Characteristics and Genesis of Subsurface Features in Glaciokarst Terrains

Abstract

Glaciokarst terrains are rich not only in specific landforms, but in subsurface forms as well. Long, complex cave systems are widespread in glaciokarst terrains, and the deepest caves are almost all found in glaciokarsts. On the other hand, as for the volume of cave chambers and passage dimensions, glaciokarst caves are not among the largest ones. One of the most important questions about glaciokarst speleogenesis is whether subglacial cave development exists at all, and if so, how effective it is. Other important issues are the age of glaciokarst caves and the karst hydrology of glaciokarst terrains. Characteristic features of alpine caves are vadose shafts and (sub)horizontal passage levels. The two main variations of passage profiles are the tubular phreatic and the canyon-like vadose cross-sections, moreover, the combination of the previous two also exists, it is the so-called keyhole profile. Among small-scale cave features, paragenetic shapes and scallops are presented in this chapter. Characteristic glaciokarst cave sediments are coarse debris, which are mainly the results of extreme high discharges, fine-grained varved carbonates, which are deposited due to back-flooding conditions, and speleothems, which grow mostly during warm periods, but if some special conditions are satisfied, they may grow even below actually glacier-covered terrains due to the so-called “common-ion effect”. Further on, cryogenic cave calcites are also formed in glaciokarst caves, but their amount is insignificant. As for the karst hydrology, extreme fluctuations are characteristic to glaciokarsts, meaning both high seasonal changes and relatively high daily changes according to melt cycles. Using U-series and cosmogenic nuclide methodology to date speleothems and detrital cave sediments, it is now evident that the majority of glaciokarst caves are polygenetic in origin, surviving one or more glacial periods. Preglacial caves (i.e. caves evolving since at least the Pliocene) are common in the Alps. On the other hand, there are approved postglacial caves as well, which are related to drumlins or isostatic fissures. Finally, subglacial speleogenesis is also proved to be possible, though it has a low rate. Ice-contact cave development takes place when a connected aquifer is formed in the glacier ice and in the neighbouring karstic rock mass.