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Article

Discrete Element Modelling of Pit Crater Formation on Mars

by 1,2
1
ICREA (Institució Catalana de Recerca i Estudis Avançats), Passeig Lluís Companys 23, 08010 Barcelona, Spain
2
Departament de Dinàmica de la Terra i de l’Oceà, Facultat de Ciències de la Terra, Universitat de Barcelona, C/Martí i Franqués s/n, 08028 Barcelona, Spain
Academic Editors: Jesus Martinez-Frias and Giovanni Barreca
Geosciences 2021, 11(7), 268; https://doi.org/10.3390/geosciences11070268
Received: 31 May 2021 / Revised: 11 June 2021 / Accepted: 20 June 2021 / Published: 24 June 2021
(This article belongs to the Section Structural Geology and Tectonics)
Pit craters are now recognised as being an important part of the surface morphology and structure of many planetary bodies, and are particularly remarkable on Mars. They are thought to arise from the drainage or collapse of a relatively weak surficial material into an open (or widening) void in a much stronger material below. These craters have a very distinctive expression, often presenting funnel-, cone-, or bowl-shaped geometries. Analogue models of pit crater formation produce pits that typically have steep, nearly conical cross sections, but only show the surface expression of their initiation and evolution. Numerical modelling studies of pit crater formation are limited and have produced some interesting, but nonetheless puzzling, results. Presented here is a high-resolution, 2D discrete element model of weak cover (regolith) collapse into either a static or a widening underlying void. Frictional and frictional-cohesive discrete elements are used to represent a range of probable cover rheologies. Under Martian gravitational conditions, frictional-cohesive and frictional materials both produce cone- and bowl-shaped pit craters. For a given cover thickness, the specific crater shape depends on the amount of underlying void space created for drainage. When the void space is small relative to the cover thickness, craters have bowl-shaped geometries. In contrast, when the void space is large relative to the cover thickness, craters have cone-shaped geometries with essentially planar (nearing the angle of repose) slope profiles. Frictional-cohesive materials exhibit more distinct rims than simple frictional materials and, thus, may reveal some stratigraphic layering on the pit crater walls. In an extreme case, when drainage from the overlying cover is insufficient to fill an underlying void, skylights into the deeper structure are created. This study demonstrated that pit crater walls can exhibit both angle of repose slopes and stable, gentler, collapse slopes. In addition, the simulations highlighted that pit crater depth only provides a very approximate estimate of regolith thickness. Cone-shaped pit craters gave a reasonable estimate (proxy) of regolith thickness, whereas bowl-shaped pit craters provided only a minimum estimate. Finally, it appears that fresh craters with distinct, sharp rims like those seen on Mars are only formed when the regolith had some cohesive strength. Such a weakly cohesive regolith also produced open fissures, cliffs, and faults, and exposed regolith “stratigraphy” in the uppermost part of the crater walls. View Full-Text
Keywords: Mars; tectonics; morphology Mars; tectonics; morphology
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MDPI and ACS Style

Hardy, S. Discrete Element Modelling of Pit Crater Formation on Mars. Geosciences 2021, 11, 268. https://doi.org/10.3390/geosciences11070268

AMA Style

Hardy S. Discrete Element Modelling of Pit Crater Formation on Mars. Geosciences. 2021; 11(7):268. https://doi.org/10.3390/geosciences11070268

Chicago/Turabian Style

Hardy, Stuart. 2021. "Discrete Element Modelling of Pit Crater Formation on Mars" Geosciences 11, no. 7: 268. https://doi.org/10.3390/geosciences11070268

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