Lofthellir Lava Tube Ice Cave, Iceland: Subsurface Micro-Glaciers, Rockfalls, Drone Lidar 3D-Mapping, and Implications for the Exploration of Potential Ice-Rich Lava Tubes on the Moon and Mars

The Lofthellir lava tube, Iceland, contains massive ice formations accumulated from meteoric H2O. We report here on micro-glaciers and rockfalls, as well as the first 3D-mapping of a lava tube and ice-rich cave by drone-borne lidar. Implications for the exploration of potential ice-rich lava tubes on the Moon and Mars are examined. Introduction: Caves and pits have been identified on the Moon and Mars, many of which are likely lava tubes and their associated skylights, respectively. Candidate impact-melt lava tubes and skylights recently reported at high latitude on the Moon [1], and volcanic lava tubes and skylights identified at high altitude on Mars’ giant volcanoes [2], might offer access not only to unique sheltered subsurface environments, but also to potential repositories of subsurface volatiles, in particular H2O ice. Given this prospect on the Moon and Mars, understanding the occurrence (origin, distribution, evolution through time) of ice inside lava tubes on Earth is important. While analogies between the Moon or Mars and the Earth regarding ice in lava tubes are not expected to be straightforward, some processes and features associated with ice in such subsurface environments might nevertheless be shared, e.g., the potential role of gravity in cave-ice dynamics (independent of the origin of the ice), or the role of freeze-thaw cycling on cave stability. In this context, we carried out a field investigation of the occurrence and effects of ice inside a terrestrial lava tube, with focus on characterizing quantitatively the cave’s physical environment and its range of icerelated geologic features and processes. Field Site: We selected the Lofthellir Lava Tube Ice Cave in Iceland, a young (therefore presenting limited weathering degradation) lava cave known to contain a wide variety of massive ice structures in close to pristine condition [3, 4]. Lofthellir is located in the Lake Myvatn region of Iceland, near where Apollo astronaut field geology training took place (Fig. 1). The Lofthellir lava flow is only 3.5 kyr old. The skylight giving access to the cave was first spotted by a local pilot (and perhaps also formed or widened) only in summer 1989 [5] (Fig. 2). The cave and its entrance are on private property. Access is restricted and must be coordinated via authorized private field guides (Saga Travel or Geo Travel Iceland). Our field work in the cave was carried out on 10–11 Oct 2018. Figure 1. Location of Lofthellir Lava Tube, Iceland.