Thermokarst and Related Landforms in Western Utopia Planitia, Mars: Implications for Near-Surface Excess Ice

Introduction: Using high resolution Mars Orbiter Camera and Thermal Emission Imaging System images, we have identified pits that occur at the junction of polygons (referred to as polygon pits) (fig. 1) in western Utopia Planitia (UP), Mars (241.71° W, 305.27° W and 39.46° N, 57.57° N). We argue that the polygon pits are geomorphologically consistent and possibly have the same origin as thermokarst related landforms on Earth. Terrestrial thermokarst: Thermokarst landforms occur in areas where a disturbance in the thermal regime of ice-rich (excess ice) permafrost induces thaw. This leads to the melting of ground ice, the ponding of water, further melting of ground ice due to the high thermal capacity and conductivity of water, the subsequent collapse of surficial material and the formation of pits and depressions. A widespread contributing factor to thermokarst degradation is the presence of thermal contraction polygons underlain by ice-wedges [1], hence the close spatial association between the two landforms. During the warmer seasons water accumulates at polygon junctions (fig. 2) due to the melting of snow and exposed or near-surface ice-wedges or ground ice. The higher thermal capacity and thermal conductivity of water invariably causes the melting of ground ice and promotes further thermal erosion of ground ice. The loss of water through drainage, evaporation, or sublimation forms a pit at the junction of polygons. Pits and polygons in western UP: Polygon pits (fig. 1) and polygonal terrain (fig. 1) are widespread in western UP. The polygons have trough-to-trough diameters that range between ~50–150m [2]. Polygon pit size ranges between ~14-58m (mean diameter=36 m, n=77) in diameter and their shape varies from circular to slightly elongate. Polygon pit depth varies between 5–36m (mean depth=17.4, n=77). In many instances, the polygon pits exhibit a beaded pattern. Most pits occur at polygon junctions. Interspersed among the polygon pits are larger depressions (~200-3500m in diameter) that occur in isolation or coalescence. Geological interpretation: Depressions similar in morphology to the polygon pits in UP are common in the area surrounding the Tharsis rise. Such features, called pit craters, form when surface material collapses into a sub-surface cavity created by endogenetic processes (e.g. [3], [4]). Due to their origin, pit craters commonly occur within graben systems or near areas that display extensional or volcanic stresses such as fault lines, lava tubes and collapsed magma chambers (e.g. [5], [6]. Wyrick et al. [7] suggest that the polygon pits of UP are the product of processes similar to those of pit crater formation near the Tharsis region. However a geomorphological analysis between the pit craters and the polygon pits reveals several discrepancies.

Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.