REACTION OF CA SULFATES AND CHLORIDES IN THE MARTIAN NEAR SURFACE TO CREATE SINKHOLES AND DEBRIS FLOWS

Debris flow on Mars such as RSL and gullies could be related to reactions of sulfates and Cl salts as observed on Earth. Gypsum (CaSO₄ •2H₂O) reactions with halite (NaCl) on Earth are associated with sinkholes in evaporite deposits [e.g. 1]. As liquid water comes in contact with halite, it dissolves and forms a brine system. Dissolution of gypsum in contact with these brines occurs and then forms cracks, faults and porous features. Dissolution of extensive gypsum deposits can form large caves, such as those at Carlsbad caverns, NM. Formation and collapse of karst systems in Spain has occurred through dissolution of halite, gypsum and glauberite (Na₂Ca(SO₄)₂)) [2]. In that study, small collapse sinkholes (diameters <16 m) occurred through dissolution conduits at salt minerals causing sudden downward migration of material, while larger collapse sinkholes (diameters ~100 m) are attributed to progressive propagation of cavities through gradual dissolution of sulfates and Cl salts. Further, gypsum veins in stratovolcanoes have been associated with edifice collapse and debris flow [3]. Near surface gypsum and halite are observed in the Antarctic Dry Valleys where liquid water is mobile a few cm below the cold and arid surface [4]. Ice has been identified just below the surface in HiRISE images at several mid-latitude sites on Mars [5]. Melting of this near-surface ice on sun-facing slopes could be providing a small amount of liquid water that is adsorbed by Cl salts in the soil until a saturation point is reached and dissolution occurs. This Cl-brine could then further dissolve Ca sulfates in the regolith, releasing more debris and facilitating downslope flow of dry material as the liquid water sublimates when exposed to the surface.

[1] Yechieli et al. (2016) Hydrogeol. J., 24, 601-612.

[2] Galve et al. (2009) Geomorph., 108, 145-158.

[3] Zimbelman et al. (2005) Chem. Geol., 215, 37-60.

[4] Englert et al. (2015) AGU, Abs #62033.

[5] Dundas et al. (2018) Science, 359, 199-201.