New Mexico Geological Society Annual Spring Meeting — Abstracts

Recurring slope lineae (RSL) are unique features on the Martian surface whose formative mechanisms and overall geomorphic expression are still poorly understood [1]. 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; specifically about the geomorphic expression of interweaving RSL. We seek to determine whether interweaving slope lineae can provide insight into the formative nature of RSL, and postulate that the interweaving exhibited by recurring slope lineae does help 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 also 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 influence the interweaving nature of these features.

Approximately 87% (198 of 228) of RSL were found to contain just a single channel. Approximately 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 of the channels cataloged as sinuous— 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 the channel bifurcation. By contrast, only around 27% (21 of 77) of 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.

This research is applicable not only to extraterrestrial hillslope processes, but to terrestrial hillslope processes and specifically to hillslope failure— especially in drier, more arid terrestrial regions, such as the desert southwest in the United States. While not a perfect analogue for the Martian surface due in part to the terrestrially higher temperatures and moisture content, states such as New Mexico nonetheless approximate generic Martian conditions more closely than their more vegetated and humid terrestrial counterparts. As such, understanding the downslope movement of material on planets such as Mars can provide geomorphologists, urban planners, and hydrologists with a greater understanding of slope processes in dry, arid environments, informing decisions about environmental hazards and risk mitigation strategies throughout both the state of New Mexico and the region more broadly.

References:

1. [1] Stillman, D. E. et al. (2020) Icarus, 335 (August 2019), 113420.