Cave climate: Assessment of airflow and ventilation

Abstract

Study of cave climates is a neglected aspect of microclimatology. An understanding of the processes that control cave climate is required in the study of cave flora and fauna, thermodynamic conditions for karst processes underground, hydrogeologic features of speleothems as well as human use of caves for recreational and commercial purposes. An understanding of cave airflow is of central importance as the climate of a cave is a function of air exchange with the outside environment. The study site is the Glowworm Cave of New Zealand and is of particular interest because of its heavy visitor use and the presence of climate sensitive cave fauna on which the value of the cave as a tourist attraction depends.The study examines airflow using conventional methods together with experimental procedures using SF, and CC12Fz tracer gases. The results show that the rate and direction of airflow are a direct response to a thermally induced disequilibrium in air density between the cave and outside air. Both diurnal and seasonal patterns in the direction of airflow were identified. Reversal of airflow occurs when the cave to outside air density gradient is zero rather than when thermal conditions of the cave and external air are the same. Major and minor airflow routes through the cave were identified. The results of the gas tracer experiments allowed estimation of rates of air change in different parts of the cave and confirm the marked difference in ventilation that occurs within the cave. Information of this type is important because of the relationship between natural ventilation and C02 buildup. There is also the effect of ventilation on differences in climate within the cave as the thermal and moisture effects of outside air will not be as pronounced in parts of the cave where air change is limited.

Seasonal temperature variations controlling cave ventilation processes in Cueva Larga, Puerto Rico

“…Changes in pCO 2 production in the soil could be an addition to the observed seasonal pCO 2 pattern, but seem to be of minor importance compared to changes in cave ventilation at this tropical site. Similar conclusions have been made at numerous other sites ( De Freitas et al, 1982;Pflitsch & Piasecki, 2003;Spötl et al, 2005;Kowalczk & Froelich, 2010;Cowan et al, 2013;Gregorič et al, 2013). Mattey et al (2016) found that decay of organic matter washed down into the unsaturated zone appears to be a CO 2 source of similar importance, which is likely to be annually constant.…”

Large‐scale anomaly patterns associated to temperature variability inside Scarisoara Ice Cave

“…The large amount of perennial ice in the Scarisoara Cave is a direct consequence of the cave's peculiar climate, which in turn is controlled by location and size of the cave entrance, the volume of the underground void, as well as local climatic conditions (Racovita and Onac, 2000). Scarisoara is a descending cave with a single entrance located at its upper part and therefore, belongs to the group of caves with seasonal bidirectional ventilation (Racovita 1967;De Freitas et al, 1982). This means, the aerodynamic exchanges with the exterior are limited to cold seasons when the outside colder and denser air sinks and cools down the cave.…”

Studies of condensation/evaporation processes in the Glowworm Cave, New Zealand

“…C. R. de Freitas and A. Schmekal Airflow in the cave has been studied in detail by de Freitas et al (1982) and shown to be the key component of a cave's climate (de Freitas & Littlejohn, 1987). The speed and direction of flow is determined by the difference of mean density of the outside and inside air (de Freitas et al, 1982). Since air density is mainly a function of air temperature, the latter can be used as the main indicator of airflow (de Freitas et al, 1982).…”

“…The speed and direction of flow is determined by the difference of mean density of the outside and inside air (de Freitas et al, 1982). Since air density is mainly a function of air temperature, the latter can be used as the main indicator of airflow (de Freitas et al, 1982). When the outside air is cooler and thus denser than the cave air, the warmer cave air rises and flows towards and then through the Upper Entrance and replaced by cold air at the Lower Entrance.…”

“…When the outside air is cooler and thus denser than the cave air, the warmer cave air rises and flows towards and then through the Upper Entrance and replaced by cold air at the Lower Entrance. When cave air is cooler and denser than the air outside the cave, it flows down through the cave and out the Lower Entrance (de Freitas et al, 1982). In transitional times where the temperature gradient inside and outside the cave is small, there is little or no airflow.…”