Structural control on karst collapse sinkhole formation

Geophysical Research Abstracts Vol. 15, EGU2013-8197, 2013 EGU General Assembly 2013 © Author(s) 2013. CC Attribution 3.0 License. Structuralcontrolonkarstcollapsesinkholeformation Antonio Santo (1), Alessandra Ascione (2), Stefano Mazzoli (2), and Nicoletta Santangelo (2) (1) Dipartimento di Ingegneria Idraulica, Geotecnica e Ambientale, Università Federico II, Naples, Italy (santo@unina.it), (2) Dipartimento di Scienze della Terra, Università Federico II, Naples, Italy (alessandra.ascione@unina.it) Collapse sinkholes owing their formation to erosion and deformation phenomena caused by subsurface karstificationarewidespreadinthecarbonatemassifsofpeninsularItaly.Incontrastwithsolutiondolines,whicharedensely distributedonthesubplanartopsurfacesofthecarbonatemassifs,thecollapsesinkholes(hereinafterlabelledkarst collapse sinkholes) generally occur as isolated landforms and mostly affect the slopes and piedmont areas. In the latterinstances,thesinkholesalsoaffectalluvialfanconglomerates,orslopedebris,overlyingthecarbonaterocks. Weinvestigatedthekarstcollapsesinkholesofthesouthern-centralApenninesmountainbelt(Italy),whichisrepresentativeofayoungorogenicsystem,characterisedbyrecenttectonicactivityandstrongseismicity.Theaimofthe studyistheidentificationofthecausativefactorswhichcontroltheoccurrenceofsuchhazardousphenomena.The study was based on a regional scale analysis on sinkhole distribution in relation to the local geological-structural, geomorphological and hydrogeological contexts, and was paralleled with field analysis of some selected areas. The regional scale analysisindicates thatthe karstcollapse sinkholesare not the mere response tothe concurrence of the climatic and lithological conditions which commonly favour the development of karst processes, the occurrence of such landforms appearing strongly influenced by distinctive structural and hydrogeological conditions. In particular, a close relationship between the karst collapse sinkholes and the main extensional faults showing evidence of late Quaternary activity may be envisaged. This is inferred from the spatial distribution of the karst collapsesinkholes,whichisstrikinglyuneven,thesinkholesgenerallyoccurringinalignmentsfollowinglargelate Quaternary fault zones, or being clustered at the terminations of those faults. In addition, areas affected by the occurrence of groups of sinkholes, are also characterised by the presence of H2S and/or CO2 mineral springs, gas vents and of travertine deposits. Such co-presence points to interrelations linking dissolution phenomena, and carbonate precipitation, to the rise of aggressive fluids. In particular, this suggests enhanced deep-seated dissolution, and carbonate deposition at surface, in presence of ascending mineral waters. These evidences point to the important role played by extensional fault zones in the migration of deeply derived fluids, thus suggesting that active faults, in particular, represent preferential pathways for fluid rising and mixing with shallow groundwater. In addition, a focus on the relationships between karst collapse sinkholes and extensional fault zone properties has shown how the fault length and depth, and the dimension of the damage zone, influence the sinkhole formation and evolution.