Morphometric analysis of sinkholes in a karst coastal area of southern Apulia (Italy)

Abstract

Salento, the southern portion of Apulia region (SE Italy), is a narrow and elongated peninsula in carbonate rocks, with prevailing low coastlines, locally interrupted by high rock cliffs. The long stretches of low coasts are marked by typical karst landforms consisting of collapse sinkholes. As observed in many other karst coastal settings worldwide, development of sinkholes may be particularly severe along the coasts, where both natural and anthropogenic processes contribute to accelerate the dissolution of carbonate rocks and subsidence processes, even influencing the coastline evolution. Following a previous study, where the main features of sinkholes at Torre Castiglione (Taranto province) were investigated and described, and a preliminary susceptibility map produced, at the light of updated data and elaborations in the present paper we perform a detailed morphometric analysis on the sample of identified sinkholes. The main morphometric parameters generally used for sinkhole characterization have been considered in this study: shape of the sinkhole, azimuth and length of maximum and minimum axes, depth, elongation ratio, and distance from the shorelines. Each of them is described, both as individual parameter and in conjunction with the others, in the attempt to identify the main factors controlling development of sinkholes in the area, and their evolution as well. With regard to this latter aspect, beside simple morphometry of the sample of sinkholes at Torre Castiglione, we also focused our attention on the likely relationships existing between distribution and shape of the sinkholes and the tectonic discontinuities. To investigate the matter, a three-stage analysis has been carried out in this study by means of: field measurements of the fractures bounding the sinkholes, field measurement of the long axes azimuth of the elongated sinkholes, comparison of the previously described sets with the strikes of the main regional geological structures. The obtained results show, in addition to the coincidence of the main regional discontinuity systems with the major axis of elongated sinkholes, a clear control exerted by development and evolution of the sinkholes on the formation of coastal inlets and bays. Eventually, the approach here presented may be applied in other karst coastal sinkhole-prone areas, to gain new knowledge on the genesis and evolution of coastal sinkholes, and to properly evaluate the hazard they pose to the anthropogenic environment. © 2013 Springer-Verlag Berlin Heidelberg

Part 1: Contemporary Challenges and Current Solutions in Sinkhole Occurrence and Mitigation

“…solubility and strength [14] Landscape evolution along coasts, e.g. inlets and bays [15] Known to occur more in evaporite than carbonate karsts due to higher solubility and lower strength [6] Seismic events/earthquakes [16] Groundwater flow-affected by rainfall (recharge) [17] Human Climatic change [6] Changes to drainage patterns-sinkhole frequency increases near drainages, fault, etc. [18] Subsurface drainage also needs consideration-e.g.…”

“…Eastern part of Saudi Arabia-land subsidence problems [29] Eastern Dead Sea shoreline in Jordan-old water channels and water table effects, plus active tectonism [30] Apulia in southern Italy-coastal plains [15,31] Plains in carbonatic ridges of bedrock outcrops in the Apennines [20] Rock type: evaporites Britain-evaporite karst causing subsidence and building damage [32] Hamburg, Germany-salt diaper; seismically affected [16,33] Rock type: calcareous Co. Durham, UK-gypsum dissolution below town of Darlington [34] NE Spain-evaporite dissolution (gypsum, halite, Na-sulphates) under alluvial deposits; groundwater flow accelerates dissolution [17] In turn, sinkholes affect human structures. For example, the Madrid-Barcelona high-speed railway is affected by human-induced sinkholes; land usage in Hamburg, Germany; and causing damage to the built environment, as with mining geohazards in Reading [35][36][37].…”

Lidar Processing for Defining Sinkhole Characteristics under Dense Forest Cover: A Case Study in the Dinaric Mountains

“…However, in morphometric analysis of sinkholes, elongation ratio Re is the ratio between the major and the minor axis (Gutiérrez-Santolalla et al, 2005;Kemmerly, 1976;Williams, 1972) . According to (Basso et al, 2013), we classify sinkholes into 4 groups regarding the elongation ratio Re: (i) circular and subcircular (Re ≤ 1.21), (ii) elliptical (1.21 < Re ≤ 1.65), (iii) subelliptical (1.65 < Re ≤ 1.8) and (iv) elongated (Re > 1.8). There is no common method of calculation of circularity index, (see (Denizman, 2003;Doctor and Young, 2013).…”

“…Sinkholes were the first karst landforms that were the subject of morphometric analysis (Basso et al, 2013). Early studies, e.g., (Lavalle, 1967;Williams, 1972Williams, , 1971, showed a great variety of morphometric parameters existed among sinkholes, depending mainly upon the different karst development and genesis of sinkholes.…”

“…In this case we refer to DTMs in the sense of height information of the bare ground plane as in (Newby, 2012). It is quite difficult to have high resolution and significant accuracy in forested karst areas using photogrammetry (Podobnikar et al, 2008); costly and time-consuming fieldwork can provide the necessary data for morphometric studies of karst landforms (Basso et al, 2013).…”