Stalactite drip rate variations controlled by air pressure changes: an example of non‐linear infiltration processes in the ‘Cueva del Agua’ (Spain)

Abstract

Abstract:A study of drip water from a stalactite in the Cueva del Agua (Granada, southern Spain) over four hydrological years has enabled a detailed characterization of infiltration through the non-saturated zone of this cave. The most significant aspects are:(1) The drip water regime is not seasonal, but is linked instead to slow infiltration. Sudden changes in the drip water regime are detected, due to infiltration along the preferential flow paths and the draining of water of supersaturated water reserves from the microfissure and pore system. (2) The accumulation of excess rain in the unsaturated zone dislodges the reserve of supersaturated water from the matrix of microfissures and pores, giving rise to an average increase in drip intensity of 2Ð2 š 0Ð5 mm h 1 and 37 š 13 µS cm 1 in the electrical conductivity of the water. (3) Time-series analysis of the drip water demonstrates a lack of linearity over time of the drip rate, indicating a chaotic regime. (4) When the dripping is constant, barometric oscillation of the air is the principal factor that causes the lack of linearity in the drip flow. In this way, over an average of 2-3 days, a mean variation of the air pressure inside the cave of 10 š 3Ð7 mbar causes a mean oscillation in the drip rate of 0Ð5 š 0Ð2 mm h 1 . This increase in air pressure is translated as an increase in the relative thickness of the gaseous phase of the drip water at the cost of the aqueous phase, so reducing the drip intensity of the stalactite.

Contribution of artificial galleries to the knowledge of karstic system behaviour in addition to natural cavern data

“…These remarks are essential because the events, which are described above, were underlined before by Emblanch et al (1999) at the outlet of the Fontaine de Vaucluse system and supposed by Fernández-Cortés et al (2006) in the Cueva del Agua (Granada, southern �pain). Here we show clearly that this phenomenon exists already in the unsaturated zone.…”

Spatially dense drip hydrological monitoring and infiltration behaviour at the Wellington Caves, South East Australia

“…This is the nearest station to record sub-daily barometric pressure and should be a reflection of any pressure changes at the surface above the cave. A negative correlation between drip rate and pressure with no (or a low) lag, would be indicative of two-phase-flow previously observed in French and British caves (Genty & Deflandre, 1998;Baker & Brunsdon, 2003;Fernández-Cortés et al, 2007;Verheyden et al, 2008). This is a direct process, whereby expansion or compression of air bubbles in the water is driven by local changes in atmospheric pressure, and either promotes or suppresses dripping (Genty & Deflandre, 1998).…”

“…The extent to which these different flow routes are significant at specific cave sites has yet to be directly observed, as cave based monitoring programs that utilise automated continuous data logging are often restricted to monitoring a single drip (Genty & Deflandre, 1998;Fernández-Cortés et al, 2007) or a maximum of ~10 drips (Fuller et al, 2008;Arbel et al, 2010;Miorandi et al, 2010) (Table 1). Crucially, the study of cave drip waters over a significant area of a single system should be useful in understanding when and how infiltration of cave drip waters in a karst area occurs; producing a dataset of continuous observations at a sub-hourly temporal resolution that can be used to develop site specific conceptual models and calibrate numerical models of these systems.…”

Hydrogeochemical processes as environmental indicators in drip water: study of the Cueva del Agua (Southern Spain)

“…Mean oscillation of air pressure in the cave is 10.0 ± 3.7 mbar, and this leads to a variation in drip intensity of 0.5 ± 0.2 mm·h -1 (Fernandez-Cortes et al, 2007). An increase in air pressure within the cave causes a similar increase in pressure in the air held in the network of fissures and pores associated with the drip water.…”

“…Studies of frequently-measured or automaticallylogged discharges (Smart & Friederich, 1986;Baker et al, 1997, �enty & Deflandre, 1998Tooth & Fairchild, 2003;Baker & Brunsdon, 2003;Sondag et al, 2003;Fairchild et al, 2006, Fernandez-Cortes et al, 2007McDonald & Drysdale, 2007) illustrate a range of hydrological responses to infiltration events. An alternative focus of some studies has been the combined analysis of temporal variation of the discharge and geochemical changes in the drip water, using:…”