Thermal anomalies on pit craters and sinuous rilles of Arsia Mons: Possible signatures of atmospheric gas circulation in the volcano

Abstract

[1] Seven circular depressions named as pit craters were found in northern flank of Arsia Mons, and we report 76 new ones in the southern flank of the volcano. Their diameters range from 100 m to 1300 m and depths range from 22 to 500 m. THEMIS-IR data reveal that some of these pit craters are 10 K warmer than the surrounding surface during night and are referred as Thermally Distinct Pit (TDP). Nighttime surface temperature variations of 10 K at this scale are common on Mars and may result from a combination of geometrical factors and/or variations of thermophysical properties. However, several observations appear to be difficult to reconcile with this view. We have thus explored the conditions for the occurrence of $40 km long subsurface air flow through the volcano apron and its consequences on surface temperatures. Our numerical simulations assume that cold air penetrates the apron through a slope break. It then flows upslope affecting a thickness of 6 km and finally exits 40 km away through warm pit craters and sinuous rilles. An extremely high horizontal permeability of 10 À4 m 2 and a vertical permeability of 10 À8 m 2 are used considering the anisotropic media resulting from the accumulation of lava flows and ash/scoria deposits. Without unequivocally ruling out a possible contribution of geometrical factors and thermal properties variations, these numerical simulations show that the ascending convective flow provides, at the surface, a heat flow able to sustain an excess temperature of $10 K.

Atypical pit craters on Mars: New insights from THEMIS, CTX, and HiRISE observations

“…We find no correlation between d / D ratios and floor/surface temperature differences, which is consistent with results from Lopez et al [], except to note that APCs with larger temperature differences occur in pits with d / D ratios greater than 0.4. However, correlations that do exist may be lost in the range and sparsity of available TIR data.…”

“…These effects become more prominent as the solar incidence angle increases. A detailed mathematical description of cylindrical and parabolic pits, and of their respective shadow shapes, is provided in Appendix A from Lopez et al []. Applying this technique, we find that APCs with (observed) shadow boundaries on their floors exhibit cylindrical morphologies in all cases.…”

“…Lopez et al [] present an alternative hypothesis to explain APC floor‐temperature behaviors. They propose that APC floors, and columns immediately beneath them, consist of collapsed rubble with much higher bulk porosity than the surrounding bedrock, thus creating an effective vent through which warmer subsurface air can percolate and escape.…”

“…Haruyama et al [], Robinson et al [], and Wagner and Robinson [] discuss a small collection of deep lunar pit craters that might host laterally extending cave entrances. Wyrick et al [] provide a detailed examination of pit‐crater chains on Mars, Lopez et al [] conduct a thermal investigation on Martian pit‐crater thermal anomalies, and Thomas [] examines pit chains on Mars' moon Phobos, which are subsequently referred to as “drainage pits” in Horstman and Melosh []. On asteroids, Buczkowski et al [] discussed pits on 433 Eros, Veverka et al [1994] found pits on 951 Gaspra, and Sullivan et al [] found them on 243 Ida.…”

Electric potential anomaly induced by humid air convection within Piton de La Fournaise volcano, La Réunion Island

“…Several studies suggest that pluri-kilometric subsurface airflow can occur within both active or inactive volcanic structures (Weeks, 1987;Ross et al, 1992;Lu et al, 1999;Ohsawa et al, 2000;Antoine et al, 2011;Lopez et al, 2012). In fact, the structure of PdF is not so different from the structure of Formica Leo.…”