Displays

Active glacial environments exhibit characteristic landforms due to the interplay of ice, climate, soil, and rock. These landforms are used as indicators of past and present climate conditions, and the base of knowledge established by studying glacial morphologies on Earth has been applied to aid interpretation of ice-rich or ice-remnant landforms on Mars. We focus on how glaciers and glacial landforms act to erode their surrounding landscape when they are active, and how they are preserved on the landscape when climate changes and ice retreats. This includes specific study of glaciers, debris-covered glaciers, rock glaciers, and cirques because glaciers act to erode landscapes, and landscapes contribute debris that can preserve glacier ice. We contextualize lobate debris aprons and glacier-like forms on Mars with debris-covered glaciers on Earth in order to put the latest research on both planets in a perspective aimed at maximizing process-based understanding of glacier evolution and ice preservation. While we primarily focus on processes controlling active debris-covered glaciers, a key to understanding glacier change through time is to consider individual landforms in context with the full-system environment in which they are found. We discuss process-based progressions and relationships between glacial landforms as understood on Earth; for example, the development of clean-ice glaciers, debris-covered glaciers, rock glaciers, moraines, and talus may be determined as a function of ice movement and debris input.

Building from our current knowledge of Mars, we show results from preliminary investigations of previously unmapped ice-remnant forms in Eastern Hellas and the Deuteronilis/Protonilus/Nilosyrtis Mensae regions that we have found using the recently available Context Camera (CTX) image mosaic (http://murray-lab.caltech.edu/CTX/). These landforms are newly identified small components of the martian glacial system, that are different from, but likely related to, glacier-like forms and recessional glacier-like forms. We also search for the cirque signature of ice erosion on Mars, and discuss how the timing of glacial, deglacial, and paraglacial activity may be further constrained by evaluating the existence and distribution of all possible components of a glacial landsystem. Interpretations of Mars from remote sensing alone can be evaluated against targeted interpretations on Earth using both remote sensing and field studies. In particular we will share on recent work studying debris sources and glacier evolution at Mt. Rainier, Washington state. By applying terrestrial understanding to Mars we aim to evaluate how present-day martian landforms are informative of past activity and conditions during times when orbital parameters, climate, and water-ice distribution were different.

How to cite: Koutnik, M., Pathare, A., Todd, C., and Johnson, E.: Ice preservation and landscape erosion during glacial retreat on Earth and Mars, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12630, https://doi.org/10.5194/egusphere-egu2020-12630, 2020.

High obliquity excursions on Mars are hypothesised to have redistributed water from the poles to nourish mid-latitude glaciers. Evidence of this process is provided by a variety of viscous flow features—ice-rich deposits buried beneath sediment mantle—located there today, including ‘lobate debris aprons’, or LDAs. During high obliquity extremes, ice may have persisted even nearer the equator, as indicated by numerous enigmatic moat-like depressions in the tropical Kasei Valles region. Numerous depressions surround isolated mesas and demarcate the past interaction between flowing lava and what were presumably ice-rich radial flows resembling today’s LDAs, but which have long since disappeared. Little is known about ‘ghost lobate debris aprons’ (ghost LDAs), besides their spatial extent as recorded by these depressions. This collection of ghost LDAs implies tropical ice loss over an area ~100,000 km². To constrain their history in Kasei Valles we derive model ages of different terrain types from crater counts. To constrain the volume of ice loss, we use a 2D perfect-plasticity model of ice flow to reconstruct the ghost LDA surfaces. Parametrised by the present surface topography and the range of yield stresses derived from radar interrogation of mid-latitude ice masses, the model reconstructs former ice surfaces along multiple flowlines orientated normal to ghost LDA boundaries. This reconstruction indicates between 1,300–3,300 km³ of ice—similar to that present in Iceland on Earth—was lost since lava emplacement ~1.4 Ga. Dating of these depressions shows that the ghost LDAs survived for ~800 million years following lava emplacement in the Kasei Valles region before their final demise.

How to cite: Hepburn, A., Ng, F., Holt, T., and Hubbard, B.: Ice-mass survival for approximately 800 Myr in the tropical Kasei Valles region, Mars, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-328, https://doi.org/10.5194/egusphere-egu2020-328, 2020.

The surfaces of Mercury and the Moon are covered with a layer of fragmental, highly heterogeneous material known as regolith. Regolith-related processes form short-scale textures seen in the high-resolution images. We carried out a survey of such textures on Mercury and compared them to better-known lunar analogs.

We surveyed the images obtained by MDIS NAC camera onboard the MESSENGER orbiter toward the end of the mission. We select images of the highest resolution and the finest sampling (less than 2.5 m/pix). We selected and screened ~3000 best images of that data set. To compare the typical surface morphology on Mercury to the Moon we used LROC NAC images. To facilitate the comparison we selected a representative set of LROC images that have the same sampling and sunlight incidence angles as the surveyed MDIS images, and degraded their quality.

Primarily, lunar and hermian surfaces as seen at high resolution are similar. The majority of decameter-scale topographic features are smooth and subdued due to the presence of regolith layer and its gardening. The majority of small impact craters are shallow and subdued. On the Moon, regolith-covered slopes, both steep and gentle, often have a specific subtle decameter-scale pattern referred as “elephant hide” or “leathery texture”. Its origin is unknown; however, it is almost certainly related to regolith transport. On Mercury, such a pattern is typically not observed: we identified it in a few occasions only.

Sharp slope breaks, “crisp” morphology and the absence of superposed degraded craters indicate geologically young “fresh” features that are characterized by thin or recently disturbed regolith. We observed fresh morphologies in one large young crater on Mercury; they were similar to their lunar counterparts. Hollows are unique “fresh” hermian features that have no close lunar analogs. They show exceptional sharpness at the highest resolution images, which indicates that their formation is ongoing or extremely recent. We found two more types of fresh morphologies that do not have close lunar analogs. (1) Finely-Textured Slope Patches (FTSP) are patches of finely (meter-scale) textured slopes with sharp outlines. This texture is characterized by a wavy chaotic pattern and occurs amid typical intercrater plains and old impact basins; there are no large young craters or hollows nearby, nor resolvable albedo or color peculiarities close to FTSP locations. They show semblance to some kinds of terrestrial landslides, which might suggest a variant of slide of thick regolith as their formation mechanism. (2) Chevron texture resembles scouring by wind or water in terrestrial environment; however, this cannot suggest a similar formation mechanism hermian conditions. Chevron texture found in one small part of the region with the super resolution images; it is oriented in the same direction. We initially a suggested that it could be related to a ray of a large young crater, but this was not perfectly consistent with observations.

In addition to the expected morphological similarity of regolith textures on the Moon and Mercury, the hermian surface displaces localized traces of geologically recent processes in the regolith having no lunar analogs.

How to cite: Zharkova, A., Kreslavsky, M., and Kolenkina, M.: Regolith textures on Mercury and the Moon, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-447, https://doi.org/10.5194/egusphere-egu2020-447, 2020.

Hillshade can greatly enhance the visualization of a surface for spatial analysis, graphical display or terrain extraction. However, its utilization is limited because the results depend on a particular sun azimuth and elevation. The image identification of geomorphologic units in shaded regions of the Moon, similarly, is affected by the azimuth and altitude of the sun. Therefore, utilize the advances while overcome the bias of hillshade, and then apply the modified hillshade to detect the geomorphologic units in shaded regions of the Moon will provide important methodological support for lunar topographic database construction. In this work, we optimize the traditional hillshade by enhancing the visibility of features in terms of scale, relief, orientation, and shape. The enhancement of the above topographic features is achieved by blending hillshaded terrain, curvature, slope, positive openness and sky-view factor into a remote sensing image. We select different study areas to test the modified hillshade, and find that the method proposed in this work can extract the basic geomorphologic units of the Moon in diverse terrain environments. Comparing to using the classic hillshaded digital elevation models, the boundary of various geomorphologic units is augmented and the extraction accuracy is improved using the modified hillshade.

How to cite: Wang, J., Liu, J., and Zhang, X.: Modified hillshade assists in the identification of geomorphologic units of the Moon, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7648, https://doi.org/10.5194/egusphere-egu2020-7648, 2020.

Under certain conditions, meter to house-sized boulders fall, jump, and roll from topographic highs to topographic lows, a landslide type termed rockfall. On the Moon, these features have first been observed in Lunar Orbiter photographs taken during the pre-Apollo era. Understanding the drivers of lunar rockfall can provide unique information about the seismicity and erosional state of the lunar surface, however this requires high resolution mapping of the spatial distribution and size of these features. Currently, it is believed that lunar rockfalls are driven by moonquakes, impact-induced shaking, and thermal fatigue. Since the Lunar Orbiter and Apollo programs, NASA’s Lunar Reconnaissance Orbiter Narrow Angle Camera (NAC) returned more than 2 million high-resolution (NAC) images from the lunar surface. As the manual extraction of rockfall size and location from image data is time intensive, the vast majority of NAC images have not yet been analyzed, and the distribution and number of rockfalls on the Moon remains unknown. Demonstrating the potential of AI for planetary science applications, we deployed a Convolutional Neural Network in combination with Google Cloud’s advanced computing capabilities to scan through the entire NAC image archive. We identified 136,610 rockfalls between 85°N and 85°S and created the first global, consistent rockfall map of the Moon. This map enabled us to analyze the spatial distribution and density of rockfalls across lunar terranes and geomorphic regions, as well as across the near- and farside, and the northern and southern hemisphere. The derived global rockfall map might also allow for the identification and localization of recent seismic activity on or underneath the surface of the Moon and could inform landing site selection for future geophysical surface payloads of Artemis, CLPS, or other missions. The used CNN will soon be available as a tool on NASA JPL’s Moon Trek platform that is part of NASA’s Solar System Treks (trek.nasa.gov/moon/).

How to cite: Bickel, V., Aaron, J., Manconi, A., Loew, S., and Mall, U.: A global rockfall map of the Moon powered by AI and Big Data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10003, https://doi.org/10.5194/egusphere-egu2020-10003, 2020.

Sediment transport in saltation is an important driver of the morphodynamics of planetary sedimentary surfaces and particularly responsible for the formation and evolution of aeolian ripples and dunes. When estimating the incidence and persistence of saltation on extraterrestrial planetary bodies, geomorphologists usually ask by how much the atmospheric winds on such bodies exceed the threshold value required to initiate saltation, a question that is inherently linked to the cohesiveness of a body's surface sediments. For example, there is currently an ongoing controversy about the saltation initiation threshold on Saturn's moon Titan because of strongly varying estimations of the cohesiveness of Titan's soils. If the value of this threshold is outside a certain relatively small range, the currently leading explanation for an observed mismatch between Titan's dune orientation and the predominant atmospheric wind direction is thought to break down. Here we put up for discussion an alternative viewpoint on the importance of cohesion and saltation initiation. First, we briefly review experimental and theoretical evidence from the literature suggesting that, in the field (in contrast to wind tunnel experiments), saltation is almost always easily initiated, which means that one mainly needs to understands whether saltation can be sustained once initiated. Second, we present results from DEM-based numerical simulations suggesting that saturated saltation, in particular the smallest wind speed at which it can be sustained (i.e., the cessation threshold), is almost unaffected by cohesion. Third, we show a simple theoretical conceptualization that explains these numerical results and, when implemented in an analytical model, captures existing cessation threshold and saltation transport rate measurements. Finally, we show that the predictions of this model are consistent with several direct and indirect observations associated with extraterrestrial saltation, including the orientation of Titan's dunes.

How to cite: Comola, F., Pähtz, T., and Duran, O.: Planetary saltation: Should we care about cohesion?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2188, https://doi.org/10.5194/egusphere-egu2020-2188, 2020.

The Colour and Stereo Surface Imaging System (CaSSIS) onboard the ExoMars Trace Gas Orbiter has been taking images of the surface of Mars at 4.5 metres/pixel in four colours since April 2018 and provides a new tool to study the geormophology of Mars. CaSSIS observations add to the existing data sets by increasing surface coverage, providing single stereo observations, and producing high signal to noise colour products. The data are being used to study seasonal dynamic phenomena up to a latitude of 74 degrees in both hemispheres. The colour products are being used to study the 2020 landing sites (Oxia Planum and Jezero crater) as well as studying the detailed topographic-compositional relationships in many regions of Mars. The presentation will provide a brief overview of the current data set and instrument capabilites, focussing on observations of polar processes and sedimentary deposits at all accessible latitudes.   

How to cite: Thomas, N. and Cremonese, G. and the The CaSSIS Team: Observations of polar and sedimentary processes on Mars with the CaSSIS imaging system , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22333, https://doi.org/10.5194/egusphere-egu2020-22333, 2020.

Catalogs of impact craters – not only a layers of objects in GIS but complete databases containing the morphometric and geomorphological characteristics – can help to solve such fundamental problems as the estimation of parameters of populations of impactors that collided with the surface of the planet throughout its history, as well as to clarify the processes of crater formation in the Solar System.

Currently, there are few global catalogues of Mercury that includes big craters only. For example: 1) global digital GIS-catalogue of Mercury’s craters created by the Braun University, USA. It is based on modern data gathered by MESSENGER and, along with approximately 9000 objects; it includes coordinates and diameters of large craters (> 20 km), exclusively. At the same time, it doesn’t contain any geomorphological information; 2) the other source is a geomorphological catalogue that was composed by Sternberg Astronomical Institute (SAI), which, while containing geomorphological information, was created in accordance to data of Mariner 10 and was presented as a text in a table. The SAI’s catalogue includes craters with a size of 10 km and larger. 

Creation of a new global catalog of Mercury’s craters based on the latest MESSENGER data is a comprehensive work. The catalog will consist of two subdirectories: 1) the geomorphological catalog of craters with a size of 10 km and larger; 2) the morphometric catalog of craters with a size less than 10 km. We use MESSENGER MDIS global mosaic of Mercury with resolution ~166 m/pixel and several MESSENGER DEMs – the first global Mercury DEM with resolution 665 m/pixel and four DEMs on Mercury quadrants with resolution ~222 m/pixel (which will be used for formation of a database of craters with diameters less than 10 km).

In addition to the required elements of any catalog (coordinates of craters and their diameters), we will be able to add full geomorphological description of craters, reduced to code designations (to simplify the implementation of the catalog in the GIS) and morphometric characteristics. For instance: 1) the diameter of the interior feature (flat floor, central peak, or inner ring); 2) depth and relative depth of each crater; 3) max and min slopes; 4) the average level of inclination of the external; 5) internal slopes of crater; 6) the ratio of volume of the crater rim to the volume of the bowl. The most of listed parameters can be calculated both for craters and for the surrounding surface.

By using this catalog, we will be able to quickly get statistics and create thematic maps, for example, maps of crater density on regions of interest.

This research was supported by Russian Foundation for Basic Research (RFBR), project No 20-35-70019.

How to cite: Kolenkina, M., Zharkova, A., Feoktistova, E., Rodionova, Z., and Kokhanov, A.: Creation of a new global geomorphological catalog of Mercury’s craters based on the latest MESSENGER data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8443, https://doi.org/10.5194/egusphere-egu2020-8443, 2020.

Geological mapping of Mercury is crucial to build an understanding of the history of the planet and to set the context for observations made by the recently launched BepiColombo mission when it begins science operations in orbit around Mercury in 2026. I am mapping the geology of the Debussy quadrangle (approximately 1/15th of the planet) as part of a pan-Europe program to map the entire planet at a scale of 1:3M using data from NASA’s MESSENGER mission. This will be the first high-resolution map of this part of Mercury. The mapped area includes the Rembrandt impact basin, the second largest on the planet, Enterprise Rupees, the longest tectonic fault as well as several explosive volcanic vents and terrains of different ages. Mapping began in October 2017 using ArcGIS software. The mapping follows the EU Plan map standards and USGS guidelines with linework drawn at 1:300k. Craters larger than 5 km have been outlined. Ejecta, where observed, is being traced for craters larger than 20 km and classified. Craters are classified based on crater degradation using both 3 class and 5 class schemes to enable comparison between historical and current maps of the rest of the planet and to enable placing features and units into context. A separate mapping layer for superficial shows the most recent modifications to Mercury’s surface, including volcanic deposits and impact craters. I present the map and with working geological interpretation.

How to cite: Pegg, D. L., Rothery, D. A., Balme, M. R., and Conway, S. J.: Geological Map Of The Debussy Quadrangle of The Planet Mercury , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22095, https://doi.org/10.5194/egusphere-egu2020-22095, 2020.

The Neruda Quadrangle (H-13), Mercury, is one of the final uncharted regions on the planet. With ESA-JAXA’s BepiColombo mission underway, it is imperative that a full set of comprehensive geological maps is produced prior to the spacecraft’s arrival, to provide context for BepiColombo’s studies. Geological mapping of H-13 has commenced as part of the PLANMAP project to map the entire planet at a scale of 1:3M [1–7].

Data and Methods: 

The primary base map to be used is the 166m/pixel high-resolution monochrome global mosaic. Additionally, the 665m/pixel enhanced colour global mosaic as well as narrow-angle camera (NAC) images are used for interpretation and quality control. All data were obtained by MESSENGER’s Mercury Dual Imaging System (MDIS). ArcGIS software is used for mapping following both USGS and PLANMAP practices. The map is projected as a Lambert Conformable Conic. To enable accurate correlation with neighbouring quadrangles, a 5° overlap is being mapped.

Mapping Units and Features: 

Mercury’s geological terrains are divided into four overarching units: Crater Materials, Smooth Plains, Intermediate Plains and Intercrater Plains [8]. Crater Materials are further subdivided based on the degree of crater degradation with both three class [2] and five class classifications being mapped [8].

Structural features such as lobate scarps, wrinkle ridges and high-relief ridges are distinguished using linework.

Acknowledgements:

Gratitude is given to STFC and the Open University Space Strategic Research Area that make this research possible (ST/T506321/1). PLANMAP is European Commission H2020 grant 776276.

References:

[1] Galluzzi et al (2017) EGU G. Assembly. [2] Galluzzi et al (2016) JoM, 12, 227–238. [3] Mancinelli et al (2016) JoM, 12, 190–202. [4] Guzzetta et al (2017) JoM, 3, 227–238. [5] Wright et al (2019) JoM, 15, 509–520. [6] Pegg et al (2019) LPSC Abstracts. [7] Malliband et al (2019) LPSC Abstracts. [8] Spudis & Guest (1988) Mercury.

How to cite: Man, B., Rothery, D. A., Balme, M. R., Conway, S. J., and Wright, J.: Geological Mapping of the Neruda Quadrangle (H13), Mercury, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22131, https://doi.org/10.5194/egusphere-egu2020-22131, 2020.

Introduction:  Eskers are sinuous sedimentary ridges that are widespread across formerly glaciated landscapes on Earth. They form when sediment in subglacial tunnels is deposited by meltwater. Some sinuous ridges on Mars have been identified as eskers; whilst some are thought to have formed early in Mars’ history beneath extensive ice sheets, smaller, younger systems associated with extant glaciers in Mars’ mid latitudes have also been identified. Elevated geothermal heating and formation during periods with more extensive glaciation have been suggested as possible prerequisites for recent Martian esker deposition.

Here, we adapt a model of esker formation with g and other constants altered to Martian values, using it initially to investigate the impact of Martian conditions on subglacial tunnel systems, before investigating the effect of varying water discharge on esker deposition.

Methods: To investigate the effect of these values on the operation of subglacial tunnel systems we first conduct a series of model experiments with steady water discharge, varying the assumed liquid density (r_w) from 1000 kgm^-3 to 1980 kgm^-3 (the density of saturated perchlorate brine) and ice hardness (A) from 2.4x10^-24 Pa^-3s^-1 to 5x10^-27 Pa^-3s^-1 (a temperature range of 0°C to -50°C). We then investigate the impact of variable water discharge on esker formation to simulate very simply a possible release of meltwater from an assumed geothermal event beneath a Martian glacier or ice cap.

Results and Discussion:  A key aspect of model behaviour is the decrease in sediment carrying capacity towards the ice margin due to increased tunnel size as ice thins. Our results suggest that Martian parameters emphasise this effect, making deposition more likely over a greater length of the conduit. Lower gravity has the largest impact; it reduces the modeled closure rate of subglacial tunnels markedly as this varies with overburden stress (and hence g) cubed. Frictional heating from flowing water also drops, but much less sensitively. Thus, for a given discharge, the tunnels tend to be larger, leading to lower water pressure and a reduction in flow power. This effect is amplified for harder ice. Higher inferred fluid density raises the flow power, but by a smaller amount.

These effects are clearly seen in the variable discharge experiments. Sediment is deposited on the falling limb of the hydrograph, when the tunnels are larger than the equivalent steady-state water discharge would produce. Sediment deposition occurs much further upglacier from the glacier snout, and occurs earlier on the falling limb leading to longer periods in which deposition occurs.

Conclusions: Our results suggest that esker formation within a subglacial meltwater tunnel would be more likely on Mars than Earth, primarily because subglacial tunnels tend to be larger for equivalent water discharges, with consequent lower water flow velocities. This allows sediment deposition over longer lengths of tunnel, and to greater depths, than for terrestrial systems. Future work will use measured bed topography of a mid-latitude esker to assess the impact of topography on deposition patterns and esker morphology, and we will expand the range of discharges and sediment supply regimes investigated.

How to cite: Arnold, N., Butcher, F., Gallagher, C., Balme, M., and Conway, S.: Modelling Esker Formation on Mars , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3463, https://doi.org/10.5194/egusphere-egu2020-3463, 2020.

Introduction: We observe internal flow structures within a viscous flow feature (VFF; 51.24°W, 42.53°S) interpreted as a debris-covered glacier in Nereidum Montes, Mars. The structures are exposed in the wall of a gully that is incised through the VFF, parallel to its flow-direction. They are near to the glacier terminus and appear to connect its deep interior (and possibly its bed) to arcuate flow-transverse foliations on its surface. Such foliations are common on VFF surfaces, but their relation to VFF-internal structures and ice flow is poorly understood. The VFF-internal structures we observe are reminiscent of up-glacier dipping shear structures that transport basal debris to glacier surfaces on Earth.

Subglacial environments on Mars are of astrobiological interest due to the availability of water ice and shelter from Mars’ surface radiation environment. However, current limitations in drilling technology prevent their direct exploration. If debris on VFF surfaces contains a component of englacial and/or subglacial debris, those materials could be sampled without access to the subsurface. This could reduce the potential cost and complexity of future missions that aim to explore englacial and subglacial environments on Mars.

Methods: We use a 1 m/pixel digital elevation model (DEM) derived from 25 cm/pixel High Resolution Imaging Science Experiment (HiRISE) stereo-pair images, and a false-colour (merged IRB) HiRISE image. We measured the dip and strike of the VFF-internal structures using ArcGIS 10.7 and QGIS software. We also input the DEM (and an inferred glacier bed topography derived from it) into ice flow simulations using the Ice Sheet System Model, assuming no basal sliding and present-day mean annual surface temperature (210K).

Results and Discussion: The VFF-internal structures dip up-glacier at ~20° from the bed. This is inconsistent with their formation by bed-parallel ice-accumulation layering without modification by ice flow. The VFF-internal structures and surface foliations are spectrally ‘redder’ than adjacent VFF portions, which appear ‘bluer’. This could result from differences in debris concentration and/or surficial dust trapping between the internal structures and the bulk VFF. Modelling experiments suggest that the up-glacier-dipping structures occur at the onset of a compressional regime as ice flow slowed towards the VFF terminus.

In cold-based glaciers on Earth, up-glacier-dipping folds are common approaching zones of enhanced ice rigidity near the glacier margin. Where multiple folds co-exist, the outermost typically comprises basal ice with a component of subglacial debris entrained in the presence of interfacial films of liquid water at sub-freezing temperatures. In polythermal glaciers, debris-rich up-glacier-dipping thrust faults form where sliding wet-based ice converges with cold-based ice.

Conclusions: We propose that the observed up-glacier-dipping VFF-internal structures are englacial shear zones formed by compressional ice flow. They could represent transport pathways for englacial and subglacial material to the VFF surface. The majority of extant mid-latitude VFF on Mars are thought to have been perennially cold-based; thus we favour the hypothesis that the VFF-internal structures are folds formed under a cold-based thermal regime. Under this mechanism, the outermost surface foliation, and its corresponding VFF-internal structure, is the most likely to contain subglacial debris.

How to cite: Butcher, F. E. G., Arnold, N. S., Berman, D. C., Conway, S. J., Davis, J. M., and Balme, M. R.: Possible Transport of Basal Debris to the Surface of a Mid-Latitude Glacier on Mars., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11628, https://doi.org/10.5194/egusphere-egu2020-11628, 2020.

Young gullies on Mars were first reported by Malin and Edgett in 2000 and were hailed as evidence of recent liquid water flows on Mars. Since that time, monitoring of gullies has revealed they are active today at times of year when the martian surface is at its coldest and when carbon dioxide ice is condensed on to the surface. In order to further explore the relationship between surface frosts and gully-activity we focus on Sisyphi Cavi near the south pole of Mars, where gully-activity has already been studied and CaSSIS obtained a dense temporal coverage in 2018. We identified the following sequence of events:

1) In winter frost covers all surfaces and dark spots and flows can be seen across the slopes with gullies and preferentially around the gully channels. This is consistent with previous observations and has been interpreted to be the surface expression of gas-jets generated by the sublimation of CO₂ underneath a continuous slab of CO₂ ice on the surface. The jets occur when the pressure fractures the slab ice and the pressurized gas can escape with entrained particles.

2) As the surface temperature increases towards 200 K, the top of the slopes are the first to defrost followed by sun facing parts of the alcoves and channels.

3) As the surface temperature approaches and exceeds 250 K and the surrounding terrain is completely defrosted, the last parts of the gully to remain frost covered are the fans. We interpret this to be a result of the fans having slightly lower thermal inertia than the surrounding materials. This lower thermal inertia could be because the fans have a lower content of water ice (i.e. a thicker lag on top of the ice-table), because of recent depositional events. It is at this time of year when gullies are most active. Hence, we infer that gully activity increases when there is both frosted and defrosted surfaces available to drive vigorous sublimation of the CO₂ ice.

4) Finally, once defrosting has almost fully completed and surface temperatures have reached their seasonal maximum of ~270 K the only remaining surface frosts are in pole-facing niches at the base of gully-alcoves.

Our study has underlined that the colour capability of the CaSSIS instrument is particularly suited to studying and monitoring changes in surface ices. Our observations reveal that gully-alcoves defrost before the fans and gullies defrost later than surrounding terrain – suggesting activity is driven by the availability of “hot” sediment to trigger more efficient sublimation. Further work will examine whether surface frost patterns differ between gullies that have been shown to be active and inactive since spacecraft observations began.

How to cite: Conway, S., Pommerol, A., Raack, J., Philippe, M., Mcewen, A., Thomas, N., and Cremonese, G.: Gullies on Mars and seasonal ices visualised using the Colour and Stereo Surface Imaging System (CaSSIS), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21643, https://doi.org/10.5194/egusphere-egu2020-21643, 2020.

In 2008, the High Resolution Imaging Science Experiment (HiRISE) on board NASA’s MRO fortuitously captured several discrete clouds of material in the process of cascading down a steep scarp of the water-ice-rich north polar layered deposits (NPLD). The events were only seen during a period of ~4 weeks, near the onset of martian northern spring in 2008, when the seasonal cover of CO2 is beginning to sublimate from the north polar regions. Russell et al. [1] analyzed the morphology of the clouds, inferring that the particles involved were mechanically analogous to terrestrial “dry, loose snow or dust”, so that the events were similar to terrestrial “powder avalanches” [2]. HiRISE confirmed the seasonality of avalanche occurrence the following spring, and continued to capture between 30 and 50 avalanches per season (fig. 1b,c) between 2008 and 2019, for a total of 7 Mars Years (MY29–MY35) of continuous scarp monitoring.

In this work we will present statistics on these events, in an attempt to quantify their effect on the mass balance of the NPLD, and with respect to competing processes such as viscous deformation and stress-induced block falls that do not trigger avalanches [3,4]. We also use a 1D thermal model [5] to investigate the sources and trigger mechanisms of these events. The model tracks the accumulation and ablation of seasonal CO2 frost on a martian surface. Russell et al. [1] support an initiation through gas-expansion related to the presence of CO2 frost on the scarp. Therefore the amount of frost that lingers on different sections of the model scarp at the observed time of the avalanches will provide evidence either for or against this particular mechanism. We will present preliminary results and discuss their implications.

References: [1] P. Russell et al. (2008) Geophys. Res. Lett. 35, L23204. [2] D. McClung, P.A. Schaerer (2006), Mountaineers, Seattle Wash. [3] Sori, M. M., et al., Geophys. Res. Lett., 43. [4] Byrne et al. (2016), 6th Int. Conf. Mars Polar Sci. Exploration [4] C. M. Dundas and S. Byrne (2010) Icarus 206, 716.

How to cite: Becerra, P., Conway, S., and Thomas, N. and the The HiRISE team: Avalanches of the martian north polar cap, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22331, https://doi.org/10.5194/egusphere-egu2020-22331, 2020.

Gravity affects sedimentation of particles suspended in water and gases in two ways: directly by the gravitational force that pulls a particle towards the surface and indirectly by the flow conditions of water or gas around the particles. The latter create a drag which is affected by the settling velocity. Consequently, drag coefficients observed on Earth sand-sized particles cannot be used on Mars because they are likely to overestimate the drag generated by the turbulent flow around the particle on Earth may shift into a more laminar state that generates lower drag. The effect of gravity on settling velocity is not linearly related to particle size, which may affect the sorting of the sand grains deposited from running water.  Experiments carried out during parabolic flights at reduced gravity indicate that the potential error in particle settling and sorting is significant, i.e. leading to wrong interpretations of the flow velocities at the time of deposition. This in turn has implications for reconstruction of Martian environmental conditions from rock textures determined from close-up imagery. This study uses computational fluid dynamics (CFD) modelling to independently assess the effect of gravity on sediment settling velocities and sediment sorting. The CFD modelling also offers a wide capability for reconstruction sedimentation on Mars and thus supports the reconstruction of it’s environmental past, as well as the search for traces of life. 

How to cite: Kuhn, N. J. and Trudu, F.: Computational Fluid Dynamics modelling of sedimentation on Mars, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3342, https://doi.org/10.5194/egusphere-egu2020-3342, 2020.

Surface erosion happened intensively of Mars in the Noachian, partly from precipitation and/or ice melting. However the exact method of erosion is poorly understood, despite various models are used for the Earth successfully. In this work we present the first test results of an erosion simulation GIS based system for Mars. The testing area is (2°55’ S, 111°53’ E) next to the Tinto Vallis,  was named after that Tinto-B. The main valley is ~ 81 km long, the average width is ~1.85 km, the average depth is ~ 250 m. From West there are several other but heavily eroded valleys, what join to the main valley. The used erosion-deposition model is SIMWE (SIMulated Water Erosion) (Mitasova et al, 2004) was applied to simulate the time limited erosion and deposition rate.

With the erosion-deposition simulation can also be used for targeting surface sampling missions beside reconstructing the ancient transport processes These ideal sampling locations might be barely visible on the DTMs or on the CTX, or HiRISE images - thus the modelling approach might help here also..

GRASS GIS 7.6 was used during the modeling starting from an elevation model and the x/y derivatives of the slope map. The script r.sim.water estimates the water depth and discharge from a simple rain event (mm/hr in min). For the erosion modelling r.sim.sediment script was used, what is the second part of the SIMWE model, what requires to calculate the detachment and transport coefficient and the shear stress of the analysed area.

The shear stress was determined az 1.0 as a default value, like the transport coefficient (value=0.01). The detachment  coefficient was calculated from the estimated K-factor of the analysed area and the calculated specific weight of water. The model use a 15mm/hr rain in 5 minutes long.

The results from the test area clearly show the main falls and debris skirts and also show the smaller erosion areas, what are not abundant on CTX and can’t be determined on the HRSC DTM. Using Earth based values as a first and rough approach, the transport limited erosion-deposition ranges from 0.0180 kg/ms² to -0.0166 kg/ms² where the positive values show the erosion and the negative values the deposition. Based on the experiences, we aim to develop further the model and adjust the physical parameters for more Mars relevant conditions. In the future we plan to running simulation, what show the possible landscape evolution in the past and in the future

Reference: Mitasova, H., Thaxton, C., Hofierka, J., Mclaughlin, R., Moore, A., & Mitas, L. (2004). Path sampling method for modeling overland water flow, sediment transport, and short term terrain evolution in Open Source GIS. Computational Methods in Water Resources: Volume 2, Proceedings of the XVth International Conference on Computational Methods in Water Resources Developments in Water Science, 1479-1490.

How to cite: Steinmann, V., Mari, L., and Kereszturi, Á.: Testing the SIMWE (SIMulate Water Erosion) model on a Martian valley system, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-204, https://doi.org/10.5194/egusphere-egu2020-204, 2020.

Wind flows on Mars are the dominant contemporary force driving sediment transport and associated morphological change on the planet’s dune fields. To fully understand the atmospheric – surface interactions occurring on the dunes, investigations need to be conducted at appropriate length scales (at or below that of any landform features being examined).

The spatial resolution of Martian Global Circulation Models (GCMs) is too low to adequately understand atmospheric-surface processes. Nevertheless, they can be utilised to establish initial state and boundary conditions for finer-scale simulations. Mesoscale atmospheric models have been used before to understand forcing and modification of entire dune fields. However, their resolution is still too coarse to fully understand interactions between the boundary layer and the surface. This study aims to examine and improve our understanding of local-scale processes using microscale (e.g., 1.5m cell spacing) airflow modelling to better investigate localised topographic effects on wind velocity and associated aeolian geomorphology.

Toward these aims, this study will simulate microscale wind flow using computational fluid dynamics software (OpenFOAM) at a series of sites containing a variety of topographies and wind regimes. A Mars GCM will provide input for baseline mesoscale modelling runs, the output of which will then be used as input for microscale airflow modelling. The sites used for the study will have excellent orbital, or preferentially, in situ data coverage. Detailed HiRISE imagery will provide high-resolution Digital Terrain Models (DTMs) which will be used by the OpenFOAM simulations. Results from model simulations will be evaluated/validated using both in situ data and geomorphic analysis of imagery.

How to cite: Love, R., Jackson, D. W. T., Cooper, J. A. G., Avouac, J.-P., Smyth, T. A. G., and Michaels, T. I.: Surface wind flow modelling on Mars using Computational Fluid Dynamics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-335, https://doi.org/10.5194/egusphere-egu2020-335, 2020.

The duration and timing of a northern ocean is a key issue in understanding the past geological and climatic evolution of Mars. Mars experienced its greatest loss of H₂O between the Noachian and Late Hesperian (~10 m Global Equivalent Layer, Jakosky et al., 2017) roughly the same amount that is thought to have been added to the global inventory by extrusive volcanism over the same time period (Carr and Head, 2015). Thus, the total inventory of water was probably similar during these two epochs. But, the ocean during the Late Hesperian was smaller in extension than the ocean during the Noachian– with significant implications for the potential origin and survival of life. Here we examine the implications of the existence of a Late Hesperian/ Early Amazonian ocean on the planet’s inventory of water (and especially liquid water) and its variation with time. Our previous work (Rodriguez et al., 2016; Costard et al., 2017) concluded that the most plausible explanation for the origin of the Thumbprint Terrain (TT) lobate deposits, with run-ups, found along the dichotomy boundary, especially in Arabia Terra, was tsunami deposits. This supports the hypothesis that an ocean occupied the northern plains of Mars as recently as ~3 billion years ago. Furthermore, Costard et al (2017) produced a tsunami numerical model showing that the TT deposits exhibit fine-scale textural patterns due to the wave’s interference patterns resulting from interactions with the coastal topography. More recently, we suggested that the unusual characteristics of Lomonosov crater (50.52°N/16.39°E ) in the northern plains are best explained by the presence of a shallow ocean at the time of the impact (Costard et al., 2019). Interestingly, the apparent agreement between the age of the Lomonosov impact and that of the TT unit (~3 Ga), strongly suggests that it was the source of the tsunami (Costard et al., 2019). Our preliminary assessment indicates that this impact-generated tsunami required a mostly liquid ocean and because of the high latitude location of the Lomonosov crater site, our results strongly imply relatively warm paleoclimatic conditions. Our conclusions highlight the need for more sophisticated climate models.

How to cite: Costard, F., Rodriguez, J. A. P., Séjourné, A., Lagain, A., Clifford, S., Ormö, J., Bouley, S., Kelfoun, K., and Lavigne, F.: Tsunami on Mars: Implications for the duration and timing of a northern ocean, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5824, https://doi.org/10.5194/egusphere-egu2020-5824, 2020.

   Channel systems on both Earth and Mars present several morphological similarities suggesting that they are the results of relatively similar mechanisms in the spatial and temporal contexts. Our research focuses on investigating discontinuous channels, morphologically defined as channel segments interrupted by unchanneled reaches or as a set of streams interrupted over space. These systems are unfrequently found on Mars or Earth [1], therefore signify an indication of special topographic, hydrologic or lithologic conditions.

   A draft classification takes into account that discontinuities can be classified into major groups according to their origin and geological setting: 1) Arid region discontinuities. 2) Sinking streams in lava and karsts terrains. 3) Fluvio-lacustrine, continental shelves, and deep-sea discontinuities. 4) Other types as post fluvial effects that obliterate channel sections by impact cratering, Sediment covers, mudflows intersecting and filling in the channel in addition to the selective channel material removal.

   We characterized such drainage systems on Mars, in the Navua Valles paleo drainage system [2], and near Saheki crater, both situated in the northern flank of Hellas Basin. While on Earth, we identified a number of similar settings as analogs to those identified on Mars, in arid regions such as in Mojave river (USA), and the Sahara Desert (Algeria).

   Furthermore, an unusual type of martian analog on Earth was identified in the subsea using bathymetric maps, as we located discontinuous segments in various continental shelf locations to the western coast of North America [3] and to the northwest African margin in Mauritania [4]. Our preliminary investigation suggests that discontinuous channel morphologies in terrestrial dryland may be similar to those in the seafloor on a larger scale.

   The West African continental shelf confines a discontinuity in the paleo drainage rivers system flowing from the Tamanrasset paleo drainage river to Cap Timiris submarine canyon system [4]. That unmapped channel segments are believed to occur due to the change of kinetic energy on the sea bottom at relatively less sloping, then the channels reappear at the edge of continental shelves as a result of slope change. The topographic profile of a selected site southeast to Saheki crater on Mars manifested a similar topography to a continental shelf- submarine canyon system. The martian site is suggested to be a paleolake.

   As a preliminary result of our study, we emphasize that the discontinuous behavior of submarine channels on terrestrial continental shelves might be a relevant analog for understanding similar martian drainage systems and further expand geomorphological studies for a new branch of martian-terrestrial analogs in the subsea.

References:

[1] Hargitai H. et al. 2017. Discontinuous Drainage Systems Formed by Precipitation and Ground-Water Outflow in the Navua Valles and Southwest Hadriacus Mons, Mars. [2] Ettahri M.A & Hargtiai H. 2019. Discontinuous valley networks on Mars: A comparative survey. EPSC-DPS2019-1565-2. [3] Maier K.L. et al. 2011. The elusive character of discontinuous deep-water channels: New insights from Lucia Chica channel system, offshore California. [4] Skonieczny C. et al. 2015. African humid periods triggered the reactivation of a large river system in Western Sahara.

How to cite: Ettahri, M. A.: Terrestrial Submarine Discontinuous Systems as Analogs for Similar Martian Channel Morphologies., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19893, https://doi.org/10.5194/egusphere-egu2020-19893, 2020.