The formation of epikarst and its role in vadose speleogenesis

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Publication Date

January 2000

Publication Title

Speleogenesis: Evolution of Karst Aquifers

Abstract

The epikarstic zone differs structurally from the underlying bulk rock mass, reflecting the higher degree of fissuring and diffuse karstification due to unloading, weathering, and dissolution processes that encompass this uppermost layer of exposed rocks. An initial distinction in the permeability between the epikarstic zone and the bulk rock mass below is caused largely by nondissolutional processes. Contrast in hydraulic conductivity allows some groundwater storage in the epikarstic zone and flow cocentration at its base. Effective vertical leakage paths from the epikarstic zone (major tectonic fissures) commonly need no speleogenic initiation, as they are wide enough to support undersaturated flow through them. Shafts fed by epikarstic recharge represent headwaters of a conduit drainage system developed in the deeper parts of a massif. A large majority of single shafts, several tens of meters deep (the most common feature among explored vertical caves), belong to this type of epikarst-fed shafts. The opening of these shafts to the surface through collapse and subsidence, with subsequent edge smoothing, is probably the main mechanism of doline formation in exposed karsts, rather than gradual preferential lowering of the surface. Therefore, focused karst landforms reflect, through specific mechanisms of epikarst morphogenesis, the permeability pattern of the upper part of the vadose zone.

Document Type

Article

Language

English

Identifier

SFS0073639_00001

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