LIDAR SURVEYS OF LAVA TUBES IN LAVA BEDS NATIONAL MONUMENT

Lava tube caves provide unprecedented access to the shallow (meters to tens of meters) interiors of lava flows. Surveying tube geometry and morphology can illuminate lava flow thermal history and emplacement mechanics. Over two field seasons in Lava Beds National Monument, California, our team collected ultra-high-resolution (< 10 cm) topography of four lava tubes, Hercules Leg, Skull, Valentine and, Indian Well Caves, using a terrestrial laser scanner (TLS). Overall, more than 78 GB of point data (latitude, longitude, elevation) of the exterior ground surface and tube interiors were collected. For example, our point cloud for ~50 m of Valentine Cave contains 748 million points (interior: 478 million, exterior: 270 million) from 28 TLS scans. Data processing routines are used interactively to remove trees and bushes from the data to produce a “bare-earth” topographic model.

The tubes visited range in diameter from < 1 m to > 10 m, and from 1 m to < 20 m of overburden. The interior morphology of the tubes remains pristine (i.e., un-eroded) after more than 10,000 years. The TLS data illuminate original lava tube flow formations (e.g., lava-coils, pillars, benches, and ropes) and post-emplacement deformation features (e.g., fractures, lava-drips, molded ceilings, and drop-blocks). Furthermore, the data provide context for geochemical and geophysical observations made in conjunction with the TLS survey.

Lava tube morphology, observable in the TLS data, informs each tube’s emplacement history. Skull Cave is the largest (~20 m in diameter) requiring a comparatively high lava discharge rate and suggesting this cave formed by roofing over a lava channel. In contrast, Valentine, Hercules Leg, and Indian Well Caves are narrower, (1 to 4 m) and have many branches, some of which rejoin the “main passage”, suggesting they formed by developing an anastomosing network of conduits within the lava flow.