GM11.1

The surface of Ganymede, the largest satellite of Jupiter, consists of a strongly deformed and tectonized  brittle icy crust which stands on top of a large liquid body, possibly a global subsurface ocean. In fact, by means of multiple Galileo orbital mission flybys both geophysical and structural geology measurements constrained the average icy shell thickness to be comprised between 100 and 150 km. The surface can also be divided into two main units: bright and dark terrains depending on their relative albedo, impact crated density and tectonization. Furrows and grooves represent most of the structures on Ganymede’s surface, which are essentially extensional faults, dilatant structures and strike slip faults. We hereby present a 3D geologic modelling of the region of Uruk Sulcus based on structural mapping (Rossi et al., 2020) and using techniques borrowed from oil and gas exploration.

The Uruk Sulcus area is a NW-SE bright terrain of  ~400 km by ~2500 km size located between 150W-180W and 30N-10S, and characterized by pervasive sets of parallel/sub-parallel grooves of 10s-to-100s km length. The most favored hypotheses relate its formation either to a purely extensional context forming a tilt-block normal faulting, or to crustal necking with creation of horsts and grabens, or to be the result of a major dextral transpression. The overall structural framework and the fault geometries (in the form of 3D meshes) was created according to existing literature and with geologic interpretation and anchored on the surface to the global DEM by Zubarev et al., (2017), and at depth to the brittle ice-subsurface ocean interface to an average value of 120 km. This ice thickness value was obtained, among other methods, also by analyzing the scaling laws ruling the spatial distribution and the length size distribution of grooves and extensional structures, which proved to be fractal. One of the implications of this fractal behavior is that the structures themselves can be interconnected forming a percolating network favoring fluid circulation and connecting the subsurface ocean with the surface (see Lucchetti et al., 2020 and references therein).

By means of 3D modelling, we were able to isolate volumes of ice encompassed by major strike-slip structures of Uruk Sulcus and to exploit the scaling laws ruling the structures within such areas, in order to numerically simulate a DFN (digital fracture network) crosscutting the entire volume of ice.

This way we could analyze the volume of ice crosscut by such fracture network, and to predict the locations at surface where percolation is favored.

Acknowledgments: The activity has been realized under the ASI-INAF contract 2018-25-HH.0.

How to cite: Pozzobon, R., Rossi, C., Lucchetti, A., Massironi, M., Pajola, M., Penasa, L., and Munaretto, G.: 3D geologic model of Uruk Sulcus region on Ganymede, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11526, https://doi.org/10.5194/egusphere-egu22-11526, 2022.

The smallest of Jupiter’s Galilean satellites, Europa has one of the smoothest surfaces of our solar system. This is due to the comparative youth of its ice crust which is believed to resurface over time. This ice crust is observed to be crisscrossed with a multitude of linae, thought to be large-scale fractures, as well as dotted with numerous regions of lenticulae and chaos. Tidal stresses on Europa are modelled according to Wahr (2009) and are evaluated over periods of 1e3-1e6 years. The nucleation, growth and interaction of fractures is modelled using a three-dimensional finite element-based fracture simulator which assumes that the material is linear, isotropic and homogeneous. Other material properties are drawn from Selvans (2009). Nucleation of fractures is assumed to occur only in tension, and sub-scale nucleation modelled by a damage criterion models the weakening of the ice matrix. Stress intensity factors at the fracture tips are computed with the displacement correlation method. Fracture growth is modelled geometrically as a function of the accumulation of stresses on the fracture tips. The simulator evaluates how tidal stresses are expected to induce the nucleation and growth of fractures on the surface of Europa. Nucleation and growth are modelled in two regions, an equatorial region and a sub-polar region, representative of deformation scenarios on the satellite surface. The simulation runs at two different scales. Tidal forces are computed at the satellite scale using Wahr (2009). These are applied as boundary conditions of smaller scale 100km x 100km x 20km cuboidal regions, in which the nucleation and growth of fractures is modelled. Within each region, a number of three dimensional non-planar fractures grow and interact. Resulting patterns are compared against observational data.

How to cite: Walding, J. and Paluszny, A.: Multi-scale modelling of ice fracture patterns on the surface of Europa using computationally derived tidal boundary conditions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7737, https://doi.org/10.5194/egusphere-egu22-7737, 2022.

The surface of Ganymede, which is the biggest satellite of Jupiter, shows strong tectonic deformation affecting both its geologic units, i.e., the younger light terrain and the older dark terrain. The dark terrain is characterized by low albedo, high crater density and furrows, which are morphotectonic structures formed by brittle deformation. Furrows are straight to curved fragments of troughs, with high albedo rims that bound a low albedo floor. Two systems have been recognized at the regional scale, which are the Lakhmu Fossae, whose furrow setting follows a concentric pattern resulting from a multi-ring impact basin, and the Zu Fossae, which follows a radial setting. In addition, local scale structures have been identified superimposed on the regional scale systems, leading to the reworking of the pristine structures. In this contribution, we investigate the tectonic evolution of the furrows in Galileo Regio (approximately from 180°-120° W to 0°-60° N), at both regional and local scale, with the identification of the tectonic events responsible for the deformation of this dark terrain. We performed a structural mapping and geostatistical analyses of the attributes of the mapped structures, such as the length, sinuosity, azimuth, spacing within the adjacent structures. Their quantification allows us to recognize a total of four structural systems within the area and to unravel the paleo-stress fields that have originated them. We prepared an evolutionary tectonic model of the furrow systems of Galileo Regio that shows the dynamics and the induced kinematics. We suggest that Galileo Regio underwent a sequence of tectonic phases associated with extensional and strike-slip regimes, these latter consistent with the kinematics that affected the light terrain of the adjacent Uruk Sulcus. This work advances the assumption that the dark terrain has been later affected by the same tectonics that deformed the light terrain and confirms the rejuvenation of the dark terrain towards a possible future transformation into light ones. The obtained results will be used for the scientific preparation of dedicated high-resolution observations that will be taken with the JANUS instrument onboard JUICE mission.
Acknowledgments: The activity has been realized under the ASI-INAF contract 2018-25-HH.0.

How to cite: Rossi, C., Lucchetti, A., Massironi, M., Pozzobon, R., Penasa, L., Munaretto, G., and Pajola, M.: Tectonic phases in Galileo Regio, Ganymede’s dark terrain., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10095, https://doi.org/10.5194/egusphere-egu22-10095, 2022.

The area on the eastern slopes of Tharsis (Thaumasia), northern from Argyre and southern from Margaritifer is dominated by the Uzboi Vallis and Nirgal Vallis. Their (at least partial) fluvial origin is accepted since the Mariner-Viking era. Uzboi Vallis thought to be part of the ancient Uzboi–Ladon–Morava River System (ULM). ULM is thought to be created while it served as the overflow channel of the southern Argyre crater. Nirgal Vallis is the largest tributary of Uzboi. Its source region is in the direction of the Thaumasia Mountains.

The area experienced numerous effects during its history. In this study our goal was to separate these effects in a chronological order as far as it is possible. Therefore comprehensive investigations (using MOLA and THEMIS) were carried out and a detailed analysis of these two valleys was made using HiRISE images and HiRISE-derived digital elevation models. HiRISE DEMs allow the surfaces to be studied and evaluated with a resolution of better than one meter.

Several geomorphometric methods were applied for the area: swath analysis, the distribution of the tributary valleys, sinuosity calculation, and runoff modeling. The vallis was divided into sections based on its main features. Section A, unlike other sections, is characterized by dendritic tributary system. Tributaries are found both on left and right sides. Section B is a kind of transitional zone, the tributaries are getting rare. Section C was defined as a sinuous segment. Tributaries here are very rare.  Section D is deeply incised, the thalweg is broken at several points and has a subhorizontal trend. According to the extremely low number of tributaries and the modifying effect of the neighboring impact craters the water divides are fuzzy. The path of this section is also sinuous. Section E is the deepest part of the whole Nirgal Vallis this is an unusual condition, because in the case of the terrestrial rivers the deepest part is regularly at the end of the confluence. Section F has to be separated from Section E because it shows influence of several effects. Section F has got only one (SW-NE) tributary which is significant in length and dominates the morphology of the area south from the Nirgal‒Uzboi confluence.

In our interpretation the sections detailed above seem to be at least partially related to wrinkle ridges noticeable from Thaumasia Mountains to Uzboi Vallis and are similar to those on Solis Planum. The effect of the wrinkle ridges is controlling the morphology of the plateau, and may be in connection with the tributaries.

Further geomorphological investigation may lead to the separation of the different effects formed Nirgal throughout its history.

How to cite: Szilágyi-Sándor, A. and Székely, B.: Geomorphometric Analysis of the Martian Uzboi-Nirgal Region, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8488, https://doi.org/10.5194/egusphere-egu22-8488, 2022.

Forming spontaneously when sediment laden water flows across an erodible material, terrestrial river channels possess a distinct shape, with robust relationships between channel width, depth and flow velocity that hold true over a million-fold change in water flux and for widths spanning less than a meter to more than a kilometer. These patterns have long since been described, however, a process-based understanding of what determines channel shape and scale is just beginning to emerge. This recent work has made clear the key elements to understanding terrestrial river channels which include: lateral momentum exchange within the flow, the frictional behavior of the channel boundary on the flow, and the dynamics of bedload sediment transport in the channel.  Bringing together these elements, a theoretical prediction for steady-state channel shape is derived directly from the Navier-Stokes equations of motion. 

The key result is an analytical description of channel geometry relating seven variables: flow width, depth, velocity, channel slope, and characteristic grain size, water flux and sediment flux. Using these equations, any four variables can be predicted if the other three are known. The theory was tested against 2500 terrestrial river reaches including both bedrock and alluvial rivers, where width varies by three orders of magnitude, and characteristic water flux varies by seven orders of magnitude. Using characteristic water flux, characteristic grain size, and a global average sediment transport rate, flow width, depth and velocity are predicted to within a factor of two for >80% of reaches.  

There are other long-lived geophysical and extraterrestrial flows over erodible materials that can be addressed with a general understanding of self-formed channels. With estimates of how fluid drag, turbulence generation and sediment transport might change on other planetary bodies, this model could be applied to extraterrestrial river networks such as those observed on Mars or Titan. More fundamentally, this work suggests a general approach to understand self-formed channels in an erodible medium generated by different kinds of flow, such as valley glaciers and subglacial river channels on both Earth and Mars. 

How to cite: Deal, E.: A mechanistic understanding of self-formed channel shape and scale, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7147, https://doi.org/10.5194/egusphere-egu22-7147, 2022.

Fluvial fans and river deltas are both fan-shaped landforms that contain complex channel networks. A critical difference between these landforms is that deltas form only along a standing body of water, whereas fluvial fans may form hundreds of kilometers from oceans or lakes. Accurately distinguishing between deltas and fluvial fans is thus critical for identifying paleo-shorelines on planetary bodies. Here we test an ensemble of quantitative methods to differentiate fluvial fans and deltas on Earth, and apply the methodology to Mars. We quantify differences in channel divergence angles, and in downstream changes of channel reach lengths and channel width between the divergence nodes. These differences in channel networks occur because fluvial fans build by channel avulsions, whereas delta build by avulsions as well as mouth bar growth and consequent bifurcations. Bifurcations in deltas form channel divergence angles of approximately 77° and cause a distinct downstream decrease in channel reach length and in channel width at bifurcation nodes. In contrast, avulsions in fluvial fans form considerably smaller channel divergence angles. Down-fan channel narrowing is also not linked to divergence nodes. This initial dataset shows that the methodology is applicable both on Earth and Mars, and that the Jezero system is likely a fluvial fan rather than a delta. These results indicate that channel networks need to be carefully assessed if used for the estimation of the location of paleo-shorelines on planetary bodies, as only deltas systematically occur at shorelines. Alternatively, additional evidence is needed for the presence of shorelines as fluvial fans may also occur at shorelines. On Earth, fluvial fans are less sensitive to sea-level rise and coastal hazards than deltas, due to upstream morphodynamic controls.

How to cite: Gezovich, L., Plink-Bjorklund, P., and Henry, J.: Morphometric analysis of channel networks suggests the Jezero system is a fluvial fan rather than a delta, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10768, https://doi.org/10.5194/egusphere-egu22-10768, 2022.

Introduction:  Mars’ surface is carved by an array of dendritic valley networks, which are evidence for ancient water cycles and surface run-off on Mars. The majority of these networks appear to have formed during the Late Noachian – Early Hesperian (3.8 to 3.6 Ga) and resemble terrestrial precipitation-fed systems. After this period, other than localised valleys present on the flanks of several volcanoes, valley network formation appears to have rapidly decreased, indicating that Mars’ climate experienced a sudden change from a warm and wet state to hyper aridity. However, a recent analysis of Amazonian – Hesperian aged flat crater-bottom deposits and alluvial fans indicates that localised areas of wettest persisted after the Early Hesperian. By analysing the morphological, morphometric, and paleohydraulic characteristics, and formation timescales of valley networks of different ages, one can gain a better understanding of the evolution of Mars’ aridity.

In this study, we aim to perform a detailed analysis of valley networks of differing ages to determine their formation origin and the duration of aqueous activity required to incise their troughs. At present we have performed formation timescale analysis on an Amazonian-Hesperian aged valley network – the results are presented below.

Data and Methods: A combination of GIS software packages were used to perform the analysis: SAGA GIS was used to determine full water depth estimates and flow width via the multiply flow direction method; GRASS GIS was used to determine flow accumulation, flow direction, and upstream slope; ArcGIS Pro was used to perform spatially variable drainage area calculations for Hack’s Law and Flint’s Law calculations. Valley networks were initially identified using the Hynek et al. (2010) valley map, and narrowed to different surface ages based on the Tanaka et al. (2014) surface age map. Detailed mapping and morphological analyses of these valleys was performed using Context Camera images (5 m per pixel). High-Resolution Stereo Camera (HRSC) DEMs were used for paleohydraulic and formation timescale analysis. For the formation timescale calculation, the estimated volume (km³) of each pixel was divided by the volumetric transport rate (km³/yr).

Initial Results: At present, we have applied the technique to a valley network located north-east of Lowell Crater (49.82 °S 77.16 °W). The source is within a Middle Noachian highland unit, with the majority of the network incising an Amazonian-Hesperian aged impact unit. The valley network has a main valley length of ~123 km, an almost linear profile, and an average slope (dz/dl) of ~ 0.012. Based on a calculated average water velocity of 6.8 m/s and an average 12.25 m water depth, the average formation time for the whole study area is 23235.3 yr (1 sigma standard deviation = 39401.2 yr).

Discussion: It is apparent the examined young valley is immature compared to previously examined Late Noachian – Early Hesperian Martian valley networks, which have minimum formation timescales ranging from 10⁵ to 10⁷ years. Applying formation timescale and paleohydraulic calculations to valley networks from a range of ages, we will be able to better understand the evolution of fluvial activity that formed them.

How to cite: Bahia, R. and Steinmann, V.: The Evolution of Martian Valley Network Formation Timescales, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1282, https://doi.org/10.5194/egusphere-egu22-1282, 2022.

The lack of evidence for large-scale glacial erosion on Mars has led to the belief that any ice sheet that may have existed had to be frozen to the ground. We challenge this argument, suggesting instead that the fingerprints of Martian warm-based ice masses should be the remnants of their drainage systems, including channel networks and eskers, instead of the large scoured fields generally associated with terrestrial Quaternary glaciation. Our results use the terrestrial glacial hydrology framework to interrogate how the Martian lower surface gravity should affect the state and evolution of the glacial drainage system, ice sliding velocity, and the rates of glacial erosion. Taking as reference the scale and characteristics of the ancient southern circumpolar ice sheet that deposited the Dorsa Argentea formation, we compare the theoretical behavior of geometrically identical ice sheets on Mars and Earth and show that, whereas on Earth glacial drainage is predominantly inefficient, enhancing ice sliding and producing characteristically scoured glacial landscapes, on Mars the lower gravity favors the formation of efficient subglacial channelized drainage. The apparent lack of large-scale glacial fingerprints on Mars, such as scouring marks, drumlins, lineations, etc., is thus to be expected. 

How to cite: Grau Galofre, A., Whipple, K., and Christensen, P.: The (missing) erosional record of warm-based glaciation on early Mars, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4749, https://doi.org/10.5194/egusphere-egu22-4749, 2022.

The fluid dynamics of different sedimentological processes are often studied and interpreted by using models based on a combination of Newton dynamics and an empirical expression of the drag force in function of the drag coefficient. However, neither the expression of the drag force nor the value of the drag have a unique expression, depending on the state of the fluid (laminar, transitional, and turbulent) and on the shape and dimensions of the sediments. These (semi-) empirical models are often inaccurate, in particular in planetary sciences when gravity plays a determining role, like, for example, when calculating the terminal settling velocity of natural sediments on Mars. In this work, a numerical simulation code based on the Lattice Boltzmann Method (LBM) is used to study how settling velocity of some reference spherical particles changes at different gravity conditions, ranging from hyper to reduced gravity. LBM is a discrete computational method based on the kinetic Boltzmann equation that describes the dynamics of a fluid on a mesoscopic scale. This study shows that, despite the LB model has been calibrated and validated using only the set of experimental data collected during a parabolic flight, its validity goes beyond, being able to predict the correct terminal velocity of different particles, with different density and diameters. In addition, the same settings can be used to simulate other important processes that occur when sediments interact with each other and the fluid phase, such as hindered settling and the drafting, kissing, and tumbling phenomenon. This makes the Lattice Boltzmann method an ideal candidate for studying a wide range of sedimentological processes where a mesoscale accurate description is crucial to understand macroscale phenomena.

How to cite: Trudu, F., Vancheri, A., and Kuhn, N. J.: The Lattice Boltzmann Method: one single tool to address different sedimentation processes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6131, https://doi.org/10.5194/egusphere-egu22-6131, 2022.

Until recently, sand dunes on Mars were thought to be relict landforms from paleo-atmospheric conditions. However, recent evidence from high resolution imagery of Mars’ surface have shown that aeolian processes are a dominant, contemporary force, driving geomorphological change in dune fields across the planet. Images from the HiRISE camera have demonstrated that not only are dune fields active on Mars, but they are undergoing change comparable to some terrestrial rates.

In the absence of localised in situ wind data returned by successive lander missions, the atmospheric-surface interactions contributing to aeolian change across the surface of Mars have largely relied on mesoscale modelling, these large-scale models have not fully resolved the processes occurring at local landform scales. In order to attempt to resolve the interactions driving the modification of dune fields, microscale wind flow modelling (<2 m grid spacing) is required over a site which has been shown to undergo change over the history of HiRISE imagery.

A large barchan dune field in the Nili Patera caldera was selected for examination, as this site undergoes significant aeolian change. This site has a robust HiRISE image collection, but no in situ data, and is therefore an ideal location to test a new multiscale airflow modelling approach. This study proposes combining macro- (>100 km), meso- (>2 km) and microscale (>2 m) modelling of the Martian atmosphere.

The resolution of a Global Climate Model (GCM) is too coarse to resolve the near-surface processes themselves, but their output can be used to provide an initial state and boundary conditions for mesoscale modelling. However, the maximum resolution of a typical mesoscale model is still too coarse to resolve the microscale dynamics contributing to aeolian change at dune fields on Mars. To examine the fine-scale interactions occurring over the surface of dune fields, microscale Computational Fluid Dynamics (CFD) simulations utilising the mesoscale model output are required.

The surface shear stress output from the CFD simulations and corresponding flux predictions were directly compared to HiRISE observations of Nili Patera, using COSI-Corr software to verify the microscale modelling results. We find that this multi-scale modelling approach provides promising initial comparisons between CFD simulations and HiRISE observations, both in the directionality of dune change and the rates of sediment flux, and different Mars seasons., however these observations are influenced by the seasonal variability on Mars, altering approach directions and wind speeds to produce heterogeneous patterns of aeolian flux.

How to cite: Love, R., Jackson, D., Michaels, T., Smyth, T., Avouac, J.-P., and Cooper, A.: Measured and predicted aeolian flux at Nili Patera, Mars: Computational Fluid Dynamics-derived transport modelling and Cosi-CORR rates, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9315, https://doi.org/10.5194/egusphere-egu22-9315, 2022.

Landslides are almost ubiquitous in the Solar System, with rockfall and avalanches that are observed also on other terrestrial bodies, such as the Moon (Bart, 2007; Xiao et al., 2013), Mars (Crosta et al., 2018; Lucchitta, 1987) and Mercury (Malin & Dzurisin, 1978). Landslides and mass movements have been observed also on planetary bodies characterized by extremely low gravity, as for example asteroids’ surfaces of Vesta and Ceres (Otto et al., 2013; Schmidt et al., 2017). The behaviour of mass movements on these bodies is poorly studied due to the difficulties of recreating low-gravity experimental conditions or identifying satisfactory analogues for the involved materials. In fact, the overall dimensions and morphology of the resulting deposits (area, width and length) are often the only features that can be studied and compared between different sites or planetary bodies, due to the limitations in DEMs resolution and suitable imagery.  In particular, plots of the H/L ratio (drop height/runout length) provide a proxy for the average friction coefficient and have been the subject of many comparative investigations.

With the aim of providing a more consistent picture of the possible outcomes of landslides and other mass movements we hereby describe a fully parametric numerical framework based on ESyS-Particle software  (Abe et al., 2004; Tancredi et al., 2012), which has been specifically designed to explore the outcomes of fragmenting grain flow under different model assumptions. The framework has been designed to leverage modern distributed computing technologies to increase the number of simulations that can be executed in parallel, and to maximize the usage of already-available computing hardware. Preliminary results and the limitations are also presented and discussed.

This framework will support the parametrization of numerical models for the upcoming observations of mass-movements of the future JUICE-JANUS camera observations on Jupiter Icy Moons.

Acknowledgements: The activity has been realized under the ASI-INAF contract 2018-25-HH.0.

How to cite: Penasa, L., Lucchetti, A., Pozzobon, R., Munaretto, G., Pajola, M., and Rossi, C.: A Discrete Elements Modelling Framework for the Parametric Study of Landslides in Low Gravity Environments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11400, https://doi.org/10.5194/egusphere-egu22-11400, 2022.