Formation of periodic bedrock ridges on Earth

Periodic Bedrock Ridges at the ExoMars 2022 Landing Site: Evidence for a Changing Wind Regime

“…The fact that the ridges are mostly carved into the bedrock narrows down the possible formation process to aeolian erosion. Candidate resulting landforms are either yardangs, which are streamlined hills eroded by wind or periodic bedrock ridges (PBRs), which are bedform‐like erosional features (Goudie, 2007; Hugenholtz et al., 2015; Laity, 2009; Montgomery et al., 2012). The crestlines of the ridges are not streamlined, have Y junction terminations (typical in aeolian bedforms [McKee, 1979; Werner & Kocurek, 1999]), and do not resemble yardangs at any of their formational stages (Wang et al., 2018).…”

“…Their overall morphology and wavelength are rather consistent with PBRs (Montgomery et al., 2012). PBRs were hypothesized to form from the direct sand abrasion of the surface bedrock (Montgomery et al., 2012) or by bedrock erosion seeded by megaripples (Hugenholtz et al., 2015). In the latter hypothesis, the erosion of the underlying bedrock starts in ripple troughs where the substrate is exposed (see Figures 10a and 10b in Hugenholtz et al., 2015).…”

Aerodynamic roughness height for gravel-mantled megaripples, with implications for wind profiles near TARs on Mars

“…The largest gravel-mantled megaripples seem to affect the wind profile more like a sand dune than like a typical sand ripple, which has implications for the roughness height expected near Transverse Aeolian Ridges (TARs) on Mars, a non-genetic term applied to large aeolian bedforms that are wide-spread across the planet that may have formed either as small sand dunes or large wind ripples (Bourke et al, 2003;Wilson and Zimbelman, 2004;Balme et al, 2008;Berman et al, 2011). The Puna has also been proposed as an analog to investigate a possible genetic relationship between the gravelmantled megaripples and 'periodic bedrock ridges', erosional bedforms with physical dimensions similar to the gravel-mantled megaripples; periodic bedrock ridges were first identified on Mars (Montgomery et al, 2012) but they have also been studied in the Puna (Hugenholtz et al, 2015). The differences of atmospheric density and gravity between Earth and Mars (Greeley and Iversen, 1985, pp.…”

Supplemental Material: Eolian megaripple stripes

“…The region's complex geology means that grains being transported are of varying densities, including pumices < 1000 kg/m 3 and basalt grains ~ 3000 kg/m 3 (de Silva et al, 2013). This presents an enormous complication in understanding the region's aeolian transport (Hugenholtz et al, 2015). The complexity of aeolian transport in areas with multiple lithologies is under-researched, and the simplifying assumption of equal densities is often made despite the inaccuracies that such an assumption introduces.…”