper limit of thestrati¢ed ash and pumice PDCs deposit.

With respect to its main features, this sequencelooks very similar to those previously described inSections 4.1 and 4.2: a thick basal pumice depositis overlain by a PDCs succession locally coveredwith reworked material or humus. Nevertheless,the thickness variations observed in the pumicedeposit (1^5 m) are very signi¢cant: the greatestthicknesses are observed in the two impluvia [N]and [O], in the peristyle and the alleys and gar-dens located immediately outside the house (sec-tions 2, 3 and 5; Fig. 7). The overlying PDCssuccession also shows thickness variations (fromfew tens of cm to 4 m). In this case the deposit isthicker where the pumice lapilli fall is thinner andvice versa; an approximately uniform total thick-ness is thus maintained. The reworked material,the thickness of which is also variable, is some-times reported as being incorporated into the pri-mary deposit. This is a case of the reworking tak-ing place during the breaching of walls when the¢rst exploratory wormholes were dug. In othercases, i.e. [II] and [HH], the primary deposit wasalmost totally lacking and only reworked materialwas found. The whole sequence is capped by asoil whose thickness ranges from a few tens ofcentimetres to 2 m. The presence of a peculiarstratigraphic sequence (section 3 and Fig. 7) in[II], [GG] and [HH] is extremely interesting.Here, an ash layer of a few centimetres to 40^50cm thick is directly laid on the £oor. Above it, athick pumiceous deposit probably of reworkedmaterial is present. Along the western wall (stillintact) of the peristyle, dune-shaped bedforms re-lated to the second phase of the eruption areeasily recognised (Fig. 8) : their wavelength isaround 8 m and their amplitude ranges from 30cm for the lowermost to 45 cm for the uppermostone. Their crests do not show any clear up- ordown-current migration, thus implying a station-ary wave. The height of the base of the lowermostdune marks exactly corresponds to the boundarybetween pumice fall and PDCs deposit as de-scribed in the excavation books.

5.3. State of the objects found

A remarkable number of objects were foundduring the excavations in the building. A thor-

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ough analysis of all of them would be far beyondthe aim of the present research. Rather, it wasdecided to focus our attention on those fragileobjects such as glasses and earthenware, the con-dition of which was a good indicator of the ther-mal and mechanical stresses during the di¡erenteruptive phases and the burial of the house. Sev-eral amphorae crushed by a big fallen roof werefound on the £oor of [A], amphorae and otherearthenware were found intact on the £oors of[TT], [C], [UU] and [BB]: all of them were en-closed in a thick layer of pumice lapilli. Manyother objects, intact or broken, were found inthe pumice lapilli deposit 1^3 m above the respec-tive £oors in rooms [D], [N], [G], [A], [R], and[BB]. Earthenware, mainly in fragments, werealso found in the PDCs succession. The objectscontained in 5 closets located under the roofalong the eastern wall of the peristyle formed anextremely interesting discovery. The lower part ofthe closets was buried under the pumice lapilliand the upper part under the ash and pumicePDCs deposit. The wood slowly rotted out duringthe centuries leaving several astonishingly wellpreserved objects in the hardened ash and pumi-ces: bottles, jugs, dishes, jars, glasses and severalearthenware pieces. Most of them were intact andperfectly preserved.

5.4. Carbonised wood and traces of ¢re

Remains of carbonised wood were found in thefront part of the house. They mainly consisted ofroofbeams supporting the ceiling of the ground£oor and, to a minor extent, tables or doorposts,still in place or collapsed to the ground. All ofthese remains were found preferentially withinthe fall pumice and only rarely within the PDCsdeposit. The condition of the plasters and frescoeson the walls of the ground £oor ruled out thepossibility that great ¢res took place during orimmediately after the eruption. Only the walls ofroom [Z] were entirely covered in soot, probablyas a result of local combustion. In addition, somestudies carried out on the glasses found in thebuilding revealed that only in one case (bottleneckfrom closet IV in the peristyle; Verita' et al., 2001)the temperature reached a value su⁄ciently high(620‡C) to completely deform the object.

5.5. Skeletons

All of the recovered skeletons were found inrooms [GG] and [HH] in the rear of the building,the only exception being two human skulls com-ing from the upper part of the pumice lapilli de-posit (probably locally reworked) in the peristyle.

Fig. 8. Left: picture of the western wall of the peristyle. The marks of two wavy surfaces can be observed above and below theroo¢ng testifying to the presence of dunes from a typical pyroclastic current deposit. Right: reconstruction of the boundary be-tween the fall pumice and the strati¢ed PDCs deposit. The marks left by the pyroclastic currents deposit in the western wall ofthe peristyle are reported: it can be observed that the basal mark corresponds to the boundary between the two deposits.

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All of the four skeletons from [GG] (Fig. 9)were lying on an ash layer variable in thickness.The head of the ¢rst (I) skeleton was 30 cm abovethe £oor in the northeastern corner; the remain-ing part of the body was found in the northwest-ern corner, partly directly on the £oor and partly30 cm above it. The second (II) and third (III)skeletons were lying on the £oor, respectivelyalong the western wall and in the middle of theroom. The fourth (IV) skeleton was found alongthe eastern wall ; the legs and the rest of the bodywere respectively 20 and 40 cm above the £oor.Seven skeletons were recovered in [HH]. The

¢rst (I) skeleton, located along the northernwall, was lying above some tiles and other ceilingdebris ; it was buried into a mixed deposit of ash,pumices and stucco fragments from the ceiling.The second (II) and third (III) skeletons were onthe £oor in the northwestern corner; they werecovered with pumice lapilli and ceiling stucco.The fourth (IV) skeleton was found along thewestern wall, 40 cm above the £oor. The ¢fth

(V) and sixth (VI) skeletons were in the middleof the room, lying on a thin ash layer and understucco fragments from the ceiling. The seventh(VII) skeleton consists of the small bones of afoetus found in the abdominal region of themother’s skeleton (II). Some casts were foundwithin the ash deposit. They are related to sometables, probably beds, located along the northernand western wall in [HH]. Skeletons (I) and (IV)may originally have been lying upon them.

5.6. Collapses

A great amount of debris from walls and roofswas found. According to the excavation reports,collapses during the eruption lowered the averageheight of the walls 3^4 m.

5.6.1. Attics and roo¢ngsAt the moment of excavation, no roofs or attics

were found to be in situ; debris from them wasfound both in the basal pumice fall and the over-

Fig. 9. Some of the skeletons in room [GG]. Skeletons (III) and (IV) are above an ash layer, 20^40 cm thick, lying directly onthe £oor. The skull of skeleton (I) is close to the feet of skeleton (IV).

VOLGEO 2630 21-7-03


lying strati¢ed ash and pumice PDCs deposit (Fig.6). Parts of the roof of [A], [M], [E], and [D], theattic of [Z], and the roo¢ngs of [N] and [G], all ofthem recovered from the pumice lapilli, were lyingon the respective ground £oors; the attics of theupper £oors and the roofs of [C], [B], [H], [SS],[AA], [GG], [II], [HH], and [BB] were found in thePDCs deposit. In particular, the ceiling of [SS]was found to be only 20 cm lower than its originallevel. On the contrary, the western, eastern andnorthern roo¢ngs of the peristyle, buried by thestrati¢ed ash and pumice deposit, were found stillabove the perimeter wall. The roo¢ng on thenorthern side was partially destroyed, but theothers su¡ered very little damage. Only few roof-ing-tiles and bent-tiles were missing from thewestern roo¢ng, whereas the eastern one waspractically still intact. It is important to mentionthat the original level of these roo¢ngs was 2 mlower than the level of those in the front and rearzones of the house. The stratigraphic height of thetiles within the volcanic products in [EE] estab-lishes the timing of collapses of the ceiling in thebuilding. In the western part of the room the ceil-ing was smashed to the ground under the load ofthe pumice lapilli fall deposit, whereas in the east-ern part the cast of a bed headboard bent by thefalling ceiling was observed within the PDCs de-posit. In addition to the roo¢ngs and attics de-scribed above, several tiles, either intact or infragments, were recovered at various stratigraphicheights in all the rooms of the building. For in-stance, fragments of tiles were recovered fromthroughout the whole thickness of the deposit inroom [EE].

5.6.2. WallsNearly all of the walls were found to be partly

or entirely demolished. In particular, only thewestern corner of the facade and the lower partof some inner walls were still in place on theupper £oor. According to the excavation reports,the walls buried in the PDCs deposit had mainlycollapsed southwards, whereas those in the falllapilli did not show any predominant directionof collapse (Fig. 6). It is also worth mentioningthat, as a general rule, the north^south trendingwalls were less damaged than those trending east^west. Fig. 10 shows the average heights of thetransversal walls of the house. Even removingthe topographic e¡ects (sloping ground), theamount of demolition was higher moving fromthe main facade towards the peristyle and thendecreases again in the rear of the building. Fig.11 shows ¢ve transversal cross-sections alongwalls located at increasing distance from the fa-cade of the building. In all of them, a channel-shaped pro¢le of the demolished walls can be ob-served. These pro¢les have di¡erent depths andtheir bases have been measured at di¡erentheights from the ground £oor. The northernmostpro¢le is reported in the excavation reports at thetop of room [EE] (Fig. 11), with its depth lessthen 1 m and its base at the top of the ground£oor (about 6 m height). The middle pro¢le ismore then 6 m deep and its base is a few tensof centimetres above the ground £oor. The south-ernmost one is about 4 m deep and its base isnearly on the upper £oor. These pro¢les largelycorrespond to the boundary between the basal falland the overlying PDCs deposit. Within the house

Fig. 10. Variations in the average height of the east^west trending (transversal) walls in the Polibius’ house; the variations of theground level are taken into account.

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Fig. 11. Sections along some of the transversal walls of the house showing the concave upper pro¢le of the walls. (r) Top ofroom [EE] redrawn from excavation journals. (V), (VI) and (VIII) sections reconstructed during this study. (f) Picture of the fa-cade as found during the excavations. Boundaries between the di¡erent lithotypes are shown for sections (V), (VI) and (VIII).The correspondence between the wall heights and the contact between the fall and the PDCs deposit is worth noting. The loca-tions of the sections are reported in Fig. 6. Legend as in Fig. 7.

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it is important to point out two other intriguingobservations: (1) the transverse walls in the rearof the house were still intact at the time of exca-vation; and (2) the metal hinges of the doors ofthe rear rooms lay on the £oor under the PDCsdeposit.

5.7. Extent to which the roofs and walls a¡ectedthe distribution of the pyroclastic fall deposit

The stratigraphy of the products of the AD 79eruption inside the Polibius’ house is anomalouswith respect to the surrounding areas (Fig. 7), themain di¡erence consisting in thickness changes ofthe fall deposit. Remarkable variations were in-deed observed in the peristyle [CC], in the alleysaround the building, and, as already reported inSection 5.2, in rooms [N] and [O]. Also, the fallpumice deposit in the garden of the peristyle thinstowards the sheltered corridor of the eastern por-tico (section 4; Fig. 7), probably as a result ofpumices rolling down from the thickening heapin the centre of the garden.The present restoration of the building, with all

of the roofs dipping at 15‡ towards both the sur-rounding alleys and rooms [CC], [N] and [O],would explain the additional amount of falloutdeposit as being due to the rolling down of thefalling pumices from the adjacent roofs.Evaluating the exact timing of the roof collap-

ses is not straightforward. If an accumulation rateof 15 cm/h (Sigurdsson et al., 1985) and an aver-age density of 650 kg/m3 are assumed for the fall-ing pumice, an incremental load of 100 kg/m2 perhour is realised. Unfortunately, since no data onthe yield strength of the Pompeii roofs are avail-able in the literature, the critical thickness causingthe collapse cannot be determined. On the otherhand, studies carried out on several recent erup-tive events (Blong, 1984) report roof collapses tooccur with thicknesses ranging 0.1^1 m, a valuewell matched by the 40 cm calculated by Sigurds-son et al. (1985). As a consequence, roof collapsesin Polibius’ house might have taken place 1^6 hafter the beginning of the eruption. On the otherhand, the PDCs deposit belonging to the seconderuptive phase, lying directly on the £oor in manyrooms of the rear part of the house, suggests some

of the roofs be still in place after the end of theinitial pumice fall phase. All of the above dataclearly show that a di¡erent response of the roofsof the building took place during the ¢rst phase ofthe eruption. Those in the front part of the housecollapsed, whereas those in the central and rearzones did not. Since the possibility of di¡erentpumice amounts falling on the di¡erent parts ofthe building can be ruled out completely, it isproposed that the roofs in the front zone weremuch £atter than those in the current restorationof the building and allowed an unusual accumu-lation of the falling pumices, eventually collapsingunder the pumice load. The steeper roofs in therear part of the house and the peristyle allowedthe falling pumices to roll and slide down andaccumulate in the adjacent impluvia and the gar-den, respectively.

6. State of the buildings in the whole city ofPompeii

To investigate the damage su¡ered by thewhole city of Pompeii we evaluated the state ofthe buildings all over the city (Fig. 12a). A limitto this investigation is the partial reconstruction(restoration) of many buildings and the lack ofgood reports from ancient excavations (most ofthe city has been excavated in the past centuries).Our survey shows that the type of destructionsu¡ered by the city can be described in the follow-ing observations:(1) The ground £oor is partly intact in most of

the buildings, whereas the upper £oor is almostcompletely demolished.(2) Most of the destruction is stratigraphically

related to unit E. In fact, as exempli¢ed by therecently excavated House of Chaste Lovers, ma-terial from demolished walls lay inside this unit(Fig. 12b,c) as well as some of the victims ofthe PDCs phase of the eruption (Luongo et al.,2003).(3) The east^west oriented walls are by far more

damaged than those striking north^south.(4) It is still possible to observe a channel-

shaped pro¢le in many of these demolished walls.(5) In many cases, the northern, vent-facing

VOLGEO 2630 21-7-03


part of the buildings was more damaged than thesouthern one (Fig. 12d).(6) The northern (relatively proximal) and

southern (relatively distal) sectors in the citywere a¡ected in the same way.

7. Analysis of the behaviour of the pyroclasticcurrents

A major contribution to understanding thePDCs transport and emplacement mechanismswas provided by comparing large-scale (i.e. wholecity) and small-scale (i.e. building by building)distribution of damages. The distribution and

type of the damages noticed throughout the cityis inhomogeneous although the east^west orientedwalls are more completely destroyed. Locally, amore regular destruction pattern is recognisable;the height of demolished walls decreases towardsouth.Recent studies (Valentine, 1987; Fisher, 1990;

Druitt, 1992, 1998; Freundt and Bursik, 1998;Freundt et al., 2000) and direct observations ofPDCs (e.g. Mount St. Helens and Pinatubo erup-tions) showed that these currents are clouds of gasand volcanic ash tens to hundreds of metres thickthee particle concentration of which increases to-wards the base. In these £ows particles are mainlytransported in suspension by turbulence (trans-

Fig. 12. State of the buildings at Pompeii. (a) Aerial view of the city. Note that the upper £oors of most buildings are missing.(b) Front view of a wall pulled down in the house of the Chaste Lovers. The wall, transversal to the £ow direction, lays in theE1 unit. Note the darker, lithic-rich unit D below the wall. (c) Rear view of the same toppled wall. On the left, the still standingwall found in the fallout deposit; on the right, the upper part of the wall laying above unit D. (d) Section of the city walls closeto Capua Gate showing a high amount of destruction in the northern, volcanic vent-facing side. Flow direction from right toleft. Key: FU, fall units; PDCs U, pyroclastic density current units. The arrow links the base of the PDCs deposit with the pro-¢le of the destroyed wall.

VOLGEO 2630 21-7-03


port system) and settling progressively from abasal depositional system. During the transporta vertical £ux of grains (suspended-load fallout)is supplied from the transport system to theunderlying depositional system. Deposition iscontrolled by particle concentration, suspended-load fallout rate, the grain-size distribution andthe £ow power (Lowe, 1982, 1988; Druitt,1991). The presence of di¡use sedimentary struc-tures within the PDCs AD 79 deposit at Pompeiisuggests the dilute and expanded nature of thesepyroclastic currents. As a consequence, only thelowermost part of such currents has interactedwith the buildings at Pompeii.To explain type and distribution of the damage

mentioned above, the following model of the em-placement of the AD 79 PDCs at Pompeii is pro-posed. The ¢nding of toppled walls (and victims)

in unit E indicates a cause^e¡ect relationship be-tween the emplacement of the parental PDC andthe destruction of the buildings. This means thatthe thin ash layer C was emplaced without anysigni¢cant amount of destruction. Probably, itwas deposited by the distal and dilute part of aPDC. In fact, a decrease in concentration awayfrom the vent has been inferred from ¢eld featuresof several PDCs deposits (e.g. the 18 May 1980Mount St. Helens blast, Druitt, 1992; the Suwol-bong tu¡ ring in Korea, Sohn and Chough, 1989).The large-scale inhomogeneous distribution ofdamage suggests a non-uniform behaviour of thepyroclastic currents. As in the 1902 St. Pierreeruption surges (Fisher and Heiken, 1982), theAD 79 pyroclastic currents demolished mostlythe walls that happened to be perpendicular totheir £ow direction. The ¢nding of well preserved

Fig. 13. Sketch of a PDC £owing on the Pompeii urban structures. It is possible to distinguish an upper transport system thatsupplies, with an uniform rate, particles to a basal depositional system, variable in thickness. Two series of walls, transversal tothe £ow direction, are widely spaced. Near the ¢rst two obstacles (walls on the left), the depositional system is thin with a rela-tively low concentration of pyroclasts. From the ¢rst to the second series of obstacles, there is enough space to restore a thickbasal layer with relatively high concentration. This basal part has su⁄cient energy to deeply topple the transversal walls. Thepresence of the following closely spaced obstacles slow down the depositional system that losses part of its load; as a conse-quence, the thickness and concentration of the depositional system decreases progressively in correspondence of each wall.

VOLGEO 2630 21-7-03


brittle objects in closets located laterally to thechannel-shaped pro¢le of the demolished walls,inside the Polibius’ house, testi¢es that the de-structive impact of the PDCs is restricted alongwell de¢ned paths. Indeed, the areas outside thechannels represent places where PDCs show es-sentially depositional behaviour. The channellingof the basal part of the currents along the centralaxis of the buildings is probably an e¡ect of thebounding of the longitudinal walls. Furthermore,as in the case of the Polibius’ house, the walls wereprogressively less damaged down-current for eachsingle building; however, where an open space(10^20 m) occurs between two closely spaced(2^3 m) series of walls, the amount of demolitionbecame high again (Fig. 13). It is suggested thatthis trend could re£ect a temporary reduction ofkinetic energy within the depositional system dueto local loss of mass (sedimentation) and velocityafter a series of repeated impacts against thebuildings. The loss of kinetic energy reduces thecapacity of the PDCs to destroy the walls anderode the underlying pumice fall deposit. Thebasal depositional system could restore its physi-cal characteristics once every series of obstacleswas overridden thanks to the continuous supplyof particles from the upper high-energy transportsystem that did not su¡er any breaking action bythese urban obstacles. A new decrease of kineticenergy occurs wherever a new series of closelyspaced obstacles occurs transversal to the £ow di-rection. The depositional system is non-uniform interms of concentration and occurs as a series oflongitudinal rarefactions and condensations in re-sponse to the distance between successive ob-stacles (assuming a constant supply of particlesfrom the upper transport system). Consequently,we suggest that local and temporary £uctuationsof kinetic energy within the depositional systemcan be induced by the interaction between the ur-ban structures and the base of the PDCs.Recently, Valentine (1998) estimated the dy-

namic overpressure necessary to completely de-stroy the buildings of the nearby city of Hercula-neum by the PDCs of the AD 79 eruption at 35^70 kPa. The extensive damage su¡ered by thePompeii buildings is possibly related to an analo-gous PDC overpressure.

There is peculiar damage in the Polibius’ housethat allows us to re¢ne the proposed £ow model.We know both from the volcanic vent locationand the sedimentary structures ^ namely dunesand cross-strati¢cation ^ that the pyroclastic cur-rents £owed southwards. The location of thehinges inside the rear rooms of the Polibius’ housedemonstrates the knocking down of the doorstowards the north (contrary to the previouslydocumented north^south PDCs £ow direction).Laboratory experiments about the e¡ects of to-pography on propagation and sedimentation ofdensity currents con¢rm that the presence of anobstacle of su⁄cient amplitude and transversal tothe £ow direction will lead to a partial blocking ofthe current and the production of a wave whichpropagates upstream (Bursik and Woods, 2000).We suggest that the present evidence is consistentwith the production of a re£ected £ow against thesouthern transversal walls of the peristyle. Thisre£ected £ow moved across the peristyle towardsthe rear of the house that was sheltered by thedirect impact of the PDCs by the adjacent build-ings located to the north of the Polibius’ house. Itstruck the wall and knocked down the doors to-wards the interior.

8. Emplacement temperature of the pyroclasticproducts

Several lines of evidence rule out the possibilityof a high emplacement temperature for all of thevolcanic products covering Pompeii. In the ¢rstplace, the typical textural features of high-temper-ature deposits (Branney and Kokelaar, 1992;Freundt and Schmincke, 1995) are totally absentfrom the observed stratigraphic sections of theAD 79 eruption. Moreover, a large amount ofaccretionary lapilli are present in the upper partof the stratigraphic sequence (units F, H and L),testifying to a depositional temperature not in ex-cess of 100‡C (Schumacher and Schmincke, 1991).Other strong evidence is provided by the largenumber of fugitive bodies buried in the middleof unit E (Luongo et al., 2003): the temperatureof the previously accumulated products (of bothfall and PDC origin) would not have been so high

VOLGEO 2630 21-7-03


as to prevent the Pompeii inhabitants from at-tempting to escape the disaster. Further evidencecomes from studies carried out on the previouslymentioned (Section 5.4) deformed glass fragment,the present tensional state of which results fromrapid cooling (Verita' et al., 2001), thus ruling outthe presence of a very hot and slowly cooling en-veloping pyroclastic deposit. Initially, the glassprobably softened because of a local combustionin the cupboard. In the same way, the largeamount of carbonised wooden relics recoveredfrom the pumice lapilli are to be attributed tomineralisation rather than to combustion phe-nomena.

9. Chronology of the events: the e¡ects of theAD 79 eruption on Pompeii

A reconstruction of the timing of the destruc-tive events in the city has been attempted. In theearly afternoon of August 24, a pumice fallstarted burying the city of Pompeii. During this¢rst phase of the eruption several roof collapsesoccurred, evident by abundant debris and tilesfound in the lapilli fall deposit. A signi¢cant num-ber of victims has also been found in this deposit(38% of the total of Pompeii victims; Luongo etal., 2003). They probably died as a consequenceof the building’s collapse. The accumulation rateof the deposit in the outdoor areas of the city isestimated at 15 cm/h. In the zones of the buildingswhere material sloughed from roofs, the accumu-lation rate reached values as high as 25^30 cm/h.Within 6 h the roofs and part of the walls of thebuildings had collapsed under the pumice load.On the morning of August 25, many buildings

had been destroyed almost completely and onlysome edi¢ces were still standing. A remarkablethickness of pumice lapilli, 1^5 m, had ¢lled theimpluvia and the rooms the roofs of which hadcollapsed. Also, the peristyles and the alleys hadbeen ¢lled to these depths. The lapilli pumice falldeposit, generally 3 m thick, totally buried thelower part of the buildings, partly protectingthem from the impact of the later pyroclastic cur-rents. The ¢rst PDC £owed through the city de-positing the basal ash layer C and causing irrele-

vant damage. A discrete explosion produced a fallthat formed the lithic-rich layer D. A local epi-sode of reworking suggests a brief pause beforethe emplacement of the next PDC. It showed agreater destructive force, £attened most of the(especially transversal) walls in its north^southpath. This PDC buried the ruins under a fewmetres of coarse ash and pumice deposit (unitE). A ¢nal phreatomagmatic phase, punctuatedby three lithic fall episodes, emplaced the upperpart of the succession (F^L units).A more detailed scenario has been recon-

structed for the Polibius’ house. During the ¢rstphase of the eruption a great quantity of pumicelapilli fell on the building (Fig. 14a), producingthe collapse of the front part of the house (Fig.14b) in a few hours. Probably as a consequence ofthese events, the inhabitants of the Polibius’ housedecided to hide in the rear rooms [GG] and [HH],the roofs of which, probably steeper than those inthe front of the house, had not been damaged bythe falling material. The pyroclastic currents ar-rived from the north, travelling parallel to thelong sides of the building: the northernmostwall, east^west oriented, was little, if at all, dam-aged by these currents because of the protectionby the adjacent buildings. The pyroclastic currentsovertopped the rear part of the house. Theymoved into the garden and advanced towardsthe front of the house. We suggest that the PDCthat emplaced unit E eroded the underlying pum-ice fall deposit and totally destroyed the upper£oor and the ground £oor walls perpendicularto the £ow direction (Fig. 14c). This current waschanneled between the longitudinal walls focusingits destructive power along the axis of the chan-nel. Outside of the erosional channel, walls andobjects were better preserved. In the rear of thebuilding only the room [EE], the western roof ofwhich had already collapsed under the pumicelapilli (see Section 5.6.1), was invaded from aboveby the pyroclastic currents. The remaining rooms,the roofs of which had remained in place and the£oor of which had not been covered with the fallpumice, were invaded through the peristyle (Fig.14c). No escape was possible for the people whohad taken shelter there. The ash, mixed withpieces from the roofs, reached every corner of

VOLGEO 2630 21-7-03


the rooms. A very hard and compact layer formedunder the beds: the skeletons were found lying onit. In the end, the roofs of the rear rooms alsocollapsed, covering the PDCs deposit with a re-worked ash and pumice deposit

10. Risk

The present research allows us to draw someconclusions concerning the impact of explosivevolcanic eruptions onto urban environments.First, it is possible to state that, as far pumicefall is concerned, risk is strongly dependent on

the slope of the roofs. Flat and low-angle roofsare prone to collapse under the pumice load,whereas steeper roofs tend to drain laterally thefalling material, causing the local accumulation ofthicker deposits (up to 5 m in the case of the AD79 eruption at Pompeii). The potential danger ofthese deposits should be taken into account wellin advance, especially in the case of long lastingeruptions and/or high accumulation rates. Build-ings should be planned so that neither obstructionof the ways out nor overload of nearby structurescan occur. It is very important to point out thatthe roof and wall collapses at Pompeii during thepumice fall phase of the eruption caused 38% loss

Fig. 14. The destructive e¡ects of the di¡erent eruptive phases on the Polibius’ house. The section is drawn according to trace Iin Fig. 6; Mount Vesuvius is to the left of the building. (a) Fall products accumulate in the alleys, on the roofs, in the peristyleand the rooms with impluvium during the early hours of the eruption. (b) Roofs and attics of some front rooms collapse underthe pumice lapilli load. (c) Pyroclastic currents by-pass the rear rooms and destroy the east^west trending walls in the front partof the house; a re£ected £ow invades the rooms where the inhabitants had taken shelter.

VOLGEO 2630 21-7-03


of lives. From a broader point of view this meansthat, if roofs are not properly constructed, a rel-atively high level of damage can be associatedwith these kinds of eruptive events. In particular,as the roofs of the buildings are £at and horizon-tal in the modern urban areas around Mount Ve-suvius, they too will be easily overloaded and col-lapse. A second consideration applies to thepyroclastic currents. They had a destructive im-pact on the structures that happened to strikeperpendicular to their £ow direction, whereasthey little, if at all, a¡ected those that happenedto be parallel. A clear example of this phenome-non in the Polibius’ house was provided by thesurprisingly intact objects found in the closets lo-cated along the eastern wall of the peristyle (seeSection 5.3)

Acknowledgements

We are grateful to Professor Guzzo, superin-tendent at Pompeii for inviting the authors toparticipate in the investigation at the Polibius’house. We also thank Dr. A. Ciarallo and hercollaborators for their logistic help and their in-terest in our research. We are deeply grateful toLivio Ruvo for critically reviewing a previous ver-sion of this paper. The editorial expertise of B.Marsh and the helpful comments of two anony-mous referees also helped to improve the manu-script. We extend our thanks to Dave Lentz forhis ¢nal revision of the manuscript.

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VOLGEO 2630 21-7-03


impact of the ad 79 explosive eruption on pompeii, i. relations amongst the depositional mechanisms...

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