Formation of Sinkholes in Gypsum Rocks in Iran: Insight into Geological Characteristics and Mechanism

Abstract

The existence of highly soluble evaporites in the form of Zagros Fold-Thrust Belt, especially in the case of the Gachsaran Formation, creates a favorable environment for sinkhole formation in gypsum rocks in the southwestern region of Iran. The aim of the current paper is to study the controls on the formation of sinkholes in five selected areas (Changleva, Tang Sarakh, Dishmook, Maroon, and Jaber) using a combination of field investigation, morphometric analysis, and spatial analysis in GIS environment. The outcome of the research suggests that there is no single determining factor in sinkhole formation, but it is the result of lithological, structural, and hydrogeological factors. Gypsum dissolution becomes the leading process of void development in the subsurface; meanwhile, marl beds become the local factors controlling permeability differences and the heterogeneity of the process of karstification. Structural elements, including fractures, joints, and syncline axes, greatly affect groundwater flow patterns and determine the location and direction of the process of dissolution. Morphometric analysis indicates certain trends in the geometrical characteristics of sinkholes in different regions of investigation from circular shapes to elongate and shaft-like onesIn addition, low-relief surfaces aid in enhancing infiltration and encourage progressive dissolution, while high-relief and highly fractured surfaces contribute to local collapse. While the natural karstification process is the most dominant mechanism for the development of sinkholes, human activities such as irrigation and pumping increase the rate of sinkhole formation through increased water-rock interaction and alteration of hydraulic conditions. In general, the development of sinkholes in the area under study is a long process involving geological and hydrological processes, and not just surface processes. This paper provides a framework for evaluating sinkhole risk in evaporitic regions of the Zagros region.