How do caves breathe: The airflow patterns in karst underground.

Area of Science:

• Geology
• Environmental Science
• Atmospheric Science

Background:

• Caves and karst fracture systems create unique subsurface atmospheres.
• Understanding cave airflow is crucial for subsurface atmospheric properties and air-water-rock chemical interactions.
• The chimney effect, driven by air density differences, is the primary driver of cave airflow.

Purpose of the Study:

• To investigate the relationship between cave airflow patterns and passage geometry.
• To analyze how thermal equilibrium and relaxation length influence airflow velocity.
• To explore the impact of non-uniform passage shapes and V-shaped profiles on airflow dynamics.

Main Methods:

• Development and application of a numerical model simulating airflow in a passage coupled to a rock mass.
• Analysis of thermal equilibrium and characteristic relaxation length of air entering the subsurface.
• Examination of airflow behavior in passages with varying outlines, cross-sections, and longitudinal profiles.

Main Results:

• Passage geometry, including non-uniform outlines and V-shaped profiles, significantly affects airflow velocity and direction.
• Relaxation length depends on flow direction in non-uniform passages, leading to different airflow velocities seasonally.
• Instability in V-shaped passages creates a feedback loop between relaxation length and airflow velocity.

Conclusions:

• Cave passage geometry is a critical factor modulating airflow, impacting subsurface atmospheric conditions.
• Thermal inertia and heat transfer in rock influence relaxation lengths and create hysteresis in airflow behavior.
• Snow and ice can further alter cave airflow patterns, highlighting the complexity of subsurface atmospheric dynamics.