CHARACTERIZING THE MORPHOLOGY OF TERRESTRIAL LAVA TUBES WITH LIDAR: ANALOGS FOR LUNAR PITS

Lava tube caves are drained out tunnels that formed within flow fields during volcanic eruptions. While exploration of lava tube caves may be limited to partial segments of a full tube system, the morphology and preserved flow textures within these sections still provide information about their formation. The challenge is producing a map or model that captures the full three-dimensional morphology of the lava tube. Two-dimensional maps provide relevant details about the shape, textures, and dimensions, but are also static and limited by scale. Lidar surveys produce detailed three-dimensional models that show the morphology of the tube at the meter-scale and texture details at the centimeter-scale. Point cloud models of lava tubes created from lidar surveys provide continuous x,y,z coordinates of all areas in the tube to analyze the changes in morphology, the spatial relationship with the surface terrain, and the distribution of flow textures and hazards. We conducted a survey of Lava River Cave in Flagstaff, AZ in June, 2019 and collected 77 scans (7 exterior, 70 interior) along the entire 1.25 km length of the lava tube. The final point cloud is ~3.25 billion points. The entrance is a shallow collapse pit and the ceiling of the tube near this entrance is ~14 m below the surface. There are no other skylights along the length of the tube. The floor of the tube decreases ~10 m from the distal (upflow) end of the tube segment to the tube floor near the entrance (downstream). The pillar, or section where the tube bifurcates and reconnects, is approximately 45 m long and 28 m wide.

On the Moon, mare pits (voids) could be connected to lava tube caves. If a tube is accessible, it is unclear what geologic features could be observed, discovered, or encountered. The exploration and characterization of terrestrial lava tube caves has strong implications for the exploration of mare pits as they give insight into the complex morphology, flow textures, and hazards that may be encountered on the lunar surface. Two types of mare pits have been observed: deep pits with apparent overhangs and shallow pits with sloped floors. Open pits hint at connection with a cave/tube, ideal for a lidar survey. Shallow pits could be linked to a tube, similar to Lava River Cave, but would require a surface investigation. We have discovered a third pit in the Marius Hills region. This shallow pit is 80 x 50 m wide and is located 8 km south of Galilaei M crater. We will discuss details of Lava River Cave, this new mare pit, and applications to exploring pits on the Moon with Lidar.