Geological evidences of Cyclical Climatic changes and catasthrophic events in the Neapolitan urbanised area

Franco Ortolani ⁽¹⁾; Silvana Pagliuca ⁽²⁾; Valerio Buonomo⁽¹⁾

(1) Dipartimento di Pianificazione e Scienza del Territorio, Università di Napoli Federico II, Napoli, Italy; fortolan@unina.it

(2) ISAFOM, CNR, via Cupa Patacca, Ercolano, Napoli, Italy; pagliuca@ispaim.na.cnr.it

Key words: urbanisation, georesources, geological risk, Southern Italy.

The physical environment of the Neapolitan Metropolitan Area is affected by several natural problems linked to the recent geological evolution of the area (figure 1).

Figure 1

Figure 2

Somma-Vesuvius and the mountains surrounding the Campanian floodplain are affected by an active erosion of incoherent terrains and soils by surface run-off.

Figure 3

Figure 4

Sites with slopes greater than 60 percent are subject to sudden, fast and extremely dangerous mud flows ( for example, Sarno, May 1998 and Cervinara, December 1999) (figure 1).

The geoarchaeological research pointed out that many urban areas have been affected by the same local geological problems during all the historical period (figures 1, 2, 3, 4, 5 and 6).

Figure 5

Local seismicity, concentrated within the area of the Somma-Vesuvius volcanic system is characterized by events that reached even the IX degree of MCS scale at the epicentres. Local seismicity is also connected to the Phlegrean Fields volcanic activity - with  maximum predictable events of  IX degree of MCS, at the epicentre - and bradyseismic activity, with a maximum of  VI-VII degrees MCS.

A particular geoenvironmental problem is represented by the bradyseismic movements that affected all the Neapolitan urbanized surface coastal area (figures 1); in fact the roman buildings are usually found some meters (figure 6) below sea level. The last bradyseismic uplift happened in the Phlaegrean Phields in the period eigtheen eighty three-eighty five affecting an area densely populated around Napoli and also the western part of Napoli. The urban area of Napoli, from Roman Period to the end of Middle Ages, was affected by three bradyseismic movements that lowered the roman soil of eight-ten meters maximum (figure 6).

Figure 6

The bradyseismic movements are correlatable with the cyclical climatic variations (figure 7). The soil uplift happened during the warm-arid period named “ Enhanced Roman Greenhouse Effect” and “Enhanced Crusades Greenhouse Effect”; the soil surface lowered during the cold-humid periods named “Dark Age Little Ice Age” and “Little Ice Age”. According to this ciclicity we think that in the near future the Phlaegrean Area will be affected by another soil uplift. The Buildings existing in the Phlaegrean Area are not structured to resist to the bradyseismic soil deformations characterized by anomalous expansion.

Original researches evidenced that not well known Intraplinian Vesuvian eruptions alimented a lot of debris flows at the base of the calcareous mountains surrounding the Campanian Plane (figure 2); in fact we found ten-fifteen meters of resedimented pyroclastic sediments and soils covering the roman anthropized surface (for example in Castellammare di Stabia, Sarno). The stratigraphic recostructions evidenced that all the ancient towns built in the alluvial plains areas where affected by contemporaneous catasthrophic flooding (figures 2 and 8). We recognised three regional flood period. The first happened between the sixth and forth century Before Christ and we named it “Archaic Little Ice Age”; the second happened between the sixth and eight century A. D. and is named “Dark Age Little Ice Age”; the third happened between the sixtheenth and eighteenth century A. D. and is named “Little Ice Age”.

Geo-environmental risk and degradation in the metropolitan area is confirmed by the following data (Fig. 8):                                        - uncontrolled water extraction from  the groundwater (about 400 million cum/year for irrigation,

- 200 million cum/year for drinking water,

- 100 million cum /year for industrial uses);

- discharge of effluent into the groundwaters amounting to about 10 million cum/year;

- discharge of effluent into water courses amounting to approximately 400 million cum/year;

- discharge of about 600 million cum/year of partially treated effluent along the coast;

-disposal of about 2 million tons/year of solid urban waste, of which only a part in managed landfills;

- disposal of about 1 million tons /year of special solid  waste, about 500,000 tons /year of toxic or noxious waste and about 3 million tons/year of demolition waste.

Many urban areas are affected by sinkholes risk due to the presence of many old hollows in the subsurface.

It is worth underlining the need to restore the groundwaters of the Campanian Plain which should be considered as a regional strategic resource.

Official guidelines need to be issued with regard to the volcanic risk connected with the fall of pyroclastic terrains on buildings in the Phlaegrean Fields and Vesuvian areas.

In particular, as far as the Phlaegrean area is concerned, the bradyseismic risk must be borne in mind; therefore, we propose and underline the need to introduce appropriate antibradyseismic standards so as to enable buildings to withstand unhomogeneous topographic surface deformations.

Figure 7

Figure 8