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The airflow pattern can also be altered by snow and ice. In a passage with a V-shaped longitudinal profile, the airflow is triggered by instability which causes the feedback between the relaxation length and airflow velocity.

In passages with non-uniform outlines and/or cross-sections, the relaxation length may depend on the flow direction, resulting in different airflow velocities in cold and warm periods for the same absolute temperature difference between the massif and the external temperature. This determines the temperature and density contrast between the inside and outside air, and the resulting pressure difference, which drives the airflow. As the outside air enters the subsurface, it approaches thermal equilibrium with the rock mass along a characteristic relaxation length. In this work, I present and use a numerical model of a passage embedded and thermally coupled to a rock mass to study the relationship between the airflow pattern and passage geometry. Observations show that seasonal airflow patterns in caves also depend on the geometry of passages. The most common driver of airflow in caves is the density difference between the subsurface and the outside air, known as the chimney effect. Understanding the airflow patterns in caves is critical to understanding the properties of the subsurface atmosphere and the chemical interactions between air, water, and rock. Caves and their surrounding fracture systems in the vadose zone of karst regions host a unique atmospheric environment.

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