Morphometric constraints on the formation of new terrestrial analogs for planetary pits

Abstract

The origin of geological depressions abounding on Mars and other planetary bodies remains poorly understood, partially due to the limited variability in the geological settings of existing terrestrial analogs. Here, we present a new terrestrial analog that is located at the northwestern margin of the Levantine volcanic field of Harrat Ash−Shaam along the Dead Sea Transform. The analog site consists of tens of geological depressions (locally named “juba”) that morphologically resemble Martian bowl-shaped pits and occur within a Pleistocene basaltic plateau that overlies Meso-Cenozoic carbonates. To constrain plausible formation mechanisms for the juba depressions, we carried out detailed field mapping and morphometric analyses using a 0.25 m/pixel digital terrain model (DTM) derived from airborne light detection and ranging (LiDAR) survey covering 34 km2 of the study area, and centimeter-scale, ground-based LiDAR scans of selected juba depressions. We show that variable magnitudes of slope asymmetry between north- and south-facing walls within the juba depressions, along with different degrees of sediment infilling, provide effective proxies for the relative geomorphic maturity of these landforms, and in turn indicate asynchronous formation of the juba depressions after the Pleistocene emplacement of the Harrat Ash−Shaam basalts in the study area. Our findings preclude formation of the juba depressions by phreatomagmatic explosions and instead point toward collapse into missing subsurface volume. In a broader context, we propose that the morphometric analyses developed herein to distinguish between plausible juba formation mechanisms in the Harrat Ash−Shaam volcanic field can be extended to better constrain the formation mechanisms of similar pit features on Mars and other planetary bodies.