How to cite: Yazici, I. S. and Klimczak, C.: Polygonal impact craters reveal a global fracture pattern on Mercury, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3585, https://doi.org/10.5194/egusphere-egu21-3585, 2021.

Long runout landslides are a particular type of mass-wasting phenomena that belongs to the category of surface processes associated with rapid strain rates. The reduction of friction that has to be invoked to explain their high velocities and exceptional travel distance over nearly horizontal surfaces has yet to find satisfactory explanation. Inspired by fault mechanics studies, thermally-activated mechanisms can explain the dynamic frictional strength loss during sliding along the initial failure surface and the early development of velocities higher than expected. However, as slides continue moving along nearly horizontal valley floors, the weakening mechanisms required to sustain their exceptional behaviour are less certain.

Long runout landslides are found ubiquitous in our solar system and the slow erosion rates that operate on extraterrestrial planetary bodies allow the preservation of their geomorphological record. The availability of the latest high-resolution imagery of the surface of Mars and the Moon allows to conduct detailed morphometric analysis not so granted on our planet. On the other hand, on Earth, the partial loss of the geomorphological record due to fast erosion rates is compensated by the accessibility of sites that enable us to conduct field work. In order to better understand the mechanisms responsible for the apparent friction weakening we use a comparative planetary geology approach, in the attempt to link the morphology and the internal structures of long runout landslide deposits to the mechanisms involved during the emplacement of such catastrophic events.

We focused on the distinctive longitudinal ridges that mark the surface of the landslide deposits. The formation mechanism of longitudinal ridges in long runout landslides has been proposed to require ice, as this low friction material would allow the spreading of the deposit, causing the development of longitudinal ridges by tensile deformation of the slide. However, ice-free laboratory experiments on rapid granular flows have demonstrated that longitudinal ridges can form as a consequence of helicoidal cells that generate from a mechanical instability, which onset requires a rough surface and a velocity threshold to be surpassed. Moreover, such experiments have showed that the wavelength of the longitudinal ridges is always 2 to 3 times the thickness of the flow.

We here present the results from three case studies: the 63-km-long Coprates Labe landslide in Valles Marineris on Mars; the 4-km-long El Magnifico landslide in Chile, Earth; and the 50-km-long Tsiolkovskiy crater landslide, at the far side of the Moon. We found that the wavelength of the longitudinal ridges is consistently 2 to 3 times the thickness of the landslide deposit, in agreement with experimental work on rapid granular flows. The recurrence of such scaling relationship suggests a scale- and environment-independent mechanism. We discuss the applicability of high-speed granular flow convection-style mechanisms to long runout landslides and speculate on the existence of an alternative vibration-assisted mechanism.

How to cite: Magnarini, G., Mitchell, T., Grindrod, P., and Goren, L.: Longitudinal Ridges in Long Runout Landslides: on the Applicability of High-Speed Granular Flow Mechanisms., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4822, https://doi.org/10.5194/egusphere-egu21-4822, 2021.

Landslides are common features on the surface of Mars. They have morphologies that resemble debris slides, mudflows [1], or giant rock avalanches [e.g., 2] on Earth. They can mobilise large quantities of material up to 10¹² m³ and spread over areas of up to 10⁹ m² [e.g., 3].

The topography before the landslide event occurred is required to both estimate the volume of mobilised material and quantify the distribution and thickness of the deposit. The mass distribution of the deposit can also be used to compare with 3D flow simulations of landslides [e.g. 1, 3]. However, on Mars there are no landslides that have known topographic data before the event occurred, hence we have to rely on topographic reconstruction.

This type of reconstruction, which we have already carried out using HiRISE (High Resolution Imaging Science Experiment) Digital Elevation Models (DEM) with 1-2 m vertical resolution [e.g., 1], has never been undertaken using DEMs with 4-5 m vertical resolution derived from CaSSIS (Colour and Stereo Surface Imaging System) stereo pairs [4]. CaSSIS uses a 180° camera rotation to capture stereo images of a given site in a single pass. DEMs are then generated using 3DPD (three Dimensional reconstruction of Planetary Data) software [5].

Our aim is to test whether a landslide reconstruction can be carried out with a CaSSIS DEM. For our purpose we use a 6 km long landslide in Baetis Chaos region, Mars.

Our reconstruction consists of three main steps: 1) We first calculate contour lines. 2) Reconstructed contour lines are then drawn by connecting contour lines on either side of the boundary taking into account the overall topography outside the landslide. 3) Then, the reconstructed contour lines are converted into points at intervals equal to the spatial resolution of the DEM. These points are then interpolated using a natural neighbour algorithm to calculate a new DEM without the landslide. We were able to estimate that the landslide in Baetis Chaos has a volume of 10⁸ m³ and the deposit has a maximum thickness of 200 m using CaSSIS data.

Our successful reconstruction using a CaSSIS DEM increases the potential coverage of high-resolution stereo-topographic data beyond those already available with CTX and/or HiRISE. The resolution CaSSIS DEMs fills a gap in the topographic data currently available for studying landslides. Landslides > 15 km long can be studied with MOLA or HRSC data, and landslides < 5 km long can be studied using HiRISE data. Now, landslides and other landforms 5-15 km can be studied using CaSSIS data with equivalent quality to CTX stereo-topography.

Acknowledgement: CaSSIS is a project of the University of Bern, with instrument hardware development supported by INAF/Astronomical Observatory of Padova (ASI-INAF agreement n.2020-17-HH.0), and the Space Research Center (CBK) in Warsaw.

References: [1] A. Guimpier et al. (In review) PSS. [2] G. Magnarini et al. (2019) Nature Communications. [3] G.B. Crosta et al. (2018) ESS, 5, 89–119. [4] A. Lucas et al. (2014) Nature Communications. [5] E. Simioni et al. (In press) PSS.

How to cite: Guimpier, A., Conway, S., Pajola, M., Lucchetti, A., Simioni, E., Re, C., Mangold, N., Thomas, N., and Cremonese, G. and the CaSSIS team: Pre-landslide topographic reconstruction using a Digital Elevation Model from CaSSIS onboard the Trace Gas Orbiter., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4803, https://doi.org/10.5194/egusphere-egu21-4803, 2021.

The 125-km-diameter Hale impact crater is located in the southern hemisphere of Mars and has been dated to 1 Ga (Early to Middle Amazonian; Jones et al., 2011). It is thought to have penetrated the martian cryosphere, because it hosts landforms indicating volatile mobilisation post-impact: its ejecta are lobate and bear channels, and the interior is pervasively pitted and hosts alluvial fans (Collins-May et al. 2020; El-Maarry et al., 2013; Jones et al., 2011; Tornabene et al., 2012). Here, we test the hypothesis that conical mounds found within the ejecta are “molards” by comparing them to terrestrial analogues. Molards are conical mounds of debris resulting from the degradation of blocks of ice-rich material which have been mobilised by a landslide and are found in periglacial environments (Morino et al., 2019).

Our study area (240x180 km) is in the South-East part of the Hale impact crater ejecta (36°–39°S, 36°–31°W). We analyse the spatial and topographic distribution of the conical mounds using orbital images from 25 cm/pixel to 15 m/pixel and measure their height, width and slope using 1 m/pixel elevation data. We then compare them to conical mounds on the deposits of the 2010 Mount Meager debris avalanche, Canada (Roberti et al. 2017) and of the 2000 Paatuut landslide in western Greenland (Dahl-Jensen et al. 2004).

The conical mounds of the Hale impact crater are located at the distal boundary of the thickest part of the ejecta blanket, which reflects the spatial distribution of mounds along the distal parts of the terminal lobe of the Mount Meager debris avalanche. Furthermore, mounds in the Hale impact crater have comparable shapes and flank slopes to molards in the Mount Meager and Paatuut case studies, but are one order of magnitude bigger. This size difference is consistent with the flow-depth that transported the blocks also being one order of magnitude bigger than on Earth.

We infer that conical mounds near the Hale impact crater are a result of fragmented blocks of ice-cemented regolith produced by the impact and transported by the ejecta flows, and finally degraded into cones of debris (molards) by the loss of interstitial ice. Our interpretation supports the prevailing hypothesis that the Hale impact event penetrated the martian cryosphere and further provides important constraints on the rheology of martian ejecta deposits that can be tested by future studies and in other locations on Mars.

We acknowledge financial support for the PERMOLARDS project from French National Research Agency (ANR-19-CE01-0010).

How to cite: Morino, C., Conway, S., Peignaux, C., Lucas, A., Svennevig, K., Butcher, F., Roberti, G., Philippe, M., and Collins-May, J.: Molards as an analogue for ejecta-ice interactions on Mars, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9628, https://doi.org/10.5194/egusphere-egu21-9628, 2021.

The presumably fluvially affected surfaces of Mars provide evidence of the variety of surface processes of the past of the planet. Throughout its history, the climate has enabled the presence of liquid water several times (perhaps periodically). Watercourses and mega-river systems have ruled the surface; their tracks are still recognizable in many places. The Argyre Crater might have served as the source of such a huge river system: the Uzboi–Ladon–Morava River System (ULM), during the Late Noachian. (Dohm et al 2015) ULM is therefore fundamentally different from most of the valleys and channels of Mars as it is not an amphitheatre-headed valley, it is composed of various types of sections, and its source is connected to a large crater. In this study Uzboi Vallis, a section of ULM was studied using data from the Mars Global Surveyor's Mars Orbiter Laser Altimeter (MOLA) data. A comparison is presented of Uzboi Vallis and its tributary, Nirgal Vallis. In addition to creating the stream orders of the valleys and traditional elevation profiles, we used the swath profile analysis method. The swath analysis is fundamentally different from elevation profiles that enhance the specific Martian conditions (impact cratering, the complete absence of the biosphere, less gravity). In addition to the swath analysis completely covering the two studied areas, several regions of the catchment were specifically analyzed. According to the results obtained, the Uzboi Vallis is at least partly tectonically modified. Based on these observations, in the northeastern part, half-graben structures are hypothesized. The method of swath profile analysis, previously not applied to Martian data, proved to be useful and provided interpretable data for the surface of a planet other than Earth.

Geomorphometric studies on terrain models are found to provide interesting information paving the way towards an in-depth understanding of this mega river system. Further analysis of the ULM is planned in the near future.

Dohm, J.M., Hare, T.M., Robbins, S.J., Williams, J.-P., Soare, R.J., El-Maarry, M.R., Conway, S.J., Buczkowski, D.L., Kargel, J.S., Banks, M.E., Fairén, A.G., Schulze-Makuch, D., Komatsu, G., Miyamoto, H., Anderson, R.C., Davila, A.F., Mahaney, W.C., Fink, W., Cleaves, H.J., Yan, J., Hynek, B., Maruyama, S. (2015): Geological and hydrological histories of the Argyre province, Mars. Icarus 253:66–98.

How to cite: Szilágyi-Sándor, A. and Székely, B.: Comparison of the Uzboi Vallis and Nirgal Vallis (Mars) using swath analysis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12574, https://doi.org/10.5194/egusphere-egu21-12574, 2021.

Titan, Saturn's moon, is the only body in our solar system besides Earth to have liquids on its surface in the form of lakes, rivers, and seas - although the liquids are mainly hydrocarbons like methane and ethane. The liquids on Titan appear to flow in similar ways to those on Earth and create comparable fluvial patterns such as meandering rivers and dendritic fluvial systems. This project utilizes SAR data obtained from the Cassini-Huygens mission via Titan Trek to identify networks of inferred fluvial systems. We focus on data swaths T28 and T29 surrounding Ligeia Mare and Kraken Mare between 210 and 360 Longitude in Titan’s northern hemisphere. Previous studies (e.g. Burr et al., 2013) interpreted fluvial networks, principally from radar-light features. We focus on radar-dark features, applying an automated technique from Yang et al (2015) to map networks of presumed fluvial origin and compare them with our own visual mapping. Yang et al. used these automated techniques to map various known fluvial systems on Earth that appear radar-dark. Our application of the technique to the Titan study area is successful in identifying features that we had mapped by hand and other features that we had not identified in our visual mapping. The technique was more successful for imagery with less noise and less successful as noise level increased. The automated technique shows great promise for more widespread, rapid identification and mapping of the fluvial network.

How to cite: Skaggs, E.: Automated Mapping of Radar-Dark Fluvial Features on Saturn's Moon, Titan, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5832, https://doi.org/10.5194/egusphere-egu21-5832, 2021.

The stratigraphy preserved in Earth’s sedimentary basins offers a record of how landscapes have evolved with time.  This stratigraphy provides insights into the dynamic processes that shaped the surface of the earth.  Fluvial stratigraphy contains many elements that can be used to recreate past conditions in ancient river channels.  Paleohydraulic reconstruction uses measurements of fluvial stratigraphy to model the conditions in the system that created them.  This allows us to answer questions related to water discharge, sediment flux, and duration of fluvial activity.  These are key questions when investigated in the context of Mars.  Paleohydraulic models can be used as compelling analogs for similar systems on Earth as well as Mars and other rocky planets.           

This study examines what the record of Oligocene-Miocene fluvial stratigraphy in northeastern Spain’s Ebro Basin can tell us about water discharge and sediment flux across distributive fluvial systems at a basin scale.  The Cenozoic stratigraphy of northeastern Spain’s triangular shaped Ebro Basin embodies a classic example of the formation of a closed sedimentary basin.  The Ebro Basin contains a number of remarkably well exposed fluvial sedimentary deposits.  These deposits outcrop as distinctive laterally contiguous channel sand bodies.  Clastic sediment supply in the Ebro Basin is largely governed by tectonic uplift and basin subsidence related to the Pyrenean orogen with peripheral contributions from the Catalan Coast and Iberian Ranges.  We test the idea that the record of conditions in the fluvial systems should reflect the record of lacustrine chemical sediments through sediment mass conservation.  In order to test this hypothesis measurements of bedform height, barform height, sediment size, and paleochannel dimensions were collected in the field.  Our paleohydraulic model uses previously derived theoretical and empirical relationships to recreate the conditions in these ancient fluvial systems.  These results are scaled up by accounting for drainage density and intermittency in order to address the principal question at a basin scale.  Paleodischarges from the fluvial sediments are comparable to those from river chemistry calculations for the lacustrine facies. 

How to cite: Geil-Haggerty, H.: Paleohydraulic investigation of the Ebro Basin: Implications for Mars, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6865, https://doi.org/10.5194/egusphere-egu21-6865, 2021.

The presence of delta deposits on Mars has been thoroughly demonstrated for decades and large scale mapping [1,2] highlighted the presence of several delta fans mainly located on the dichotomy boundary. While a previous delta inventory was compiled by Morgan et al. [3], we aim to update and finalize a complete mapping of delta deposits in order to allow the examination of the evolution and distribution of standing bodies of water on Mars. The objective of our project focuses on the production of a global catalogue of water-related features at the Martian surface, which are commonly studied separately or at smaller scales.

Globally, we located around 150 deltas among which many were not previously included in published literature [e.g. 1,2,4]. We then examined the deltas based on two main traits. Firstly, we measured the length of the feeding channels since it may be (i) a proxy for the duration of the aqueous activity in the channel-delta system, and (ii) proportional to the age of the delta [2]. The latter relationship links older deltas near Chryse Planitia (>3 Ga) to longer valleys, while younger deltas are usually fed by shorter valleys [2]. Secondly, we measured the elevation of the delta population and compared the obtained dataset with the hypothesized sea level elevation of -2540 ± 177 m firstly suggested by Di Achille and Hynek [1] for a northern ocean through the analysis of deltas.

We observed that, if the relationship between feeding channel length and delta age found for a sub-group of the population [2] is applicable as a rule of thumb to all deltas, many of the deposits have the potential to be Hesperian or Amazonian in age. They would thus be younger than the ocean that might have occupied the northern lowlands during the Noachian-Hesperian boundary period [1] and thus be unrelated to a global sea level range. In fact, less than half of the delta population is related to medium/long feeding channels (>30 km). Abundant pristine morphologies, both related to channels and deltas, also supports the hypothesis that part of the population is younger than Noachian. Additionally, the large variety of elevations where the deltaic deposits can be found and the very small amount of deltas included in the sea level elevation range proposed by Di Achille and Hynek [1] raise questions about the generation and environmental implications of these features, especially when seen at global scale.

[1] Di Achille, G. & Hynek, B. M., Nat. Geosci. 3, 459–463 (2010).

[2] Hauber, E. et al., J. Geophys. Res. E Planets 118, 1529–1544 (2013).

[3] Morgan, A. M., et al., Lunar Planet. Sci. Conf. (2018).

[4] Ori, G.G. et al., J. Geophys. Res. E Planets 105, 17629–17641 (2000).

How to cite: De Toffoli, B., Plesa, A.-C., Hauber, E., and Breuer, D.: Delta Deposits on Mars: A Global Perspective, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5971, https://doi.org/10.5194/egusphere-egu21-5971, 2021.

Introduction:  Martian valley networks are evidence for surface run-off and past water cycles on ancient Mars. Many of the networks resemble terrestrial precipitation-fed systems; however, recent analysis has found that the geometries and morphological characteristics of some valley networks are more comparable to subglacial valley formation. Subglacial valleys have morphological characteristics that make them distinct from fluvial valley systems (i.e., those formed via precipitation or sapping erosion). Unlike fluvial valley networks, which follow the surface slope of the underlying topography, sub-glacial networks are orientated in the direction of the surface slope of the overlying ice-sheet. Therefore, subglacial valleys may have orientations that are discordant with the underlying topography. Discordance analysis, a technique that compares the valley paleoslope direction and topographic slope direction, has been applied to Mars to determine areas that have undergone topographic modification since valley formation. This technique could also be a tool for identify valleys with potential sub-glacial origins.

In this study, we mapped and applied discordance analysis to valley networks in and around Argyre basin. Detailed analysis was performed on four valley networks on eastern Argyre, to determine whether their characteristics are indicative of a fluvial or sub-glacial origin.

Results: 2669 V-Shaped valleys (total length = 36155.5 km) and 45 U-Shaped valleys (total length = 2683.5 km) were identified. Most V-Shaped valleys dissect the eastern and northern rim of Argyre Basin, with fewer in the south and west. The densest northern valley networks have values up to 0.098 km^-1, compared to the densest in the south with values of only 0.040 km^-1. U-Shaped valleys are prominent along the south/south-west rim, but are lacking along the northern rim of Argyre.

Most valleys (47.8 %) are concordant (< 45° discordance) with present slope direction. Two dense groups of discordant valleys are present adjacent to Hale Crater and Nia Vallis. These areas display features associated with the presence of an ice-sheet/glacier – e.g., glacial moraines and eskers. Additionally, the morphology of these valley systems are consistent with a subglacial origin.

Fento Vallis and the Darwin Crater valley system are concordant with present topographic slope, and are in close proximity to one another; however, their morphologies differ greatly. Fento Vallis consists of 25 valleys (total valley length of ~ 690 km) and drainage density of 0.019 km^-1. The Darwin Crater valley network consists of 49 valleys (total valley length of ~ 1351 km) and drainage density of 0.048 km^-1. Fento Vallis displays features (e.g., inner channel eskers) indicative of a subglacial origin. Alternatively, the Darwin Crater System has a planform associated with fluvial activity and originates from cirque like depressions. Although the Darwin Crater system appears to have a fluvial origin, less than 100 km to the east is Pallacopas Vallis, which displays inner eskers indicating that it has a subglacial origin.

Three of the networks analysed, which are > 1000 km apart from one another, are likely subglacial in origin. Their occurrence indicates that an ice-sheet or multiple ice-sheets were present along the eastern region of Argyre throughout its history.

How to cite: Bahia, R., Galofre, A., Covey-Crump, S., Jones, M., and Mitchell, N.: Discordance Mapping of Argyre Basin: An Insight into the Fluvial and Subglacial Origin of Valley Networks in the Argyre Basin Region, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1742, https://doi.org/10.5194/egusphere-egu21-1742, 2021.

We explore the origins of a complex assemblage of sinuous ridges in Chukhung crater (38.47°N, 72.42°W), Tempe Terra, Mars, and discuss the implications of the landsystem for post-Noachian fluvial and glaciofluvial activity in this location [1].

We produced a geomorphic map of Chukhung crater using a basemap of 6 m/pixel Context Camera (CTX) images and a 75 m/pixel High Resolution Stereo Camera digital elevation model (DEM). We used 25 cm/pixel High Resolution Imaging Science Experiment images, and a 24 cm/pixel DEM generated from CTX stereopair images [2] to aid classifications of sinuous ridges into four morpho-stratigraphic subtypes. We constrained an age envelope of ~2.1–3.6 Ga for Chukhung crater using modelled ages (from crater size-frequency analyses) of units above and below it in the regional stratigraphy. We derived a minimum model age of ~330 Ma for viscous flow features (putative debris-covered glaciers) in southern Chukhung crater.

Sinuous ridges in southern Chukhung crater emerge from moraine-like deposits associated with the debris-covered glaciers. Sinuous ridges in northern Chukhung crater extend from dendritic fluvial valley networks on the crater wall. The northern sinuous ridges are most likely to be inverted palaeochannels, which comprise subaerial river sediments exhumed as ridges by erosion of surrounding materials.

Both sinuous ridge subtypes in southern Chukhung crater have numerous esker-like properties. Eskers are ridges of glaciofluvial sediment deposited in meltwater tunnels within or beneath glacial ice. One of the ridge subtypes in southern Chukhung crater is best explained as eskers because these ridges ascend the sides of their host valleys and, in places, escape over them onto adjacent plains. Post-depositional processes can cause inverted paleochannels to cross local undulations in the contemporary topography [3] but the ascent and escape over larger, pre-existing topographic divides is (as yet) not adequately explained by these mechanisms. Eskers, in contrast, form under hydraulic pressure in ice-confined tunnels, and commonly ascend valley walls and cross topographic divides. The esker-like properties of the second sinuous ridge subtype in southern Chukhung crater can also be explained under the inverted palaeochannel hypothesis so the origins of these ridges remain more ambiguous.

Chukhung crater has undergone protracted and/or episodic modification by liquid water since its formation between the early Hesperian and early Amazonian. This falls after the Noachian period (>3.7 Ga), when most major fluvial activity on Mars occurred. Esker-forming wet-based glaciation in Chukhung crater might have occurred as recently as the mid Amazonian (>330 Ma), when climate conditions are thought to have been cold and hyper-arid. Rare occurrences of eskers associated with Amazonian-aged glaciers in Mars’ mid-latitudes are attributed to transient, localised geothermal heating within tectonic rift/graben settings [4]. The location of Chukhung crater between major branches of the large Tempe Fossae volcano-tectonic rift system is consistent with this hypothesis.

References: [1] Butcher et al. 2021, Icarus 357, 114131. [2] Mayer and Kite 2016, Lunar Planet. Sci. Conf. Abstract #1241. [3] Lefort et al. 2012, J. Geophys. Res. Planets 117, E03007. [4] Butcher et al. 2017, J. Geophys. Res. Planets 122, 2445–2468.

How to cite: Butcher, F. E. G., Balme, M. R., Conway, S. J., Gallagher, C., Arnold, N. S., Storrar, R. D., Lewis, S. R., Hagermann, A., and Davis, J. M.: Sinuous Ridges and the History of Fluvial and Glaciofluvial Activity in Chukhung Crater, Tempe Terra, Mars. , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2717, https://doi.org/10.5194/egusphere-egu21-2717, 2021.

Antoniadi basin is a 330 km diameter Noachian basin localized in the East of Arabia Terra that contains a network of ridges with a tree-like organization. Branched ridges, such as these can form by a variety of processes including the inversion of fluvial deposits, thus potentially highlighting aqueous processes of interest for understanding Mars’ climate evolution. Here, we test this hypothesis by analyzing in details data from Colour and Stereo Surface Imaging System (CaSSIS), High Resolution Imaging Science Experiment (HiRISE) and High Resolution Stereo Camera (HRSC).

Branched ridges are up to 10 km long and from 10 to 200 m wide without obvious organization in width. The branched ridges texture is rubbly with the occurrence of blocks up to ~1 m in size and a complete lack of layering. A HiRISE elevation model shows the local slope is of 0.2° toward South, and thus contrary to the apparent network organization (assuming tributary flows). There is no indication of exhumation of these ridges from layers below the current plains surface. Our observations are not consistent with the interpretation of digitate landforms such as inverted channels: (i) The rubbly texture lacking any layering at meter scale is distinct from inverted channels as observed elsewhere on Mars. (ii) Heads of presumed inverted channels display a lobate shape unlike river springs. (iii) There is no increase in width from small branches toward North as expected for channels with increasing discharge rates downstream. (iv) The slope toward South is contrary to the inferred flow direction to the North. The detailed analysis of these branched ridges shows many characteristics difficult to reconcile with inverted channels formed by fluvial channels flowing northward. Subglacial drainages are known to locally flow against topography, but they are rarely dendritic. Assuming that deposition occurred along the current slope, thus from North to South, the organization of the network requires a control by distributary channels rather than tributary ones. Distributary channels are possible for fluvial flows, but generally limited to braiding regimes or deltaic deposits, of which no further evidence is observed here. The lobate digitate shapes of the degree 1 branches are actually more in line with deposits of viscous flows, thus as terminal branches. Such an interpretation is consistent with lava or mudflows that formed along the current topography. The next step in this study will be to determine more precisely the rheology of these unusual flows.

Acknowledgments: French authors are supported by the CNES. The authors wish to thank the spacecraft and instrument engineering teams. CaSSIS is a project of the University of Bern and funded through the Swiss Space Office via ESA’s PRODEX. The instrument hardware development was also supported by the Italian Space Agency (ASI) (agreement no. I/018/12/0), INAF/Astronomical Observatory of Padova, and the Space Research Center (CBK) in Warsaw. Support from SGF (Budapest), the Univ. of Arizona (Lunar and Planet. Lab.) and NASA are gratefully acknowledged.

How to cite: Mangold, N., Tornabene, L., Conway, S., Guimpier, A., Noblet, A., Fawdon, P., Hauber, E., Pommerol, A., and Thomas, N.: Viscous Flows Formed The Branched Ridges Of Antoniadi Crater, Mars, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5946, https://doi.org/10.5194/egusphere-egu21-5946, 2021.

Recurring Slope Lineae (RSL) are dynamic, low-albedo, slope-parallel surface features on Mars that occur mainly on steep (>25°) slopes. RSL typically display seasonal dynamics as they appear during late Martian spring, progressively grow during summer, and subsequently fade as summer ends. RSL formation mechanisms remain under debate with proposed mechanisms involving either water/brines (‘wet theories’) vs. dry granular flows within a surficial dust layer (‘dry theories’). In an attempt to distinguish between plausible RSL mechanisms, this study compares the topographic and morphologic characteristics of hillslopes with and without RSL. We suggest that a distinct topographic signature for RSL hillslopes would argue against the ‘dry’ RSL mechanisms, as RSL dynamics within a thin dust layer are not expected to significantly impact the hillslope-scale topography. In contrast, the presence of fluids on RSL hillslopes could conceivably accelerate rock weathering rates, which in turn may impact the hillslope-scale topography. Our analyses are based on HiRISE, CTX and HRSC digital terrain models (DTMs) together with geomorphic mapping using high-resolution orbital images. We focus on inner crater hillslopes and compare the topographic characteristics of RSL vs. non-RSL slopes. In addition, in order to account for the potential influence of aspect-dependent solar irradiation on hillslope processes, we also applied our analysis on adjacent ‘control’ craters that are devoid of RSL activity. Preliminary results from Palikir (-41.6°/ 202.1°E) and Rauna (35.2°/ 328°E) craters reveal that the topographic slope distribution along crater walls with RSL activity is distinct from the slope distribution along crater walls which are devoid of RSL activity. Our results appear to support increased rock-weathering rates on crater walls that presently experience RSL activity.

How to cite: Adam, A., Haviv, I., Blumberg, D. G., Maman, S., and Mushkin, A.: Do Martian slopes with Recurring Slope Lineae (RSL) have a distinct topographic signature?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6021, https://doi.org/10.5194/egusphere-egu21-6021, 2021.

Polygonal patterned ground is ubiquitous in the martian mid-latitudes and in the polar regions of Earth. The latitude dependence of martian patterned ground and its morphological similarity to terrestrial patterned ground suggests that thermal contraction cracking may have been the leading formation mechanism for those polygons. Due to a lack of ground truthing on martian patterned ground, the role of liquid water in its formation and   weather freeze-thaw processes lead to their origin is still debated. This study uses a quantitative approach, based on geomorphometrical and soil characteristics of patterned ground in continental Antarctica and glacial deposits with low inclination of Terra Nova Bay as terrestrial analogues, to understand polygon formation in martian hyper-arid conditions.  We investigated polygons in ice-free parts of the mountain range of Helliwell Hills (~71°43S / 161°2E) in continental Antarctica and the Northern Foothills in the coastal Terra Nova Bay area (74°45S / 164°E).

Field observations were made during the austral summer on the GANOVEX XI and GANOVEX XIII expeditions in Dec-Jan 2015/2016 and Oct-Nov 2018, respectively. The polygonal troughs have been mapped and digitized in ArcGIS based on high resolution satellite images. For Helliwell Hills we used World View 2 images with a pixel size of 50 cm. For Terra Nova Bay, Quickbird satellite imagery has been used with a pixel size of 60 cm. Based on these datasets, parameters such as area, perimeter, length, and width have been measured, and size, circularity, orientation, and aspect ratio of each polygon were derived from these measurements. Additionally, we used a DTM derived from World View 2 stereo imagery (ground sampling distance: 8 m) to calculate the average slope, aspect, and solar irradiation of each polygon. The quantitative analysis shows that the geomorphometric characteristics of polygons in the Helliwell Hills differ significantly from those in Terra Nova Bay. Polygons in the Helliwell Hills are significantly smaller than in Terra Nova Bay and are organized as orthogonal, random-orthogonal and hexagonal polygon networks, while all polygons in Terra Nova Bay form hexagonal polygon-net geometries. The correlation of polygon-net geometries and the slope gradient shows that hexagonal polygon-net geometries dominate in flat terrains, while orthogonal geometries have developed on steeper slopes or in the immediate proximity of sharp terrain margins such as topographic slopes. The polygons in Helliwell Hills do not display significant local relief, but overall, the polygon centres are slightly higher than the bounding cracks (i.e. high-centered polygons). In Terra Nova Bay the appearance of high centred polygons and a deeper trough is even more developed and well distinguishable on satellite images.

During the fieldwork in Helliwell Hills, excavations were made in the center of polygons and across the bounding cracks. Typically, the uppermost ∼40 cm of regolith are dry and unconsolidated. Below that, there is commonly a sharp transition to ice-cemented material or very clear ice with no bubbles. The grain size analysis indicated no significant trend of sorting. We will present the results of our analysis and compare them with selected polygon sites on Mars.

How to cite: Sassenroth, C., Hauber, E., Baroni, C., Salvatore, M. C., De Vera, J.-P., and Schmitz, N.: Polygonal frost patterned ground as a Mars analogue in Northern Victoria Land, Antarctica, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12265, https://doi.org/10.5194/egusphere-egu21-12265, 2021.

Gully systems on Mars were first reported by Malin and Edgett (Science, 2000) and because of their similarity to gullies on Earth were attributed to the action of liquid water. They are generally kilometre-scale systems where tributary alcoves lead into channel(s), which terminate in digitate deposits and/or fans. They are found on almost all steep slopes polewards of 30°N/S and are oriented towards the pole in the interval 30-40°, then occur on all slope-orientations >40° (e.g. Conway et al. 2019). Their latitudinal distribution and trends in orientation are strong indicators of a climatic factor playing a pivotal role in their formation. Repeat orbital observations have revealed changes in up to 20% of monitored gully systems (Dundas et al. 2019). When the timing of the changes can be constrained, they occur at the end of the seasonal defrosting period when carbon dioxide ice is present at the surface rendering the temperatures too cold for liquid water to be involved (Dundas et al. 2015, 2019; Pasquon et al., 2016, 2019a,b; Raack et al. 2015, 2020). Some changes involve resolvable quantities of sediment, including motion of metre-scale boulders and erosion of new channels (Dundas et al. 2015; de Haas et al. 2019; Pasquon et al., 2019a).

Here, we exploit an exceptional time series to monitor the evolution of gullies and the seasonal frost deposits in Sisyphi Cavi (68-74°S, 345°-5°E). We use image data from HiRISE (High Resolution Imaging Science Experiment; 0.25-1 m/pixel), CaSSIS (Colour and Stereo Surface Imaging System; 4.5 m/pixel) and CTX (Context; 6 m/pixel). CaSSIS has four colour filters: BLU, PAN, RED and NIR (centred on 500, 675, 836 and 937 nm respectively); where the BLU filter is particularly useful for picking up surface frosts (Tornabene et al. 2019). We find that gullies and dunes are the last surfaces to defrost in the area. Independent of slope-orientation the alcoves of the gullies defrost first, followed by their channels then their fans. A surprising result considering that intuitively defrosting should progress from the equator-facing alcoves to the equator-facing fans, then from the pole-facing fans to the pole-facing alcoves. We infer that this is a consequence of a) fans and alcoves having contrasting thermal inertia and b) alcoves having slope-facets with a range of local orientations (with some proportion being equator-facing independent of overall orientation).

We observe dark spots, dark flows and dark fans at the metre-to-ten-metre-scale. These features occur when a continuous solid slab of translucent CO2-ice is penetrated and warmed by sunlight at its base. The sublimation drives gas build-up under the slab, ruptures it, entraining dust and then depositing the dust on the surface (e.g. Kieffer et al. 2006) to form spots, flows and/or fans, depending on the context. We find that the recent activity of gullies promotes the formation of dark spots/flows/fans and are investigating the inverse relationship.

Acknowledgement: CaSSIS is a project of the University of Bern, with instrument hardware development supported by INAF/Astronomical Observatory of Padova (ASI-INAF agreement n.2020-17-HH.0), and the Space Research Center (CBK) in Warsaw.

How to cite: Conway, S. J., Pasquon, K., Lewis, S. R., Vincendon, M., Massé, M., Raack, J., Noblet, A., and Philippe, M. and the CaSSIS Team: The seasonal evolution of ices on the gullied slopes of Sisyphi Cavi on Mars using CaSSIS and HiRISE orbital images, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8812, https://doi.org/10.5194/egusphere-egu21-8812, 2021.

The presence of volcanism is often anecdotally used to define a “living planet”. Since dome-building volcanism on Earth occurs primarily at plate boundaries, the identification of such domes could inform on exoplanetary development. Lava domes form when extruded magma is too viscous to flow from a vent, and their morphology on Earth varies from flat, pancake lobes to steep, blocky domes. Identification of lava domes on other terrestrial planets in our Solar System indicates that they likely also exist on rocky exoplanets. Here we show, using particle-based modelling, that the diversity of lava dome morphology in our Solar System is dwarfed by the diversity expected for exoplanets. Specifically, the height-to-diameter ratio of a dome decreases as a function of increasing gravity (i.e., planetary mass and radius). For example, lava domes on high-gravity super-Earths will be extremely wide and flat and a volcanic origin may not be immediately apparent. Creating a toolbox to help identify exoplanetary volcanism will allow us to make initial estimations as to the development and habitability of these alien worlds as images become available.

How to cite: Harnett, C., Heap, M., and Thomas, M.: A numerical modelling toolbox for identifying the expression of dome-forming volcanism on exoplanets, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9482, https://doi.org/10.5194/egusphere-egu21-9482, 2021.

Compared to Earth, the surface erosion activity of Mars is low, so Martian landscapes can survive for  long time, therefore Martian surface has been observed and analysed since the earliest times of Mars research. Because the planet’s geological and mass wasting history can be studied with remote sensing, observations may provide deeper insight into the early evolution of the planet (Golombek & Bridges, 2000). Lack of precipitation, vegetation and human influence have preserved landforms of Mars that have disappeared on Earth. Yet, local sampling and analysis of rocks are not possible, the evaluation of DTM data can deliver information. Presumably all the terrestrial geological processes also took place on Mars, therefore comparative observations provide a great opportunity to study landforms similar to terrestrial features. The most important difference between terrestrial and Martian surface processes is the formation of impact craters; but volcanic processes create specific volcanic edifices too. Of course, due to the different gravity forces and the lack of some surface effects, larger volcanic forms can also be found than on Earth.

We focus on the less researched smaller volcanic edifices. The morphometric studies on terrestrial scoria cones have revealed interesting details (Wood 1979; Brož et al., 2015): properties often can be related to their chronology. This pilot project intends to gather similar knowledge on smaller Martian volcanoes. With the development of morphometric technology, we may get an increasingly accurate picture of the surface and geology of Mars (Mars Trek). Besides the description of the physical appearance of the edifices, parameter extraction may lead to their classification or grouping. These studies may pave the way characterisation of Martian cones.

Previously we have examined the morphometry of several terrestrial scoria cone areas; a relatively simple structure were chosen to reduce the number of the geomorphometric parameters. In this project we apply the same simplification: the varying resolution of DTMs, the lack of proper geological maps limit the evaluation to the simple parametrisation. Furthermore, the sizes and characteristic slopes are different, but the results are promising. The automated parameter extraction seems to be suitable for processing multiple and large number of terrain data. This is a work in progress towards an extensive geomorphometric evaluation of Martian scoria cones as well.

F.V. was supported by the ÚNKP-20-3 New National Excellence Program of the Ministry for Innovation and Technology from the source of the National Research, Development and Innovation Fund.

Brož, P., Čadek, O., Hauber, E., & Rossi, A. P. (2015). Scoria cones on Mars: Detailed investigation of morphometry based on high-resolution digital elevation models. Journal of Geophysical Research:  Planets, 120(9), 1512-1527.

Golombek, M. P., & Bridges, N. T. (2000). Erosion rates on Mars and implications for climate change: Constraints from the pathfinder landing site. Journal of Geophysical Research: Planets, 105(E1), 1 841- 1 853.

Mars trek. (n.d.). NASA Solar System Treks. https://trek.nasa.gov/mars/

Wood, C. A. (1979). Monogenetic volcanoes of the terrestrial planets. Proceedings of the Tenth Lunar and Planetary Science Conference, 2815-2840.

How to cite: Vörös, F. and Székely, B.: Geomorphometric study of Martian scoria cones, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11392, https://doi.org/10.5194/egusphere-egu21-11392, 2021.

Impact craters are often used to date planetary surfaces, the density of crater increasing with the exposure age of the surface. However, some geologic event, such as lava flows, do not totally “reset” the crater clock. Indeed, larger craters, rather than being totally recovered by the lava flow will be only partially filled.

In that case, the crater size frequency distribution differs from cratering models. In order to better describe crater populations, additional parameters can be included. To this purpose we build crater size and depth frequency distributions that offers a snapshot of the current degradation state of the population.

We used cratering models to interpret crater size and depth frequency distributions in terms of crater infilling rates. Using both global crater database and more local high resolution crater maps, we estimated crater obliteration rates on various Martian volcanic provinces.

Our method proven efficient to track activity of the main Martian volcanic provinces. Resurfacing rates reach several thousands of m/Gy. Pic activity differs from provinces. Syrtis and Hesperia are the oldest with the highest and oldest observed rates around 3.7 Gy. The activity of those provinces quickly decreases reaching few hundreds of m/Gy around 3.4 Gy. During Hesperian, Tharsis is the most active surface of Mars with high resurfacing until 3.3 Gy. Finally, our result shows an increase of resurfacing, reaching few hundreds of m/Gy in Amazonis planitia from 2 Gy to present.

How to cite: Breton, S., Pan, L., Quantin-Nataf, C., Brustel, C., and Flahaut, J.: Tracing Martian volcanic activity using crater obliteration rate, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11520, https://doi.org/10.5194/egusphere-egu21-11520, 2021.

The Andean volcanoes in the Atacama Desert offer a unique environment to perform remote sensing investigations as these bare surfaces are well exposed and well preserved due to their relatively young (quaternary) ages, and to hyper-arid environmental conditions. The Atacama Desert is, in fact, the driest non-polar desert on Earth, and for this reason, it has already been previously studied as a Moon and Mars analog environment (e.g., Flahaut et al., 2017). In the present study, we compare dacitic domes from the Altiplano-Puna Volcanic Complex (APVC) of the Atacama desert with volcanic edifices which have been previously reported as possible silicic domes on the Moon.

Five Atacama domes were studied from orbit, and three of them were sampled to obtain ground truth. These features formed by monogenetic eruptions and comprise high-K dacitic to rhyodacitic compositions with SiO₂ contents ranging from 66 to 68 wt%. The dome dimensions measured from ASTER DEM indicate diameters between 1.5 to 6.2 km and heights between 250 and 700 m. Similar measurements were performed on various lunar domes with the LOLA DEM and show diameters ranging from a few km to 30 km, with slopes up to 9°. To the first order, dome eruptions can be considered as the extrusion of a Bingham fluid (the cooling magma) characterized by a yield strength τ and a plastic viscosity η (e.g., Hulme, 1974). Using the dome 3D dimensions as inputs into a rheological model, we estimate apparent viscosity to be in the order of 10⁹-10¹¹ Pa.s for both the Atacama domes and the lunar silicic domes.

In parallel, the non-Arrhenian Newton silicate melt viscosity is calculated using the Atacama dome bulk composition and the model of Giordano et al. (2008). Resulting liquid viscosities range from 4.5 to 8 x 10⁶ Pa.s. The difference between the apparent and actual liquid viscosity was further used to calculate the packing fraction with the Einstein-Roscoe equation, which was found to be around 0.70-0.73 for all domes.

Dacitic domes in the APVC have aspect ratios, yield strengths and apparent viscosities similar to the Gruithuisen and Mairan lunar edifices, where elevated silica contents were previously reported (Glotch et al., 2011). We thus argue that the studied domes may be good analogs for these lunar domes, which are likely made of felsic rocks. However, when comparing viscosity estimates obtained from remote sensing data (apparent viscosity) and sample analyses (liquid viscosity) for the domes, we found that they differ by several orders of magnitude. Plausible explanations, which include a high amount of crystals in the mush (suggested by the high packing fraction values) will be discussed at the conference time.

References:  Flahaut J. et al. (2017), Icarus, 282, 152-173; Giordano D. et al. (2008), EPSL 271,123–134; Glotch, T. D. et al. (2011), GRL, 38, L21204; Hulme G. (1974), Geophys. Journal International, 39 (2), 361–383.

How to cite: Flahaut, J., González-Maurel, O., Godoy, B., Martinot, M., and Guitreau, M.: Rheology of the Andean domes as an analog for lunar silicic constructs, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11780, https://doi.org/10.5194/egusphere-egu21-11780, 2021.

The Nullarbor Plain is ~200,000 km² large planar karst surface in southern Australia, composed of middle Cenozoic shallow-water limestones of Eucla Group. The youngest formation, covering the top of the plain, is middle Miocene extremely fossiliferous sub-tropical Nullarbor Limestone. In the late Middle Miocene the area was uplifted and exposed to terrestrial denudation and erosion since. Although the plain is in general considered extremely flat, the present geomorphological features indicate a relatively complex geomorphology formed by a combination of tectonic deformation, fluvial and aeolian activity and karst denudation. Due to the absence of orogenesis and only minor influence of post-Miocene sediment deposition, the geomorphology of the Nullarbor preserved footprints of Earth processes through a long, middle Miocene-to-present, time span.

The presence of dry climate and consequent lack of vegetation also aided for numerous meteorite findings, but no visible impact deformations have been recorded. The latter, in combination with capability of the plain to inherit/imprint old geomorphological features, and accessibility of recently built 0.4 arc sec TanDEM-X-DEM by the German Aerospace Centre, motivated the search of a possible meteorite craters with spatial analysis of the plain. The analysis of DEM images revealed a single geomorphological feature with circular uplifted rim (diameter: 1200 m – 1300 m; height: 7 m in relation to outer elevation; width: 200 – 450 m), central uplift (diameter: 500 m; height: 10 m in relation to outer elevation), and a circular trough in between (2 – 3 m higher than outer elevation). Its morphology differs from other geomorphological features observable on the Nullarbor Plain, and represents a unique phenomenon, which cannot be explained as a part of tectonic, volcanic, fluvial, karst or aeolian processes.

This feature is therefore a candidate for a possible relict of a meteorite crater, which occurrence is supported by topographical characteristics including uniqueness of the shape compared to other features on the plain. On the other hand, geological characteristics of the exposed rock within the “crater” lack any of the general diagnostic evidence for impact events (e.g., shocked quartz, brecciation), but rather indicate presence of boundstones with frame-builders preserved in in-situ position and thus suggesting the preservation of a bioherm. The occurrences of bioherms, however, are seldom individual (unlike impact craters) and more likely occur in clusters. The question remaining for this conference discussion is whether dissolutional imprinting of an impact crater could denude any of the characteristic impact structures whilst preserving the shape, or are we looking at a single bioherm preserved as a primary marine depositional feature?

ACKNOWLEDGEMENT: We acknowledge the financial support of Slovenian Research Agency (P6-0101; I0-0031; N1-0162), the Australian Speleological Federation Karst Conservation Fund and TerraSAR-X / TanDEM-X (DEM_GEOL2288).

How to cite: Lipar, M., Ferk, M., and Šmuc, A.: Impact crater versus bioherm on the Nullarbor Plain, Australia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7609, https://doi.org/10.5194/egusphere-egu21-7609, 2021.

The Close-UP Imager (CLUPI) is one of the instruments of the Rosalind Franklin rover, which will explore Mars in the framework of the ESA/Roscosmos ExoMars mission. CLUPI will be mostly used for acquiring close up-images of geological samples, identifying materials and sedimentary structures that may record information about the hypothetical existence of past extraterrestrial life. Although the technical specifications of CLUPI are well known, it is not possible to readily translate such specifications in terms of feasibility to recognize “textures of interest” at a given distance under specific light conditions on Mars. Accurate predictions are important for taking informed decisions during the tactical planning of the rover. Here, we describe the results of some mission-preparation activities, during which a camera system analogue to CLUPI has been used to photograph rocks samples in an indoor facility (i.e., the Marslabor of the University of Basel) that has been built for simulating a Martian landscape. Under different light conditions, we performed a preliminary assessment of the minimal-working-distance required for interpreting rock textures and sedimentary structures that are potentially present on Mars, including textures that allows for differentiating sedimentary rocks from igneous rocks, grains that allows for classifying sedimentary rocks based on their granulometry, and stromatolitic laminations representing morphological biosignatures. The produced data represents a first step in identifying ideal CLUPI working-distances and illumination, and in preparing an image database that will be of help for optimizing rover operations and the scientific return of  CLUPI during the ExoMars 2022 mission.

How to cite: Bontognali, T., Meister, Y., Kuhn, B., Josset, J.-L., Hofmann, B., and Kuhn, N.: The Marslabor of the University of Basel: Simulation of CLUPI operations in view of the ExoMars 2022 mission, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11706, https://doi.org/10.5194/egusphere-egu21-11706, 2021.