Martian gullies are kilometre-scale landforms consisting of an alcove, channel and depositional fan. They are among the youngest landforms that may have formed by liquid water and are active today. Understanding their formation is thus critical for resolving Mars’ most recent climatic history and potential to sustain life. Gullies on Mars have been hypothesized to have formed by either the action of liquid water and brines or the action of sublimating carbon-dioxide (CO₂) ice. They strongly resemble terrestrial systems formed by aqueous debris flows, having similar sedimentology, morphology, and morphometry. Yet, new deposits have formed within multiple gullies across Mars over the past decade, and we cannot reconcile these flows with the low availability of atmospheric water and the triple point of water under present martian conditions. These flows do, however, occur in winter when temperatures are below the CO₂ condensation point, and CO₂-ice has been observed in many gullies during time of activity. But can CO₂ sublimation support and fluidize mass flow on Mars and form deposits similar to terrestrial debris flows? Here, I present novel experiments where we operate small-scale mass-flow flumes inside Mars chambers at Aarhus University (Denmark) and the Open University (UK). In these chambers Martian atmospheric conditions can be simulated, which is crucial for fluidization of mass flows since volume expansion, and therefore gas flow rate, by CO₂-ice sublimation is much larger under the low atmospheric pressure of Mars (8 mbar) than under the atmospheric pressure of Earth (1000 mbar). These experiments reveal that CO₂ sublimation under martian atmospheric conditions can fluidize mass flows by generating elevated pore pressures reducing intergranular friction, resulting in lobate deposits with levees, as observed in martian gullies. These findings show that CO₂-sublimation processes can explain our observations in active Martian gully systems today, which has far-reaching implications for the search for potential liquid water on Mars as well as the interpretation of planetary landforms on other planetary bodies. In particular, they show that on planetary bodies unlike Earth, landforms may be created that look similar to those found on Earth but are actually produced by disparate and so-far unknown processes.

How to cite: de Haas, T., Roelofs, L., Conway, S., McElwaine, J., Merrison, J., Patel, M., and Sylvest, M.: Sublimation-driven formation of recent mass flows on Mars: experimental tests in low-pressure environments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1451, https://doi.org/10.5194/egusphere-egu23-1451, 2023.

As detailed in a recent journal publication by the authors of this abstract, women have made significant contributions in the fluvial, aeolian, and (cryo)volcanic subdisciplines of planetary geomorphology, despite undeserved challenges to their participation. Some women—in particular, women of color—are highlighted in this work to show a part of these foundational contributions. As the latter half of the 20th century was a revolutionary time for terrestrial geomorphology and the inception of the discipline of planetary geomorphology, we focused our research into these contributions on women scientists who were working during this time. We also focused on women working in our scientific subdisciplines so that we could provide proper context for their work. These contributions have occurred both as discoveries in terrestrial geomorphology leading to follow-on discoveries in planetary geomorphology and through serving as educators and role models. With women increasingly achieving positions of influence both in the geo- and planetary sciences as in American society, this research allows us to celebrate these contributions of women and particularly women of color while looking forward to a more complete record of their past contributions and greater future achievements.

How to cite: Burr, D., Diniega, S., Quick, L., Gardner-Vandy, K., and Rivera-Hernandez, F.: Foundational women in planetary geomorphology: Some contributions in fluvial, aeolian, and (cryo)volcanic subdisciplines, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2912, https://doi.org/10.5194/egusphere-egu23-2912, 2023.

Debris flows are extremely rapid, flow-like landslides composed of fine and coarser-grained components, boulders, woody debris as well as water. They are characterized by large impact forces as well as long runout distances and are one of the most dangerous types of mass movements in mountainous regions. More detailed field-scale measurements of hazard-related parameters in natural debris flows are required to better understand the fundamental mechanisms governing their motion and, ultimately, reduce the associated risks.

In the present work, we analyzed two debris-flow events using timelapse point clouds from a high-resolution, high-frequency 3D LiDAR sensor (Ouster OS1), which we installed at the WSL debris-flow monitoring station in the Illgraben catchment (Valais, Switzerland). We developed and applied both manual and automated algorithms to derive critical hazard-related parameters – including front and surface velocities, cross-sectional area, discharge and event volume – at an unprecedented level of detail.

In both events, we observed that surface velocities measured directly behind the front exceeded the front velocity (by a factor of 1.75x on average), which likely led to the formation of the bouldery front. We further found that different objects traveled at systematically different velocities: large, rolling boulders were moving at 0.6–0.8 the velocity of floating woody debris during both analyzed events. This observation was likely caused by these different objects sampling the vertical velocity profile at different depths, and thus provided quantitative information about the shape of the velocity profile.

We further applied automated surface velocity estimation techniques as well as automated cross-sectional area measurements to derive the discharge over time and in space at three different, closely spaced channel sections upstream of a check dam. We accounted for potential changes in the shape of the channel bed by considering different “channel geometry scenarios” (based on pre-event and post-event scans) and included presumed changes in the vertical velocity profile – based on our findings mentioned above – in our discharge derivation. We assessed the reliability of these different scenarios by comparing the discharge values at different sections, which allowed us to infer potential changes in the channel bed geometry.

The LiDAR data analyzed in this work is unique because it allows for a truly 3D, high-resolution investigation of moving debris flows at sub-second intervals. The developed methods will be applied to LiDAR data from additional monitoring stations and events at the Illgraben, which should allow for further inference into the internal dynamics of debris flows. Eventually, this might enhance our understanding of the fundamental debris-flow mechanisms, help to optimize numerical as well as empirical modeling approaches, improve hazard mitigation in general and reduce the risk posed by flow-like landslides in the future.

How to cite: Spielmann, R. and Aaron, J.: High-resolution 3D LiDAR measurements of natural debris flows at sub-second intervals; Illgraben, Switzerland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5357, https://doi.org/10.5194/egusphere-egu23-5357, 2023.

Preserved geomorphological landforms on the surface of Mars indicate the presence of abundant liquid water in the early history of Mars. Many of these geomorphic features were developed by erosion and deposition of sediments by water. It is therefore important to understand how fluvial sediment transport works on Mars and how it is different from Earth. Due to the lower gravity on Mars water flows down slope with less energy, resulting in lower bed shear stresses and flow velocities. Nonetheless, fluvial sediment transport is more efficient. Due to the lower gravity the mobility of the sediment is higher. Larger grains are brought into motion and suspension (Komar, 1980; Burr et al., 2006) and the magnitude of suspended transport is significantly higher (Amy and Dorrell, 2021), as is the total transport flux (Braat et al., 2022). In addition, the settling of sediment is slower, resulting in larger transport distances on Mars compared to Earth. Based on the differences in entrainment due to gravity, different grain size mixtures are transported and settle out in a different manner (Braat et al., 2022). Therefore, the geomorphology and stratigraphy of geomorphic landforms might be different than we expect from Earth observations. In this study, we investigate how fluvial geomorphology differs on Mars through sediment transport calculations on Mars and our terrestrial knowledge and experience.

We use two methods: 1) We use standard hydraulic equations to calculate hydrodynamic conditions based on a slope, channel width and discharge. From these conditions we calculate sediment transport fluxes using multiple sediment transport predictors for both bedload and suspended load. Total load predictors are not suitable for Mars, as they do not account for a variable gravity effect with grain size. 2) We also run numerical hydro-morphodynamic model scenarios to compare the evolution of fluvial geomorphic features with Earth and Mars gravity. We use the software package Delft3D (Lesser et al., 2004), and amended the code to work on Mars.

Simple sediment transport calculations indicate that the sediment fraction at the bedload-suspended load boundary is most affected by gravity. In our examples transport could be up to 6 times higher for this fraction. Overall, the magnitude of the total transport flux on Mars is also bigger, predominantly because of increased suspended transport. As the bedload fraction is the ‘channel-building’ fractions and suspended transport determined channel-floodplain interaction, we hypothesise that floodplain deposition will increase. Additionally, with more sediment entering the floodplain levee accretion will increase, as will cut-off infilling and crevasse splays. We also hypothesise that increased suspension will reduce channel migration, reduce branching, increase the avulsion rate, and create more sinuous, narrow channels (Nicholas, 2013). The preliminary model outcomes confirm our hypothesis that depositional slopes are lower due to longer advections lengths related to lower settling velocities. For example, this will transport more sediment to the delta front and pro-delta, impacting deltas foresets (van der Vegt et al., 2016). Finally, the models agree that geomorphic features develop faster on Mars.

How to cite: Braat, L., Brückner, M., Baar, A., Lamb, M., and Sefton-Nash, E.: Differences in Fluvial Geomorphology between Earth and Mars, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8070, https://doi.org/10.5194/egusphere-egu23-8070, 2023.