FRACTURE MAPPING IN VALENTINE, HERCULES LEG, AND GOLDEN DOME CAVES, LAVA BEDS NATIONAL MONUMENT: TESTING THE POTENTIAL TO REMOTELY MAP LUNAR LAVA TUBES

Geophysical Exploration of the Dynamics and Evolution of the Solar System (GEODES) seeks to apply geological and geophysical measurements to characterize subsurface void spaces, due to the potential for habitation of their lunar counterparts. Lava tubes on the Moon may provide shelter for future explorers, but it is important to understand their long-term stability. During 2 field seasons in Lava Beds National Monument, the GEODES team characterized lava tubes by determining if fractures on the cave walls can be observed through visible and/or infrared (thermal) imagery, and whether fractures can be mapped from the imagery to a level needed to perform structural stability analyses.

We mapped 3 lava tubes with different morphologies: Valentine (V), Hercules Leg (HL), and Golden Dome (GD) caves. Fractures were mapped, measured, and photographed at multiple locations within each cave, starting with just inside the cave on the right wall. Subsequent measurement sites were ~30 m along the wall until the back of the cave was reached.

At each measurement site, horizontal 3 m fracture profiles were acquired by laying a measuring tape along the wall and noting the distance to each subsequent fracture. Three vertical 1 m fracture profiles centered on the horizontal line (~1 m apart) were also acquired. Visible and thermal images were acquired at each measurement site.

Visible imagery best detected mapped fractures where vein minerals were a different color than the surrounding host rock. Wet and/or large aperture fractures were apparent in visible imagery, but small fractures were not easy to identify. Visible imagery acquisition also required a significant amount of light aimed at the cave wall to capture data.

Thermal data highlighted temperature differences of fractures that were conducive and currently permeable, with air or water flowing through them, as these fractures were often colder than the surrounding rock. In V, this effect was most notable close to the cave entrance, but diminishing with depth into the lava tube. In HL the temperature differences were observable its entire length, while in GD no site showed a strong thermal signature. This is likely an effect of temperature homogenization, creating similar temperatures for the walls, air and water with depth.

This research was supported by NASA SSERVI project GEODES (80NSSC19- M0216; PI Dr. Nicholas Schmerr, Univ. Maryland).