Three-dimensional stability analyses of lunar lava tubes: Assessing the possibility of reconstructing lunar pit geometry

Lunar pits are widely interpreted as collapse features above subsurface voids, most plausibly lava tubes, and are therefore of interest for both planetary science and future exploration. This study presents a three-dimensional numerical framework to investigate the surface geometry of roof collapse above irregular lava tube geometries. Irregular tube shapes are generated using random fields imposed on a cylindrical base tunnel, and collapse is assessed with an upper bound finite element limit analysis (FELA) formulation within Mohr–Coulomb model. A set of realizations is analyzed to quantify collapse pit geometry and its variability. For each retained realization, the surface outline of the collapse pit is approximated by an ellipse. This representation provides the principal axes used to quantify pit shape and orientation. The analyses focus on their ratio and the orientation of the fitted ellipse relative to the tube axis. Out of 588 realizations, 238 produced collapse pits suitable for statistical evaluation. The results indicate that collapse pits are typically elongated, with a mean proportions between major to minor axis of approximately 2.5, and that the major axis is generally closely aligned with the underlying tube direction, implying that pit orientation in orbital imagery may serve as a first order proxy for subsurface tube directions. Comparison with Lunar Reconnaissance Orbiter Camera (LROC) Pit Atlas measurements shows agreement in the collapse elongations but reveals systematic differences in distribution shape. Lower gravity multipliers are associated with reduced elongations, suggesting that future probabilistic assessments should emphasize the lower tail of the gravity-multiplier distribution. The internal friction angle strongly influences pit size, whereas fluctuation scales and roof thickness exhibit only minor statistical effects within the investigated ranges. Additionally, several realizations produce multiple pits within a single collapse event, forming pit-chain-like configurations consistent with orbital observations.