Sinkhole are ephemeral karst feature linked to karstifiable rocks. These phenomena are very common in the Carnian Alps (NE Italy) and represent a severe geo-hazard for locals and human facilities. Few papers regarding NE Italian sinkhole integrate geomorphological investigations and geo-hazard assessment. Zini et al. (2015) and Calligaris et al. (2015) recently recognized and classified tens of sinkholes proximate to Tagliamento River Valley analyzing their evolution with the contribution of geophysical and hydrogeological techniques. But already in 2009 Calligaris et al., proceeded to a preliminary reconnaissance and identification of these features based also on previous papers by Burelli et al. (2004), by Cucchi and Piano (2002) and Gortani back in 1965. Since then, only few very detailed investigations were realized on specific areas. At now, the knowledge has been developed after an extensive work done overall regional territory. The study, funded by the Geological Survey of the Friuli Venezia Giulia Region brought out that more than 30 municipalities (among the 221 that make up the Region) are affected by sinkholes. Through this extensive analysis, more than 600 phenomena were identified, georeferenced and classified according to Gutiérrez et al. (2014). One of the areas most affected by this geo-hazard is the Ovaro Village (Fig. 1). Ovaro is set on an alluvial fan were moraine deposits are also present, in a N-S oriented valley where the Degano River flows. In a territory of about 58 km² with an elevation between 456 and 2.076 m a.s.l., 90 subsiding areas were identified. The municipality, in the past had some geo-hazard problems linked to sinking features. This is not surprising seen that, in Entrampo, a small hamlet of Ovaro sited in its NW side, close to Degano River, is located an historical and still active gypsum quarry. The evaporitic bedrock is not well exposed in the area, but it is widely present in the subsurface. Geotechnical and geophysical investigations highlighted its presence at variable depths: from few meters below the surface, until 50 m. Several have been the drilled boreholes and some of them were investigated also using a camera that clearly gave the possibility to identify the presence of cavities in the bedrock. The number of identified voids allowed to understand that the karstification degree is particularly high explaining in this way the presence of a karst surface landscape. From a lithological point of view, the area is characterized by the presence of an evaporitic bedrock (Bellerophon Fm. – Permian in age) mantled by fan deposits mixed with moraine ones. The chalks are saccharoidal and whitish, microcrystalline, poorly cemented where the hypogean karstic features are present. A bedrock with the just described characteristics highlight its poor geotechnical properties, which favor the occurrence of collapse or sagging phenomena that caused and could cause new future instabilities to the existing infrastructures. Acknowledgements The research activities have been funded by the Regional Geological Survey. References Burelli, G., Cleva, S., Cucchi, F., Oberti di Valnera, S. (2004). Stato di evoluzione di sinkholes in alcune aree montane del Friuli Venezia Giulia. 1° Seminario "Stato dell'arte sullo studio dei fenomeni di sinkholes", APAT, Roma, 159-170. Calligaris, C., Devoto S., Zini, L., Cucchi F. (2015). Evaporite geo-hazard in the Sauris area (Friuli Venezia Giulia Region – Northeast Italy). 14th Sinkhole Conference, NCKRI Symposium, 5-9 October 2015, 465-470, ISBN 978-0-9910009-5-1. Calligaris, C., Zini, L., Cucchi, F., Stefanelli, S. (2009). Gypsum’s role in the Friuli Venezia Giulia Sinkholes. Proceedings of the 2°Seminario “I sinkholes: gli sprofondamenti catastrofici nell’ambiente naturale ed in quello antropizzato”, ISPRA. Roma, 213-221. Cucchi, F., Piano, C. (2002). Ipercarsismo superficiale e sepolto nelle evaporiti del Friuli-Venezia-Giulia. Proceedings of Le voragini catastrofiche, un nuovo problema per la Toscana. Edizioni Regione Toscana, Grosseto, 35-41. Gortani M. (1965). Le doline alluvionali. Natura e Montagna, 3, 120-128. Gutiérrez F., Parise M., De Waele J., Jourde H. (2014). A review on natural and human-induced geohazards and impacts in karst. Earth-Science Reviews, 138, 61-88. Venturini C. (2009). Note illustrative della Carta Geologica d’Italia in scala 1:50.000, Foglio 031 Ampezzo. Serv. Geol. D’It., pp. 232. Venturini C. (2001). Geological Map of the Carnic Alps, western sheet. 1:25.000 scale. SEdizioni del Museo Friulano di Storia Naturale, Pubblicazione no.48, 2006. Zini L., Calligaris C., Forte E., Petronio L., Zavagno E., Boccali C., Cucchi F. (2015). A multidisciplinary approach in sinkhole analysis: The Quinis village case study (NE-Italy). Engineering Geology, 197, 132-144.

EVAPORITE SINKHOLE INVESTIGATIONS IN THE OVARO VILLAGE (NE ITALY)

CALLIGARIS, CHIARA;DEVOTO, STEFANO;ZINI, Luca;CUCCHI, FRANCO
2016

Abstract

Sinkhole are ephemeral karst feature linked to karstifiable rocks. These phenomena are very common in the Carnian Alps (NE Italy) and represent a severe geo-hazard for locals and human facilities. Few papers regarding NE Italian sinkhole integrate geomorphological investigations and geo-hazard assessment. Zini et al. (2015) and Calligaris et al. (2015) recently recognized and classified tens of sinkholes proximate to Tagliamento River Valley analyzing their evolution with the contribution of geophysical and hydrogeological techniques. But already in 2009 Calligaris et al., proceeded to a preliminary reconnaissance and identification of these features based also on previous papers by Burelli et al. (2004), by Cucchi and Piano (2002) and Gortani back in 1965. Since then, only few very detailed investigations were realized on specific areas. At now, the knowledge has been developed after an extensive work done overall regional territory. The study, funded by the Geological Survey of the Friuli Venezia Giulia Region brought out that more than 30 municipalities (among the 221 that make up the Region) are affected by sinkholes. Through this extensive analysis, more than 600 phenomena were identified, georeferenced and classified according to Gutiérrez et al. (2014). One of the areas most affected by this geo-hazard is the Ovaro Village (Fig. 1). Ovaro is set on an alluvial fan were moraine deposits are also present, in a N-S oriented valley where the Degano River flows. In a territory of about 58 km² with an elevation between 456 and 2.076 m a.s.l., 90 subsiding areas were identified. The municipality, in the past had some geo-hazard problems linked to sinking features. This is not surprising seen that, in Entrampo, a small hamlet of Ovaro sited in its NW side, close to Degano River, is located an historical and still active gypsum quarry. The evaporitic bedrock is not well exposed in the area, but it is widely present in the subsurface. Geotechnical and geophysical investigations highlighted its presence at variable depths: from few meters below the surface, until 50 m. Several have been the drilled boreholes and some of them were investigated also using a camera that clearly gave the possibility to identify the presence of cavities in the bedrock. The number of identified voids allowed to understand that the karstification degree is particularly high explaining in this way the presence of a karst surface landscape. From a lithological point of view, the area is characterized by the presence of an evaporitic bedrock (Bellerophon Fm. – Permian in age) mantled by fan deposits mixed with moraine ones. The chalks are saccharoidal and whitish, microcrystalline, poorly cemented where the hypogean karstic features are present. A bedrock with the just described characteristics highlight its poor geotechnical properties, which favor the occurrence of collapse or sagging phenomena that caused and could cause new future instabilities to the existing infrastructures. Acknowledgements The research activities have been funded by the Regional Geological Survey. References Burelli, G., Cleva, S., Cucchi, F., Oberti di Valnera, S. (2004). Stato di evoluzione di sinkholes in alcune aree montane del Friuli Venezia Giulia. 1° Seminario "Stato dell'arte sullo studio dei fenomeni di sinkholes", APAT, Roma, 159-170. Calligaris, C., Devoto S., Zini, L., Cucchi F. (2015). Evaporite geo-hazard in the Sauris area (Friuli Venezia Giulia Region – Northeast Italy). 14th Sinkhole Conference, NCKRI Symposium, 5-9 October 2015, 465-470, ISBN 978-0-9910009-5-1. Calligaris, C., Zini, L., Cucchi, F., Stefanelli, S. (2009). Gypsum’s role in the Friuli Venezia Giulia Sinkholes. Proceedings of the 2°Seminario “I sinkholes: gli sprofondamenti catastrofici nell’ambiente naturale ed in quello antropizzato”, ISPRA. Roma, 213-221. Cucchi, F., Piano, C. (2002). Ipercarsismo superficiale e sepolto nelle evaporiti del Friuli-Venezia-Giulia. Proceedings of Le voragini catastrofiche, un nuovo problema per la Toscana. Edizioni Regione Toscana, Grosseto, 35-41. Gortani M. (1965). Le doline alluvionali. Natura e Montagna, 3, 120-128. Gutiérrez F., Parise M., De Waele J., Jourde H. (2014). A review on natural and human-induced geohazards and impacts in karst. Earth-Science Reviews, 138, 61-88. Venturini C. (2009). Note illustrative della Carta Geologica d’Italia in scala 1:50.000, Foglio 031 Ampezzo. Serv. Geol. D’It., pp. 232. Venturini C. (2001). Geological Map of the Carnic Alps, western sheet. 1:25.000 scale. SEdizioni del Museo Friulano di Storia Naturale, Pubblicazione no.48, 2006. Zini L., Calligaris C., Forte E., Petronio L., Zavagno E., Boccali C., Cucchi F. (2015). A multidisciplinary approach in sinkhole analysis: The Quinis village case study (NE-Italy). Engineering Geology, 197, 132-144.
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