THE ROLE OF CONDENSATION CORROSION ON SPELEOGENESIS IN SEMI-ARID ENVIRONMENTS: A MORPHOLOGICAL AND METEOROLOGICAL INVESTIGATION IN THE IBERIAN CHAIN, SPAIN

Cave passage morphology can indicate types of speleogenesis (i.e. epigene and hypogene). However, late-stage condensation corrosion processes may confound such interpretation. Active corrosion has been identified in limestone caves across the Iberian Chain of northeastern Spain, making this region a useful analog for non-active corrosion sites. We studied the micrometeorology and morphology of Cueva del Muerto (CDM) and Cueva del Pastor (CDP). High resolution monitors measured temperature of cave air and rock walls to detect small differences in temperature within vertical profiles. Thermal stratification creates convection cells within passages and induces condensation corrosion in the upper portion of the passage. We also measured relative humidity, barometric pressure, and CO₂ concentrations. Three stations were deployed in CDM, and one in CDP. In both caves the temperatures for ceiling air, floor air, and rock wall were very finely stratified. The average difference in temperature from floor air to ceiling air was 0.112°C, and from ceiling air to rock wall temperature was 0.133°C (March 22 to June 20, 2016). Relative humidity was above 40% until mid-April, and from May-June was always above 80%. Barometric pressure increases from the entrance toward the back of the cave. Average barometric pressure at each station ranged from 851.6 to 868.9 mbar. CO₂ concentrations in March range from 300 to 2500 ppm, and in June from 600 to >3000 ppm, increasing towards the back of the cave. At locations where corrosion is extreme, the limestone ceiling of the passage has become soft and powdery. Distinct coralloid popcorn lines indicate the transition between corrosion and deposition. Radial cross sections measured with a penetrometer (4.4 N/cm²) determined the depth to which the limestone has been corroded as <1 mm to 7 cm, before abrupt transition to unaltered limestone. Data support the possibility that condensation corrosion is ongoing, at least seasonally, in these caves.