ANALYSIS OF A LAVA TUBE WITH LIDAR ON MAUNA LOA VOLCANO, HAWAI‘I

We surveyed an unnamed, 200-750 year-old lava tube cave on the northern flank of Mauna Loa volcano, Hawai‘i using a ground-based lidar system to create a georeferenced 3-dimensional point cloud of the tube and surface. We used a Riegl Vz-400 terrestrial laser scanner (TLS) mounted with a Nikon camera to provide true color and a Trimble R8 Differential GPS to provide precise positioning for the surface scans. Reflectors were also placed every ~20 meters within the tube as control points for the interior scans. In 2016 we collected ~70 scans along the tube system. Here, we report on 34 lidar scans (13 surface, 21 interior) that cover the 180 m-long northern section of the lava tube cave. The complete point cloud for this section includes ~600 million points. Lidar provides precise positioning of the lava tube relative to the scanner, and post processing places those measurements in geographic reference. Measurements of the point cloud shows the tube width is typically between 3 to 5.5 m, with min-max ranges of 0.8 to 10.2 m. The height of the tube ranges from 2.3 to 6.0 m and the roof is 1.4 to 3.6 m thick. The average slope of the floor for this section of the tube is 5.7°. However, the steepest part of the tube floor drops 10 m in elevation over a distance of 36 m for a slope of 15.5°. From the surface, the position of the tube can be marked by five skylights within the pāhoehoe flows within the flow field. Flow textures at one skylight indicate that it was open during the eruption and lava overflowed during surges through the tube. Side tubes in the upper walls on the interior are consistent with pāhoehoe flows that drained off-axis of the main tube. The interior flow textures are well preserved and show multiple terraces that formed as lava adhered to the wall during flow at a consistent level. Lava stalactites and ropey pāhoehoe floor textures are also present throughout the tube. Several pits have been discovered on Mars that may lead to lava tube cave systems and are possible sites for future exploration missions.