Quantitative Morphometry of the Ape Cave Lava Tube: A Statistical Framework for Terrestrial Analogue Studies of Planetary Subsurface Voids

Abstract Recent discoveries suggest that intact lava tubes exist in the Moon and Mars, crucial for establishing long-term habitable areas to protect future lunar and Martian dwellers from surface risks. Considering planetary lava tubes as potential natural shelters requires understanding their internal complexity, which is challenging due to the lack of instruments capable of accessing their interior. However, terrestrial lava tubes currently provide the only available analogue for planetary lava tube morphometry, though the degree to which they represent their extraterrestrial counterparts remains to be established. This study considered Ape Cave in Washington, USA, as a terrestrial analogue and used high-resolution 3D models and statistical clustering techniques to examine its morphometry. The results revealed significant variations in the cross-sections widths (1.02–18.82 m) and heights (1.61–11.28 m). The circular compactness of the sections showed a diverse range of geometries ranging from highly irregular to nearly circular. Aspect ratio values indicated the presence of verticalized and laterally elongated geometries.