Cave airflow mechanism of a crevice-type cave: A case study from Czechia

Abstract

At present, crevice-type caves are investigated mainly by means of geomorphic and geophysical methods. Microclimatic research of this type of caves is underrepresented and is often limited to temperature and humidity measurement only. Yet, microclimatic research of such caves can significantly help in the management and conservation of caves, speleological exploration or analysis of speleothems. Being the first ever research of ventilation within a crevice-type cave, a complex analysis of cave ventilation was performed within the Velka Ondrasova Cave, a crevice-type cave in the Outer Western Carpathians, Czechia. Long-term temperature recording, airflow tracing within the cave, and a total of nine monitoring field sessions (conducted between February and April 2015, in August 2015, and March 2018) provided data on temperature and airflow inside and outside the cave, serving as a basis for an analysis of ventilation rates, airflow routes within the cave, instability of the cave airflow, and the general ventilation mechanism of the cave. Based on the data, the average cave airflow velocity 0.27-0.61 m.s(-1) corresponding to the ventilation rates 540-1,260 m(3).h(-1) (similar to 13,000-30,000 m(3)/day) was estimated as a rough value of the ventilation, given the complex morphology of the cave. The Helmholtz resonator appeared to be an unsuitable model for an explanation of the instability within the cave airflow velocity. A regression analysis of the cave airflow highlighted the temperature gradient as an important predictor explaining almost 80% of the analyzed cave airflow variability. However, statistical testing suggested the outdoor wind to be also a relevant driving force of the cave ventilation, accounting for the active cave airflow regime during summer.