IS EROSION BY LAVA IMPORTANT ON MARS?

It can be difficult to distinguish the roles of lava and water in channels that have had both fluids run through them. This is the case in several Mars outflow channels such as Athabasca Valles, Kasei Valles, Marte Vallis, Rahway Valles, Grjótá Valles, and Mangala Valles [1]. This has led to some papers suggesting that even the largest flood channels on Mars were carved by lava [e.g., 2]. Recent studies have shown that thermal erosion by lava should be limited on Mars [3]. At the same time, there is strong observational evidence that the lava flow in Kasei Valles caused localized erosion on the hectometer scale but the main channels were carved by catastrophic aqueous floods [4]. We continue to investigate Athabasca Valles where it is plausible that there was no water flood. Instead, an existing depression in front of a wrinkle ridge may have been modestly deepened by mechanical erosion by a turbulent flood of lava. Between the Athabasca and Kasei Valles examples, we are starting to assimilate a family of geomorphologic features that can be associated with water and lava erosion. Furthermore, we now have some quantitative measures of the conditions under which observable erosion by lava does and does not take place. This provides essential constraints for attempts to model erosion by lava and better understand the underlying physics. Unlike an aqueous flow, the erosion is unlikely to be due to abrasion. Instead, mechanical plucking and bed-load traction maybe key processes. If this is correct, the mathematical expressions based on basal stress that are used to model stream erosion on Earth (e = k_bt^a [e.g., 5]) are likely to be applicable but the values for the parameters k_b and a may be quite different than for water on Earth.

[1] McEwen et al. (2012) LPSC Abstract #1612. [2] Leverington (2011) Geomorphology, v. 132, pp. 51-75. [3] Cataldo et al. (2015) J. Geophys. Res., v. 120, pp. 1800-1819. [4] Dundas and Keszthelyi (2014) J. Volcanol. Geotherm. Res., v. 282, pp. 92-102. [5] Whipple and Tucker (1999) J. Geophys. Res., v. 104, pp. 17661-17674.