Interweaving Recurring Slope Lineae in Raga Crater, Mars

Recurring slope lineae (RSL) are unique features on the Martian surface whose formative mechanisms and overall geomorphic expression are still poorly understood. While many appear linear, a small subset— notably in Martian craters such as Raga— display an interweaving morphology. This morphology has not been discussed at length in the literature and raises several questions about the nature of recurring slope lineae, and specifically about their geomorphic expression. We seek to determine whether interweaving slope lineae can provide insight into the formative nature of RSL.

Approximately 87% (198 of 228) of RSL were found to contain just a single channel. while ~10% (23 of 228) had two channels, ~2% (5 of 228) had three channels, and less than 1% (2 of 228) had four channels. Conversely, 4% of channels (10 of 267) were determined to be sinuous; the highest sinuosity ratio found was 1.204. None were classified as meandering. Additionally, most sinuous channels— six of ten— were found to be part of multi-channel RSL systems. However, only four anabranching RSL contained sinuous channels. Six sinuous channels were part of the four multi-channel lineae, whereas four sinuous channels were part of single-channel lineae.

Of the seventy-seven channel bifurcations measured, approximately 51% (39 of 77) were found on slopes that became shallower in the few meters around channel bifurcation. By contrast, only around 27% (21 of 77) of the channel confluence points were on slopes that became shallower around where the channels reconvened. Slope angle therefore appears to play an integral role in channel bifurcation, reconvening, and in the propensity for RSL interweaving more broadly.

We postulate that the interweaving exhibited by recurring slope lineae helps to further constrain their formative mechanisms as either fully aqueous in form, or as a dry, channelized flow of sediment down sinuous sub-resolution channels. Our research suggests that changes in slope angle near the bifurcation point of slope lineae are associated with the interweaving patterns seen in RSL, and that higher sinuosity in those channels may also influence the interweaving seen in these features.