Abstract: Habitability: Subsurface environments may preserve records of habitability or biosignatures, with more stable environmental conditions compared to surface (e.g., smaller variations in temperature and humidity) and reduced exposure to radiation; Lava tubes are expected on Mars, and candidates are observed from orbit; Few detailed studies of microbial populations in terrestrial lava caves; Also contain a variety of secondary minerals; Microbial activity may play a role in mineral formation or b…