The surface texture of martian lava flows as inferred from their decimeter- And meter-scale roughness

Abstract

Extensive lava flows are found in the equatorial region of Mars, shaping the surface in a very distinct way. In radar images (at the decimeter scale), these flows are bright, with circular polarization ratios greater than one. This is a typical characteristic of extremely rough, blocky lava flows on Earth. Although the source of the extreme dm-scale roughness of Martian lava flows is unknown, their surface roughness can be constrained at the meter scale in an effort to infer their emplacement style. Here, we utilized high-resolution HiRISE images of Mars to construct digital terrain models of 35 lava flows, and measure their surface roughness parameters at a scale never before examined. Our results show that at the meter scale, Martian lava flows are smoother than blocky flows seen on Earth, and similar in roughness to terrestrial pahoehoe and rubbly flows, as well as young lunar lava flows. However, these latter flows are much smoother at the decimeter scale than Martian lava flows. The differences observed in the surface roughness of Martian lava flows compared to analog lava flows on Earth and the Moon might be the result of: (1) the differences in the emplacement style of the lava flows, and/or (2) the differences in post-emplacement modification processes on the surface of the lava flows.