Interaction of outburst floods with basaltic aquifers on the Snake River Plain: Implications for Martian canyons

Abstract

Idaho's Snake River Plain is underlain by a young sequence of basaltic lava fl ows that house one of the most conductive aquifers in the world and have been sculpted by at least three megafl oods in the last ~100 k.y. The timing and routing of these fl oods, and their interaction with the underlying aquifer, have taken on renewed signifi cance because they have carved amphitheater-headed dry canyons analogous to those found on Mars. In this study, we use cosmogenic 3 He and 21 Ne dating of fl ood-deposited boulders to show that the Big Lost River and Bonne ville fl oods were closely spaced in time at ca. 22.3 and ca. 17.5 ka, respectively. Most of the dry canyons record signifi cant erosion during the Big Lost River fl ood, despite its much smaller magnitude than the later Bonne ville fl ood. We explain this puzzling observation by proposing a composite erosion model in which erosion during the Big Lost River fl ood was partially accomplished by routing of fl oodwaters through the Snake River Plain aquifer. Topographic analysis shows that Big Lost River fl oodwaters ponded in the Terreton Basin, infi ltrated into the aquifer, and likely emerged as return fl ow in watersheds upstream of the dry canyons. We propose that sustained and focused erosion associated with return fl ow over months to years could explain the unique morphology of some dry canyons. Such a model also explains why most dry canyons are coincident with springs and surface watersheds, and it may provide a model for the way in which morphologically similar canyons evolved on Mars.

Geological Evidence of Planet‐Wide Groundwater System on Mars

“…Since only a few valleys on Earth (e.g., Schumm et al, 1995) are thought to be affected exclusively by seepage erosion (e.g., Lamb et al, 2006) and the component of water flow erosion cannot be excluded, we believe that a composite discharge model is a plausible formation mechanism for the amphitheater-headed valleys studied in this work. There is no evidence of large surficial floods in the intercrater plains around the craters or of flows cutting the craters from outside, as also suggested by Amidon and Clark (2015). Furthermore, a composite discharge model (overland flow and groundwater) is also consistent with the model proposed by Andrews-Hanna et al (2007 and terrestrial field observation (Kochel & Piper, 1986).…”

“…It implies that valleys could be formed by groundwater discharge on a more rapid time scale than required by a seepage weathering mechanism (Lamb et al, ). It also suggests that the lower latitude valleys studied in this work could potentially be attributed to groundwater recharge or from nearby craters (Amidon & Clark, ).…”

“…Nonetheless, other formation mechanisms of these valleys cannot be excluded on the basis of their morphology alone. Several mechanisms such as groundwater seepage (Goldspiel & Squyres, 2000;Howard, 1986;Kochel & Piper, 1986;Malin & Carr, 1999;Schumm et al, 1995), overland flow (Lamb et al, 2008;Lapotre & Lamb, 2018), and combinations of the two (Amidon & Clark, 2015;Laity & Malin, 1985;Pelletier & Baker, 2011) have been suggested to explicate the genesis of amphitheater-shaped valleys both on Earth and Mars. Pelletier and Baker (2011) applied numerical models to show that amphitheater headwalls are diagnostic of seepage erosion.…”

Substrate controls on valley formation by groundwater on Earth and Mars

“…However, valley morphology is not a unique indicator of formation process (Lamb et al, 2006). Groundwater seepage (Schumm et al, 1995), overland flow (Lamb et al, 2008), and combinations of the two (Laity and Malin, 1985;Pelletier and Baker, 2011;Amidon and Clark, 2015) have all been proposed to explain the formation of amphitheater-shaped valleys on Earth and Mars (Fig. 1), and they have distinct astrobiological implications.…”

Canyon formation constraints on the discharge of catastrophic outburst floods of Earth and Mars

“…In particular, amphitheater-headed canyons that have roughly uniform widths are thought to form by upstream propagation of the headwall [Lamb and Dietrich, 2009;Petroff et al, 2011]. In the absence of quantitative mechanistic models for headwall retreat, radically different flow configurations have been proposed to explain the formation of various amphitheater-headed canyons on Earth and Mars, such as both long-lived [Harrison and Grimm, 2005;Pelletier and Baker, 2011;Petroff et al, 2011] and catastrophic [Amidon and Clark, 2014] groundwater seepage erosion, as well as catastrophic overland flow and waterfall erosion [Baker and Milton, 1974;Carr, 1979;Komatsu and Baker, 1997;Lamb et al, 2006;Warner et al, 2010].…”