SSS10 Proceedings 066 - University College London · SSS10Proceedings+of+the10th+International+SpaceSyntax+Symposium++ VCutini+&VDi+Pinto+ On+the+slopes+of+Vesuvius:+Configurationas+a+threadbetweenhazardandopportunity+

SSS10 Proceedings of the 10th International Space Syntax Symposium

V Cutini & V Di Pinto On the slopes of Vesuvius: Configuration as a thread between hazard and opportunity

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On the slopes of Vesuvius: Configuration as a thread between hazard and opportunity

Valerio Cutini University of Pisa [email protected] Valerio Di Pinto University of Naples Federico II [email protected]

Abstract

This paper focuses on the urban agglomeration that has gone growing up along the centuries on the western side of Vesuvius, a still active and fearsome volcano, few kilometres southeast from Naples. In view of the dimension of the agglomeration and of the spontaneous and unplanned way it has been growing, the purpose is to investigate on the actual role Vesuvius – as an element of both danger and richness – has gone assuming in the urban self-‐organization. This paper will analyse the grid configuration of the whole settlement, in order to discuss the way Mount Vesuvius has been interiorized (if it actually has been) in the spatial choices and behaviour of the local communities so as to benefit from its presence and to co-‐exist with its threat. Three major results are expected from the findings: to examine and verify the actual resilience of the whole agglomeration, so as to evaluate the extent to which the concern and alarm are actually justified; to analyse the configurational state of the system in order to pinpoint possible actions for risk mitigation; more in general, and aside from the case of the Vesuvius area, to evaluate how risk from natural hazard is spontaneously mitigated in self-‐organized urban spaces; and if self-‐organized urban structures, when exposed to natural hazards, really work better than we may think or fear.

Keywords

Hazard, grid configuration, resilience, self-‐organization.

“Above these places lies Mt. Vesuvius, which, save for its summit, has dwellings all round, on farm-‐lands that are absolutely beautiful. As for the summit, a considerable part of it is flat, but all of it is unfruitful, and looks ash-‐coloured, and it shows pore-‐like cavities in masses of rock that are soot-‐coloured on the surface, these masses of rock looking as though they had been eaten out by fire; and hence one might infer that in earlier times this district was on fire and had craters of fire, and then, because the fuel gave out, was quenched. Perhaps, too, this is the cause of the fruitfulness of the country all round the mountain (…) And the whole of the gulf is garnished, in part by the cities which I have just mentioned, and in part by the residences and plantations, which, since they intervene in unbroken succession, present the appearance of a single city.”

Strabo, Geography, book V, chapter 4 (early 1st century A.D.)



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“This is Vesuvius, until recently green with wine leaves where the celebrated grapes filled the wet vats. These mountains Bacchus preferred more than the hills of his native Nysa, this is where the satyrs performed their dances. Here was the city of Venus [Pompeii] that she preferred over Sparta, and the city that was named after the glory of Hercules [Herculaneum]. Now everything is abeyantly buried from flames and gloomy ash: even the gods would not have permitted such a destruction.”

M. Valerius Martialis, Epigrammata, book IV. ep. 44(A.D. 87)

1. Introduction

The slopes of Vesuvius, on the western side of the volcano, are home to one of the most problematic urban areas all over Europe, frequently mentioned and discussed with concern and serious alarm (among others, Barnes, 2011). More than one million people presently live in the direct shadow of Vesuvius, within a wide agglomeration that has gone growing spontaneously along the centuries, without (and against) any territorial plan or policy, under the threat of a still active and fearsome volcano: its last eruption dates back to 1944 but a forthcoming catastrophic event is presently feared and even expected, so that scares keep periodically coming up, evoking the dreadful memory of the ancient tragedy occurred in A.D. 79.

Mount Vesuvius has a long eruptive history, which has been continuing for over 400,000 years, periodically peaking in major eruptions alternated with moderate energy events according to a cycle of about 20 years. The last greatest eruptions were in 1631 (more than 7,000 victims), 1760, 1794, 1834, 1861, 1872, 1906 (the most violent event in the twentieth century) and 1944 (the last great event, spewing out more than 70 million cubic metres of lava). Such a regular and frequent occurrence is therefore easily expected to have deposited into the historical memory of the local communities a deep ancestral fear of the volcano as well as a full awareness of the deadly risks coming from it. Yet, as the settlements have recently gone spontaneously growing despite that hazard, it may be presumed that such fear and awareness could not but have somehow oriented the form and the structure of the settlement, in order to safeguard it and to enhance its resilience.

Nonetheless, it ought to be noticed that Mount Vesuvius is not only an undisputed source of danger for the million inhabitants of its slopes. The volcanic ash and lapilli erupted from the craters and spread around along the ages have strongly fertilized its slopes, making that land outstandingly fruitful and an ideal breeding ground for an amount of local crops, such as special local varieties of tomatoes, apples, apricots and grapes. Furthermore, exceptionally favourable microclimatic conditions make the western slope of Mount Vesuvius a highly desirable location for residence, which can also benefit from a unique view of the entire gulf, from Naples to Capri and Sorrento.

Summing all up, what makes this wide context one of the most dangerous areas of the world, under terrific, permanent and not eliminable threat, is just what also makes it one of the richest and most attractive agricultural lands all over Italy, source of wealth and employment as well as a strong element of cultural identity.

The acknowledged presence of volcanic risk suggested in 2001 to encompass a wide area around Vesuvius, called ‘red zone’, including the 18 municipalities where, in case of violent eruption, a complete destruction is predicted and ought to be expected. Around the red zone, an orange zone, a yellow zone and a green one were defined, including progressively lower risk areas. In 2013 the red zone was extended up to its present consistency, which includes 27 municipalities, around 350 sq.km, with a population over 1,100,000 inhabitants. For some time now, there is full awareness of the terrific risk looming over the whole area; since 1995 the Italian department of Civil Protection has developed a National Emergency Plan for the evacuation of all the red zone residents in case of eruption, providing to move out the refugees by different transport modes and predetermined routes, so as to distribute them in 18 Italian regions, from Piedmont to Sicily. In the present paper



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the attention will be focused on the most exposed portion of this red zone, the coastal strip lying between the western slopes of Vesuvius and the seaside and bounded on the north by the southern edge of Naples and on the south by the northern edge of the Sorrento peninsula, covering an area of about 120 sq.km (Fig. 1): 9 municipalities, including Pompeii and Herculaneum, and a population of 380,000 inhabitants (tab. 1).

Figure 1: The observed area, superimposed to a 3D view of the Vesuvian coast The whole area is completely urbanized, as a result of the rapid development of the various ancient nuclei in the second post-‐war period, so as to presently appear a unique wide conglomeration sprawled over the western slopes of Mount Vesuvius.

Municipality area (km2) Population density of population

(inhabitants/km2) Portici 4.52 60,218 13,322 Ercolano 19.64 56,738 2,889 Torre del Greco 30.66 90,608 2,955 Trecase 6.14 9,179 1,495 Bosco Trecase 7.49 10,638 1,420 Bosco Reale 11.20 27,618 2,466 Torre Annunziata 7.33 48,013 6,550 Pompei 12.41 25,751 2,075

Scafati 19 50.275 2,646 TOTAL 118.39 379.038 3,202

Table 1: Municipalities within the observed area The commonly discussed matter obviously concerns the way of clearing out the whole area, resettling its inhabitants on a safer urban place – hard task to achieve, for economic and social reasons –, or the management of an emergency evacuation plan – challenging too, due to the breadth of the area (a rough rectangle, 20 km long and 7 km wide), its administrative fragmentation and its population density (3,202 inhabitants/km2, with a peak of 13,322 in the municipality of Portici, among the highest in Europe).

Far from neglecting such aspects and overlooking the actual problems, this research will look elsewhere, focusing on the spatial configuration of the area. Since its particular geographic



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conditions, tightened between the crater and the seaside, have undoubtedly strongly influenced the urban structure and its development down the centuries, this paper aims at investigating the actual role Vesuvius – as an element of both danger and richness – has gone assuming in the urban self-‐organization. In other words, this paper will discuss if mount Vesuvius has been taken into account in the spatial choices and behaviour of the local communities so as to determine the development of urban spaces compatible with the volcano, in order to benefit from its presence and to co-‐exist with its permanent threat. The thesis is that the presence of the volcano and the effects it induces on the surrounding urban area are somehow internalized within the configurational properties of its grid and can therefore be investigated and made to emerge by means of space syntax techniques.

The area appears covered with a continuous urbanization, as a consequence of the demographic growth of the pre-‐existent urban nuclei; among them, the most important and densely populated centres are (running from north to south) Ercolano, Torre del Greco, Torre Annunziata and Pompei. The resulting conurbation currently occupies the whole area on the western side of Vesuvius with a low density urban structure, interstitial with respect to the more densely built areas of the ancient nuclei. The theme of its adjacency to the hazards and opportunities of mount Vesuvius appears therefore flanked by the theme of its recent development as a conurbation, overlapping and replacing the pre-‐existing cities. Space syntax will hence be applied to analyse both those issues, so as to answer the crucial question regarding the capability of this special conurbation, thanks to its spatial configuration, to deal with the hazards and opportunities mount Vesuvius actually provides.

In the observed case study, the grid configuration appears suitable to describe the way the Vesuvian conurbation fits the specific condition and the geographic context of its site, so as to exploit the territorial opportunities it provides and to cope with the hazards it presents. In other words, such issue concerns the way, if any, the local communities materialize the fear from natural hazards and the attraction towards territorial opportunities, developing and adapting their settlements in order to prevent themselves from the former and to take benefit from the latter; in other words, it concerns the way, if any, the fear from natural hazards and the attraction towards territorial opportunities are actually internalized within the structure of the settlement, so that they can be made to emerge by mean of space syntax techniques. Furthermore, aside from the case of the Vesuvius area, the same findings are expected to indicate if actually risk from natural hazard is spontaneously mitigated in self-‐organized urban spaces, and if self-‐organized urban structures, when exposed to natural hazards, really work better than we may think or fear.

2. Backgrounds

As it was shown above, two wide issues appear crisscrossing under the singular case of the Vesuvius area. On the one hand, setting aside the threatening presence of the volcano, this case evokes the general issue of the genesis of a conurbation from the development of several pre-‐existing nuclei, which have gone growing and mutually merging so as to form a radically different urban settlement, provided with a new and different inner geography. Such issue can be suitably investigated by space syntax techniques, so as to point out the transformation the configurational state of each single system undergoes, as it progressively grows, merges to the others and concurs in forming a greater global system. And it can be easily observed that the inner geography of the conurbation -‐ when deriving from the growth of cities of similar size – deprives its original nuclei of their own centrality, which is addressed towards the connection fabric between them. The configurational effects of the genesis of a conurbation are clearly exemplified by the case of the making of the Versilian conurbation, along the northern Tuscany seaside, developed in the twentieth century as a consequence of the growth of the three main nuclei of Viareggio, Marina di Pietrasanta and Forte dei Marmi. The image in figure 2 represents the configurational state of the Versilian system (represented by the distribution of global integration value) at three dates -‐ 1939, 1954 and 2004 -‐, so as to reproduce its diachronic dynamics.

The image above points out the radical change the inner geography of the settlements undergoes as they go merging: their integration core appears migrating from the respective original cores towards the long seafront street that represents their main mutual connection; this configurational state actually corresponds to the distribution of urban centrality, as it is represented by the density of



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movement and activities. In such geography, the original urban nuclei of Viareggio, Marina di Pietrasanta and Forte dei Marmi appear to remain the repository of a merely local centrality, confirmed by the distribution of radius 3 integration value.

Figure 2: The diachronic genesis of the Versilian conurbation. Distribution of global integration The second issue, specifically related to the observed case study, is the close proximity of this conurbation with an acknowledged and permanent source of great risk, what Vesuvius undoubtedly is. When it goes at discussing the behaviour of an urban settlement in front of a natural disaster like a volcanic eruption, we enter the wide -‐ and widely discussed -‐ theme of urban resilience. Several declinations of such theme have been so far provided, aimed at reproducing different features: resilience has been from time to time appraised and regarded as the possibility of the territorial organization to rescue e make safe the affected population (Gil and Steinbach, 2008; Muhareb, 2009; 2011), the capability of the urban settlement to retain the efficient working of its plants and infrastructures (Jha et al., 2013), the steadiness of its social wholeness and cohesiveness (Paton and Johnston, 2006; Pelling, 2003; Cutter et al., 2003), the ability of quickly recovering after a disaster (Carpenter, 2012) or the capability of an urban system, thanks to its own spatial features, to adsorb destructions and transformations without significantly changing its inner geography (Cutini, 2013), and so on. What significantly links all these issues (and several others not mentioned above) is the reference to some impending (natural or artificial) hazard that cannot be avoided as well as the purpose of adsorbing it and going ahead, hanging over it despite the destructions it may cause. On such issues, space syntax has already played its part, discussing the role of the grid configuration on vulnerability to disasters and suggested the use of configurational indices for a variety of purposes: in order to reproduce the level of resilience with reference to the seismic risk (Sari and Kubat, 2011); to point out the spatial factors that provide the capacity of rebounding after a disaster (Carpenter, 2012; Carpenter, 2013), adsorbing the impact of change on inhabitancy and cultural identity (Koch and Carranza, 2013), or spreading risk, creating buffers and facilitating reorganization (Marcus and Colding, 2014); to investigate on the spatial features that can assure the capability of sustaining local alterations of the grid with limited changes on its global behaviour, what was called network resilience (Cutini, 2013). Although all these notions could be usefully applied in any situation concerned with the threat of disasters, in the present paper the network resilience will be taken into account, as a suitable tool for evaluating the efficiency of the streets network and its performance in the immediate post-‐perturbation phase, also with reference to urban accessibility and evacuation.

As this notion appraises resilience as a matter of diffused richness in alternative paths from any origin to any destination, three main indices have been so far introduced and tested, and they will be applied in the observed case study.



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A first, basic parameter is the mean connectivity value of the grid, which roughly reproduces the density and variety of paths connecting each line to all the others of the axial map. Low values of connectivity are expected standing for the frequent presence of obliged paths, while on the contrary high mean values, in case of paths interruption, are likely to guarantee a dense presence of alternative paths. Its value varies from 2 to n, thus reproducing the capability of the urban system to absorb a material grid transformation without significantly modifying its relational state: in other words, its capability to adapt its movement pattern to different spatial layouts. The roughness of this index derives from the fact that it merely depends on the number of connections, but is not influenced by their spatial distribution.

A further index of network resilience takes into account the distribution of shortest paths: being resilient the systems that are provided with a widespread presence of shortest paths all over the grid and, on the contrary, vulnerable those that are characterized by their dense concentration through a small number of spatial elements. On such basis, an indicator of resilience was introduced (Cutini, 2013) as the ratio of the highest choice value and the maximum frequency a line could present, what would occur if it were located on all the shortest paths between any couple of the other lines. If we consider an axial map of n lines, it was shown that this index, to be called frequency index, is

v = choicemax / (n2/2 – 3/2 n + 1)

The frequency value varies from 0 to 1, increasing as the resilience of the system decreases. Should a line be located on all the shortest paths connecting all the couples of lines (v = 1), the system would result vulnerable to its highest degree, in that each of its paths will share (and depend on) that single line. The idea that urban resilience somehow depends on the capacity of the whole system to take and adsorb local perturbations suggested to introduce a further configurational parameter, reproducing the strength of the correlation between the distribution of integration values at different scales (local versus global). Since integration was proved suitable for reproducing the distribution of urban centrality at different values of radius, a narrow correspondence of global and local integration can be assumed as a clue of steadiness of the system: any perturbation will be expected not to upset the local distribution of accessibility, as strongly anchored to its global pattern. In other words, the R2 coefficient of the correlation radius 3 versus radius n integration (called synergy coefficient) appears suitable for indicating resilience or vulnerability. Such parameter and the two presented above, taken together, can hence be used as tangible indicators of the resilience of the whole system.

Figure 3: The analysed Vesuvian conurbation



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3. Grid configuration and resilience

The construction of the Vesuvian urban system, because of the unavailability of a reliable and updated numerical cartography, has been manually drawn exploiting the official national imagery (Fig. 3). The process has been made in GIS environment, working on the WMS service provided by the Italian national cartography portal (pcn.minambiente.it).

The resulting set of public spaces has been modelled into depthmapX software (Varoudis, 2012), to be analysed by a configurational approach. The same software was used to process the map by angular segment analysis, assuming Tulip analysis at 1024 bins, and metric and segment step, respectively, as analysis type and radius type.

The discussion of the results can exploit the space syntax capability to construe multi-‐scalarity in urban grids. At the global scale (fig 4), the distribution of configurational values shows that the integration core, that is the set of lines with higher values of integration, retraces the main axis road that crosses the whole urban system, while the integration values follow a decay trend as the distance increases. The distribution of choice value is similar, but characterized by a much more emphasised peak on the main road axis.

Figure 4: Distribution of global integration (above) and global choice (below) -‐ Colours vary from red (higher values) to blue (lower values) according to the depthmap standard.



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At a local scale, the distribution of radius 3 integration (Fig 5) clearly highlights the historical original nuclei, as well as their weld joint along the main road axis. The development process based on this mechanism of merging is better shown by the comparison of local choice distribution at different metric radii (Fig 6).

Figure 5: Distribution of local integration -‐ topological radius R3 (depthmap std. colour ramp)

Figure 6: Distribution of local choice at different metric radii (depthmap std. colour ramp)

Summing up, the analysis of the urban grid shows how dependent the whole system is on a set of few lines; and such result can only be strongly related to the conurbation genesis process, that is the welding of standalone urban nuclei along a main road axis crossing the whole area.



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In order to evaluate the syntactic resilience of the whole system, the indexes above have been calculated with reference to the entire conurbation, without any fragmentation into sub-‐elements. Each computation has been carried out basing on the result of angular segment analysis, assuming a topological radius 3. The numerical output is reported below (tab. 2).

Mean Connectivity Synergy Frequency Coefficient

4.62 0.169 0.396

Angular Segment Analysis – T1024 – Topological Radius

Table 2: Resilience Indexes calculated on the Vesuvian conurbation system Discussing the meaning of those results without any endogenous basis for comparison is a difficult issue. None of those indexes, in fact, was so far clearly classified in literature and, moreover, they are probably still underdeveloped (Conroy Dalton, 2010). However, referring to other available findings, mean connectivity and frequency (Cutini, 2013) values appear perfectly consistent with what the distribution of choice and integration, both at global and local scale, let us foresee: a poorly connected network (as shown by a low value of mean connectivity), with a high concentration of geodesic paths. Moreover, the poor value of synergy coefficient clearly means a weak correspondence between local and global scale, thus standing -‐ as discussed above -‐ for poor resilience.

Going deeper into the problem of the resilience of the Vesuvian conurbation, the relationship between resilience and risk needs to be pointed out, requiring some further consideration on the notion of resilience, which in urban studies, as hinted above, is not unequivocally defined (Esposito and Di Pinto, 2014). In order to clear out any ambiguity, in general we should assume that there is not a ‘resilience’ if not related to a well defined urban phenomenon to which a “perturbation” of the system is to be referred to; what involves that, in general terms, there are so many ‘resiliencies’ as urban phenomena. Despite the configuration of the urban grid is not a phenomenon in itself, but the common language of the space that influences urban phenomena (Hillier, 1999), yet it is movement what shapes this influence, as the very interface between the grid configuration and the phenomena along its paths; what was strongly pointed out defining the grid as a mechanism for ‘maximising the randomness of encounter through spatial proximity and movement’ and thus cities as ‘movement economies’ (Hillier, 1996). It is therefore movement what also substantiates the notion of network resilience, mentioned above and appraised as an intrinsic property of the urban grid. Such a meaning can here be enriched by the reference to the presence of an actual risk. In general terms, the risk is constituted by two components: the magnitude of a potential loss, and the probability that the loss will occur. Strategies for risk management may therefore point to reduce the loss or to lower the probability that it will occur. If attention is focused on the loss, it can be understood as the result of the overlap between a perturbation induced by an exogenous factor and the endogenous reorganization of a system. Configuration analysis is highly suitable for looking into both those aspects with an integrated approach, through the evaluation of the indexes of permeability before and after the event. In addition, the configurational analysis can even do more and better: it can assess the potential of a system to reorganize after a change, regardless of the nature and location of the perturbation. Moreover, thanks to this feature, it is also possible to assess the resilience of any urban phenomena dependent on space configuration: what actually completes and extend the notion of network resilience. Having taken that into account, when it comes to the object of the present study, a deeper and more area-‐oriented analysis can hence be performed. In particular, a heavy spatial impedance appears to affect movement towards the boundary of the conurbation: what is likely to involve dramatic problems if a catastrophic event should occur, thus suggesting discussion on possible risk mitigation.



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4. Configuration and risk mitigation

In order to evaluate the resilience as an endogenous property of the urban network, the configurational indexes introduced above are to be interpreted. The mean connectivity value, roughly reproducing the density and variety of paths within the grid, can be read as an indicator of connection redundancy to/from each point. In case of perturbation, the higher the mean connectivity, the smaller the isolation of any point in the network is likely to be. The synergy coefficient, measuring how much the local street system is a reliable predictor of global configuration (Conroy Dalton, 2010), actually expresses the average impedance that local pattern represents when moving from any point to the main elements of the network, and generally from the edge towards the centre. In case of perturbation, the greater the synergy, the lower the impedance (in terms of topological steps) to reach the main structure of the system will be expected. The frequency coefficient (Cutini, 2013) actually concerns movement: it expresses the degree of concentration of shortest paths within the grid. In case of an event, the higher its value, the smaller the probability of being near a high choice line will result; or, in other terms, more difficult moving toward the grid boundary will be. Moreover, the interruption of few high choice lines could easily upset the movement pattern all over the grid, or even undermine and jeopardize the whole system, making it not entirely connected. In order to capitalize on the use of those indexes, it is worth introducing endogenous references. Besides the present grid consistency of the settlement, two additional scenarios have been generated and analysed. A diachronic scenario is aimed at understanding how the dynamics of the settlements has gone influencing the change in resilience. The second, referred to the current situation, is then aimed at understanding if the infrastructures for non-‐local movement do actually play a role with respect to the system resilience. The first scenario (SC_1957) describes the system at 1957. The second (SC_2015_MWY) describes the system at 2015, but supplements it with the motorway A3 that crosses it (Fig. 7).

Figure 7: Segment maps of SC_2015_MWY (on the left) and SC_1957 (on the right)

The resilience coefficients were calculated with reference to the three scenarios, and their comparison (tab. 3) highlights the features of the settlement dynamics, characterized by the transition from a linear system of urban nuclei to an uninterrupted coastal conurbation. The actual increase in synergy values between 1957 (SC_1957) and 2015 (SC_2015; SC_2015_MWY) appears a consequence of the transition from a series of related parts (high synergy within each nucleus and low synergy of their whole set) to a uniform urban system (higher synergy value within the whole settlement). On the other hand, the significant decrease of mean connectivity expresses in configurational terms the decrease in density of the urban system as a whole. This is due to the way the new spaces have been arranged, which allows defining the development as a form of urban sprawl. The outstanding increase of the frequency value clearly reproduces the strong concentration of shortest paths towards a small number of highly crowded lines, hence highlighting the presence of a relevant transport problem and, what mainly concerns our issue, a significant decrease in network resilience. As a matter of fact, it means that in the last 60 years of uncontrolled urbanization the



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Vesuvian system appears much more vulnerable, in that it results more exposed to the isolation of some of its parts and may even collapse under a disaster.

Table 3: The comparison of resilience indexes among the three urban scenarios With regard to the motorway, the comparison between SC_2015 and SC_2015_MWY expresses a substantial equivalence. The only parameter that appears significantly modified is the frequency coefficient, decreasing and hence showing a more uniform distribution of global choice. Such result can be interpreted as the likely effect of the presence of the motorway, which supplements the urban streets and improperly reinforces their role of connection all over the area, thus actually enhancing the resilience of the system. It has to be noted that such a role of supplement and support highly complicates the ordinary working of the A3, the backbone of the Italian road network as well as the most used and crowded national motorway, which is actually subject to continuous problems of traffic congestion. Motorway A3 here appears assuming a promiscuous function, as significant local movement comes on top of the heavy road traffic running down the Italian peninsula.

The scenario SC_2015_MWY was then analysed by Principal Component Analysis (PCA), as described elsewhere (Esposito and Di Pinto, 2015), which provided a graph of two significant principal components. On such graph each line of the segment map is represented by a single point, whose position results from the combination of 10 configurational variables, at a global and local scale. The grouping of those points allows a hierarchical cluster analysis, which provides three homogeneous groups, representing aspects of the working of the Vesuvius area in the selected scenario. In particular, one of these groups mainly depends (in statistical terms) on local configurational variables, thus describing the structure of urban phenomena at a local scale (for example, movement in residential areas). With regard to the findings of our case study, the lines representing the Motorway A3 belong to the group of lines that are critical for the local functioning of the urban system (fig. 8); what is actually confirmed by the distribution of traffic flows between the motorway nodes within the whole area.



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Figure 8: Principal Component Analysis of SC_2015_MWY’s segment map: the cluster of lines that play a crucial role in the global (red lines) and local behaviour (green lines) of the system

5. Conclusions

In conclusion, three main issues, hereinafter roughly summarised, seem to arise from the results above. First, the spontaneous and uncontrolled development of the Vesuvian area has gone providing slightly positive effects on the spatial possibility of coming out of the conurbation, as a result of the moderate increase of escape routes from the area. Moreover, the lowering of the density of the system, due to the spatial organization of new development areas, widespread all over the conurbation, is likely to expose more people at risk of being isolated and cut off in the event of a catastrophic eruption. Furthermore, the A3 motorway actually appears to play a decisive role supporting the local transport system in the area, whether in the case of catastrophic event or in everyday ordinary behaviour; even tough, as stressed above, such role involves serious traffic problems.

We can conclude from this that the development of the last decades has significantly reduced the resilience of the whole area, thus increasing its vulnerability to possible eruptions. The expectation that the fear of the volcano could be somehow interiorized in the behavioural choices of the local communities -‐ so as to influence and orient the development of their settlement -‐ remains actually disappointed: in such influence the attractiveness of the locational qualities of Mount Vesuvius seems to have played a far greater role than the recollection of past eruptions, which evidently have gone fading from the historic memory; just as happened at the times of Strabo. It is to be hoped that the poor resilience here verified won’t be actually put to the test in the foreseeable future.



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