Temperature distribution in karst systems: the role of air and water fluxes

A better understanding of heat fluxes and temperature distribution in continental rocks is of great importance for many engineering aspects (tunnelling, mining, geothermal research,…). This paper aims at providing a conceptual model of temperature distribution in karst environments which display thermal “anomalies” when compared to other rocks. In temperate regions, water circulations are usually high enough to completely “drain out” the geothermal heat flux at the bottom of karst systems (phreatic zone). A theoretical approach based on temperature measurements carried out in deep caves and boreholes demonstrates however that air circulations can largely dominate water infiltrations in the karst vadose zone, which can be as thick as 2000 m. Consequently, temperature gradients within this zone are similar to the lapse rate of humid air (~0.5°C/100 m). Yet, this value depends on the regional climatic context and might present some significant variations.