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Enviroscan Ukrainian Institute of Speleology and Karstology

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Speleogenesis issues:

Original article

UIS KHS Commission
Karst breakdown mechanisms from observations in the gypsum caves of the Western Ukraine: Implications for subsidence hazard assessment

The term karst breakdown is employed in this paper to denote the totality of processes and phenomena of gravitational and/or hydrodynamic destruction of the ceiling of a karst cavity and of the overlying sediments. It refers not only to the existence of a surface subsidence (collapse) feature but, first of all, to "internal" (hidden in the subsurface) structures which precede a surface form.
This study reports and discusses the results of direct mapping and examination of breakdown structures in the gypsum karst of the Western Ukraine at the level of their origin, i.e. in caves. Accessibility of numerous laterally extensive maze cave systems in the region provided an excellent opportunity for such an approach and made it possible to examine the relationship of breakdown structures with particular morphogenetic and geologic features in caves and to reveal stages of breakdown development.
It is found that breakdowns initiate mainly at specific speleogenetically or geologically "weakened" localities that classify into few distinct types. The most of breakdowns potent to propagate through the overburden relate with the outlet cupolas/domepits that represent places where water had discharged out of a cave to the upper aquifer during the period of transverse artesian speleogenesis. Distribution of breakdown structures does not appreciably correlate with the size of master passages. Several distinct mechanisms of the breakdown development are revealed, most of them proceed in several stages. They are controlled by speleogenetic, geological and hydrogeological factors.
We show that speleogenetic approach is indispensable for understanding of breakdown pre-requisites and mechanisms and for eventual subsidence hazard assessment. The direct cave observations aimed to both, speleogenetic investigation and breakdown characterization on regional or site-specific levels should be employed wherever possible.