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| Titel |
Deep conduit flow in karst aquifers revisited |
| VerfasserIn |
Georg Kaufmann, Franci Gabrovšek, Douchko Romanov |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250087988
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| Publikation (Nr.) |
 EGU/EGU2014-2100.pdf |
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| Zusammenfassung |
| Caves formed in soluble rocks such as limestone, anhydrite, or gypsum are efficient drainage
pathes for water moving through the aquifer from the surface of the host rock towards a
resurgence. The formation of caves is controlled by the physical solution of the host rock by
water and by the chemical solution of the host rock by water enriched with carbon dioxide.
Caves as large underground voids are simply the end member of secondary porosity and
conductivity characterizing the aquifer.
Caves and their relation to a (paleo-)base level are found both close to a (former) water
table (water-table caves) and extending far below a (former) water table (bathy-phreatic
caves). An explanation for this different speleogenetic evolution is the structural control:
Fractures and bedding partings are preferentially enlarged around more prominent faults, thus
the fracture density in the host rock controls the speleogenetic evolution. This widely
accepted explanation can be extended by adding other controls, e.g. a hydraulic
control: As temperature generally increases with depth, density and viscosity of water
change, and particularly the reduction of viscosity due to the increase in temperature
enhances flow. This hypothesis was proposed by Worthington (Worthington, S.
R. H.: Depth of conduit flow in unconfined carbonate aquifers, Geology, 29 (4),
335–338, 2001) as a major controlling factor for the evolution of deep-bathyphreatic
caves.
We compare the efficiency of structural and hydraulic control on the evolution of a cave
passage by numerical means, adding a third control, the chemical control to address the
change in solubility of the circulating water with depth. Our results show that the increase in
flow through deep bathy-phreatic passages due to the decrease in viscosity is by far
outweighted by effects such as the decrease in fracture width with depth due to lithostatic
stress and the decrease in solubility with depth. Hence, the existence of deep bathy-phreatic
cave passages is more likely to be controlled by the structural effect of prominent faults. |
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