| Title: |
The Dynamics of CO2‐Driven Granular Flows in Gullies on Mars. |
| Authors: |
Roelofs, Lonneke1 (AUTHOR) l.roelofs@uu.nl; Conway, Susan J.2 (AUTHOR); van Dam, Bas1 (AUTHOR); van Eijk, Arjan1 (AUTHOR); Merrison, Jonathan P.3 (AUTHOR); Iversen, Jens Jacob3 (AUTHOR); Sylvest, Matthew4 (AUTHOR); Patel, Manish R.4 (AUTHOR); Markies, Henk1 (AUTHOR); van Maarseveen, Marcel1 (AUTHOR); McElwaine, Jim5 (AUTHOR); Kleinhans, Maarten G.1 (AUTHOR); de Haas, Tjalling1 (AUTHOR) |
| Source: |
Journal of Geophysical Research. Planets. Jun2024, Vol. 129 Issue 6, p1-22. 22p. |
| Subject Terms: |
*Volcanic ash, tuff, etc.; *Earthflows; *Debris avalanches; Granular flow; Mars (Planet); Solar cycle; Discrete element method |
| Abstract: |
Martian gullies are landforms consisting of an erosional alcove, a channel, and a depositional apron. A significant proportion of Martian gullies at the mid‐latitudes is active today. The seasonal sublimation of CO2 ice has been suggested as a driver behind present‐day gully activity. However, due to a lack of in situ observations, the actual processes causing the observed changes remain unresolved. Here, we present results from flume experiments in environmental chambers in which we created CO2‐driven granular flows under Martian atmospheric conditions. Our experiments show that under Martian atmospheric pressure, large amounts of granular material can be fluidized by the sublimation of small quantities of CO2 ice in the granular mixture (only 0.5% of the volume fraction of the flow) under slope angles as low as 10°. Dimensionless scaling of the CO2‐driven granular flows shows that they are dynamically similar to terrestrial two‐phase granular flows, that is, debris flows and pyroclastic flows. The similarity in flow dynamics explains the similarity in deposit morphology with levees and lobes, supporting the hypothesis that CO2‐driven granular flows on Mars are not merely modifying older landforms, but they are actively forming them. This has far‐reaching implications for the processes thought to have formed these gullies over time. For other planetary bodies in our solar system, our experimental results suggest that the existence of gully like landforms is not necessarily evidence for flowing liquids but that they could also be formed or modified by sublimation‐driven flow processes. Plain Language Summary: Gullies on Mars are features that look like landforms carved by debris flows on Earth. At the top, the gullies have an erosional alcove where material is eroded and at the bottom of the gully, a fan exists where this material is deposited. For a long time, it was believed that these gullies were formed by liquid water, just like on Earth. However, Martian gullies are active today, which cannot be reconciled with the lack of liquid water on the surface of Mars. Data from satellites has shown that the activity in Martian gullies is correlated to a seasonal cycle of CO2 ice deposition and sublimation. However, we still do not know whether and how CO2 sublimation produces the observed changes in gullies. Here we show the results of experiments in environmental chambers in which we created CO2‐driven flows under Martian conditions. The experiments show that granular material can be fluidized by sublimation of CO2 ice. Furthermore, the flow dynamics and morphology of the deposits are similar to debris flows and pyroclastic flows on Earth. This explains the similarity between the Martian gullies and the water‐shaped gullies on Earth without the presence of liquid water on the surface of Mars today. Key Points: The sublimation of small amounts of CO2 ice can fluidize granular material on low slopes under Martian atmospheric pressureThe flow dynamics of CO2‐driven flows are similar to that of terrestrial fluidized two‐phase flows, for example, debris flows and dense pyroclastic flowsExperimental CO2‐driven granular flows create deposit morphologies similar to those observed in Martian gullies [ABSTRACT FROM AUTHOR] |
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| Database: |
GreenFILE |