DEVELOPMENT OF CRACKS ON THE FLOOR OF LUNAR LAVA TUBES

The presence of lava tubes on the Moon and other planetary bodies has been inferred from the observation of skylights. Lunar lava tubes have dimensions significantly larger than those observed on Earth, and are regarded as potentially valuable assets that could host long-term lunar bases. The aim of this project is to develop a way to deduce the location of lunar lava tubes from observable surface features and determine their internal characteristics, such as width, depth, and how much of the tube has undergone tensile or compressive failure to evaluate tube stability. An elastic Finite Element model of an idealized lava tube was developed, which adopts lunar gravity and material characteristics. Only gravitational loading of the tube by the weight of the rock above and surrounding it is considered at this point. Lava tube widths and depths are varied and some models were repeated assuming Earth’s gravity. The stresses on the rock produced in these models were analyzed to determine where tensile and compressive failure was expected to occur, both along the walls of the tube and at the surface, where they could be examined by geophysical techniques before exploration of the tube. In all models, the surface bows down over the tube, but an elastic bulge develops some distance away from the tube center. The distance from the center of the lava tube to the summit of the bulge is always 1.8 ± 0.2 times the distance from the center of the tube to the maximum surface stress. Therefore, if a surface bulge and an area of high stress on the surface, perhaps highlighted by cracks, is observed, this relationship could be used to locate the tube causing them. The extent of tensile failure on the surface depends approximately linearly on tube width; this could be useful for deducing the width of a concealed tube. All lunar models that have tensile failure on the tube floor show that it affects over 65% of the floor; in most cases, over 80% is affected. However, no failure is expected on the floor of a lava tube that has the smaller dimensions of those observed in terrestrial lava flows. The possibility of extensive fracture on lunar lava tubes, in contrast to terrestrial ones, may be important to consider with respect to space exploration and utilization of these tubes as long-term bases. The work was supported by the NASA SSERVI GEODES, grant #80NSSC19M0216.