Solution subsidence structures (dolines) in Malta : their physical development and human use

Abstract

Solution subsidence structures or dolines, as they are more commonly known in the international literature, are common karst landforms in the Maltese Islands. A significant number lie buried beneath metres of soil and sediment while others are mere remnants of much larger structures. Furthermore, some dolines are found in positive relief while a significant percentage exhibit clear surface evidence of their existence. The principal aim of this research study is to present a comprehensive study on the formation, evolution, distribution and land use of subsidence structures in the Maltese Islands. A total of 57 subsidence structures located on the main islands of Malta, Gozo and Comino have been inspected and photographed. The main outcome of this exercise was the production of a doline catalogue, which is presented in Appendix 2. In addition, two maps illustrating the distribution of dolines across the Maltese Islands have been produced and presented through the use of Google Earth. The most representative dolines were further investigated and discussed as case studies. A morphometric analysis, consisting of a number of geometric parameters, has been conducted by means of a hand-held GPS for a total of 11 dolines representing the case studies under investigation. The investigations revealed that the distribution of dolines and the location of faults are closely related to each other. A very high proportion of dolines have formed in the Upper Coralline Limestone, a rock formation with a high secondary porosity. Moreover, a nearest neighbour analysis revealed that subsidence structures in Malta are randomly distributed with a tendency towards clustering while the Gozitan structures are randomly distributed with no tendency towards clustering or regularity. The investigation also concluded that the majority of dolines in Malta should be referred to as buried dolines or collapse dolines.