Active Boulder Falls in Terra Sirenum, Mars: Constraints on Timing and Causes

Abstract

The last decade has seen significant improvements in the identification and monitoring of active surface processes on Mars. Repeat observations have allowed the study of a wide range of features and processes. Many of these studies have concentrated on changes observed on the slopes of crater walls, particularly of gully (e.g., Dundas et al., 2015) and recurring slope lineae (RSL) features (e.g., McEwen et al., 2014). To date, none of these active features have been driven by endogenic processes, with environmental conditions instead the most likely explanation for change. Some of the most significant changes involving boulder movement have been identified at high latitudes on Mars, where a number of environmental processes are likely enhanced (Dundas et al., 2019). To date, such significant boulder movement has not been studied in detail at lower latitudes on Mars.On Earth, boulder size and fall frequency have been used as proxies for earthquake location (e.g., Keefer, 1984). On Mars, this correlation has been applied to studies of boulder populations in the graben of Cerberus Fossae (Brown & Roberts, 2019;Roberts et al., 2012), in addition to proposed evidence of recent, localized seismic activity in Valles Marineris, and Jezero Crater (Senthil Kumar et al., 2019;Sinha et al., 2020). However, these studies were restricted to images representing a single time period, and thus no active boulder transport was identified. Here we use repeat orbital images to study significant active boulder transport in an unnamed near-equatorial crater in Terra Sirenum (Figure 1). Dark flows on the crater walls are made mostly of meter-scale boulders, and through a rigorous co-registration procedure, we have identified several areas of active boulder transport, and discuss possible causes for the activity.

Boulder Fall Ejecta: Present Day Activity on Mars

“…From our survey, we find rockfall triggered by wind, thermal cracking and seismic shaking are reasonable triggers for the recent falls causing BFE. Our observations suggest that the present day occurrence of boulder falls is wide spread, and that they are happening more frequently (Figures 4d and 4e) than previously reported (Dundas & Daubar, 2020; Grindrod et al., 2021).…”

“…Repeat temporal imaging has shown that boulder falls are ongoing on Mars, as first observed by the Mars Global Surveyor—Mars Orbiter Camera (Malin & Edgett, 2001) images from the southern hemisphere and Valles Marineris (https://www.msss.com/mars_images/moc/2005/09/20/bouldertracks/). Subsequently, several studies have used repeat temporal imaging using HiRISE to identify and study recent boulder falls (Dundas & Daubar, 2020; Dundas et al., 2019; Grindrod et al., 2021). The boulder fall tracks are predominantly present on crater walls and floors, but can originate from any steeply sloping surface (Bickel et al., 2020; Kumar et al., 2019; Sinha et al., 2020; Van der Bogert & Plescia, 2014).…”

Planetary geomorphology

“…A consequence of rock breakdown is rockfalls, which have been observed to occur in repeat imaging of Mars (Grindrod et al, 2021;Vijayan et al, 2021) (Figure 9b). Roll/bounce marks left in the regolith in the wake of boulders (Figure 9c) have shown rockfall to be a recently active process on the Moon (Arvidson et al, 1975;.…”