Recent (Late Amazonian) enhanced backweathering rates on Mars: Paracratering evidence from gully alcoves

Abstract

The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Abstract Mars is believed to have been exposed to low planet-wide weathering and denudation since the Noachian. However, the widespread occurrence of alcoves at the rim of pristine impact craters suggests locally enhanced recent backweathering rates. Here we derive Late Amazonian backweathering rates from the alcoves of 10 young equatorial and midlatitude craters. The enhanced Late Amazonian Martian backweathering rates (10 −4 -10 −1 mm yr −1 ) are approximately 1 order of magnitude higher than previously reported erosion rates and are similar to terrestrial rates inferred from Meteor crater and various Arctic and Alpine rock faces. Alcoves on initially highly fractured and oversteepened crater rims following impact show enhanced backweathering rates that decline over at least 10 1 -10 2 Myr as the crater wall stabilizes. This "paracratering" backweathering decline with time is analogous to the paraglacial effect observed in rock slopes after deglaciation, but the relaxation timescale of 10 1 -10 2 Myr compared to 10 kyr of the Milankovitch-controlled interglacial duration questions whether a paraglacial steady state is reached on Earth. The backweathering rates on the gullied pole-facing alcoves of the studied midlatitude craters are much higher (∼2-60 times) than those on slopes with other azimuths and those in equatorial craters. The enhanced backweathering rates on gullied crater slopes may result from liquid water acting as a catalyst for backweathering. The decrease in backweathering rates over time might explain the similar size of gullies in young (<1 Ma) and much older craters, as alcove growth and sediment supply decrease to low-background rates over time.

Thermal and Mechanical Responses Resulting From Spatial and Temporal Snow Cover Variability in Permafrost Rock Slopes, Steintaelli, Swiss Alps

“…The duration of the snow‐free period influences rock stability. This can have significant impacts on rock fatigue (Jia et al , ) and affects the thermal controls of effective rock wall retreat rates (Siewert et al , ; Krautblatter and Moore, ; de Haas et al , ). Warming rock expands uniformly and fractures narrow (Cooper and Simmons, ), whereas cooling rock contracts and fractures open.…”

CO 2 sublimation in Martian gullies: laboratory experiments at varied slope angle and regolith grain sizes

“…We also consider it possible that the mechanism of CO 2 sublimation-triggered failures we observed in the laboratory could also have occurred under climate conditions different from those observed on Mars today, which may explain some of the sediment transport that has contributed to gully formation on timescales of millions of years (Reiss et al 2004;Schon et al 2009;de Haas et al 2015a). However, further modelling work to understand the plausible temporal and spatial extent of this process at the present day would be needed in order to confidently extrapolate this process into the past, an endeavour beyond the scope of this present work.…”

“…It should be acknowledged that whether this is a primary feature of the gully-forming process is under debate (cf. de Haas et al 2015a;Dickson et al 2015). The relationship between this weathering and the action of CO 2 condensation-sublimation cycles is an area for future work.…”

Mechanical weathering and rock erosion by climate‐dependent subcritical cracking

“…In particular, moisture is widely cited as a substantial contributor to rock breakdown. Strong empirical relationships have been extensively documented between moisture and associated weathering, regolith production (defined here as the conversion of bedrock into mobile sediment), and/or erosion [e.g., Burnett et al, 2008;Griggs, 1936;Haas et al, 2015;Hall, 1986;Larsen et al, 2014;Matsukura and Takahashi, 2000;Owen et al, 2011;Sass, 2005]. Overall, however, the mechanisms by which water-in either liquid or vapor form-influence mechanical weathering have remained unclear [Burke et al, 2007;Hall and Hall, 1996;Halsey et al, 1998;Mol and Viles, 2012;Sass, 2005].…”