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Stefania Nisio, APAT- Geological Survey of Italy (Italy)
Vitale Valerio, APAT- Geological Survey of Italy (Italy)
Giarcarlo Ciotoli, La Sapienza University of Rome (Italy)
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On the basis of the recent researches catastrophic subsidences occur in Abruzzi region (Italy) plain areas and are primarily concentrated in intermountain basins or alluvial plains in the immediate vicinity of carbonate ridges. Sinkholes verified in complex geological-structural and hydrogeological scenarios and some of their can be originated by piping phenomena. Piping sinkholes could be triggered by various natural causes (seismicity, drought, flood, pumping of water and so on). In many cases the presence of active faults has been recognized. These faults can act as migration pathways for deep aggressive acidic fluids (enriched in CO2 and H2S) able to dissolve the carbonate matrix decreasing the mechanical characteristics of shallow soil.
In the Abruzzi region some sub circular water-filled ponds that could be ascribed to piping sinkholes have been identified.
In this work the first results of sinkholes census in the Abruzzi region, as well as a theory about the of the sinkhole prone areas is presented. Furtheromore, a first approach to a susceptibility study is presented consideraing numerous parameters, i.e. depth of the substratum, geotechnical characteristics of the sedimentary cover, seismicity, presence of active faults, etc. Results regarding some examples in the Aterno River valley, Sulmona plain, and Fucino plain are discussed.
The Aterno River valley, shows a general Apennine trend (NW-SE). Five sinkhole prone areas have been recognised along the Apennine trending section within a distance of tens of kilometres (a total of 35 sinkholes): in the high Aterno valley near the village of Pizzoli-S. Vittorino; in the medium Aterno valley near the villages of S.Gregorio and Civita , Demetrio ne Vestini and S. Pio delle Camere; in the low Aterno Valley (Sulmona plain) in the Raiano-Prezze area. The diameters of these sinkholes range from 30 to 40 meters in the first area with an enlargement trend in the central area of the river valley (up to several hundred of metres). The Fucino plain is a rhomboidal intermountain tectonic depression; during the Quaternary, the basin was deprived of a natural outlet and thus hosted a wide lake that collected a thick sequence of Pleistocene and Holocene silty lacustrine deposits interbedded with coarse alluvial fan deposits at its borders. Data from subsurface investigations, as well as geophysical surveys demonstrate that a network of capable faults affects the very recent deposits of the basin floor. A total of 30 sub-circular shaped cavities with diameters ranging from 5 to 30 m and few meters depth have been identified in the plain. These cavities occur mainly in the north-western sector of the Fucino plain with an E-W trend. In this area, high soil gas concentrations (CO2, He and Rn) of deep origin have been measured indicating fluid upwelling from a deep reservoir along buried tectonic discontinuities.
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