Active gullies on Mars

Post by Dr. Colin Dundas, U.S. Geological Survey, Astrogeology Science Center

Martian “gullies” are a class of landforms on steep slopes, characterized by an upper alcove and a depositional apron, linked by a channel. On Earth, similar features would likely be termed ravines or alluvial fans. The Martian features usually appear geomorphically fresh, with sharply defined channels and no superposed impact craters. Changes were first detected in Martian gullies over a decade ago, and such observations have become more common as high-resolution repeat image coverage has expanded. This current activity correlates with seasonal frost (which is mostly CO2 on Mars) and has resulted in substantial modification of some gullies, leading to a debate over whether CO2 alone is sufficient to form them without liquid water.

PGIM_Jan2018_Fig1

Image 1: Subsection of HiRISE image ESP_023809_1415 (https://www.uahirise.org/ESP_023809_1415) at reduced resolution, providing context and an overview of the gully system. North is up and light is from the upper left.

The image in this post shows an example of a change in a gully near 38°S, 224°E. Image 1 shows the gully system, part of a cluster on a crater wall. The slope faces south (towards the pole), and preferentially develops seasonal frost in the winter since it is colder and more shadowed. Image 2 shows before-and-after images. The upper arrow indicates a location where material has been eroded within the channel; the middle arrow indicates a deposit filling the lower part of the channel, terminating at the bottom arrow. Planet-wide, dozens of events in gullies have now been observed (Dundas et al., in press), ranging from superficial changes in albedo to large-scale channel erosion and deposition of lobate, boulder-rich flows.

PGIM_Jan2018_Fig2

Image 2: Full-resolution subsections of ESP_023809_1415 (left panel, August 25, 2011) and ESP_047057_1415 (right panel, August 10, 2016; https://www.uahirise.org/ESP_047057_1415) showing changes in the gully, discussed in the text. North is up and light is from the upper left.

Further reading:

Conway, S. J., Balme, M. R., 2016. A novel topographic parameterization scheme indicates that Martian gullies display the signature of liquid water. Earth Planet. Sci. Lett., 454, 36-45, doi:10.1016/j.epsl.2016.08.031.

Diniega, S., Byrne, S., Bridges, N.T., Dundas, C.M., McEwen, A.S., 2010. Seasonality of present-day Martian dune-gully activity. Geology, 38, 1047-1050, doi:10.1130/G31287.1.

Dundas, C. M., McEwen, A. S., Diniega, S., Hansen, C. J., Byrne, S., McElwaine, J. N. The formation of gullies on Mars today. Geol. Soc. London Spec. Pub., 467, doi:10.1144/SP467.5.

Harrison, T. N., Osinski, G. R., Tornabene, L. L., Jones, E., 2015. Global documentation of gullies with the Mars Reconnaissance Orbiter Context Camera and implications for their formation. Icarus, 252, 236-254, doi:10.1016/j.icarus.2015.01.022.

Hoffman, N., 2002. Active polar gullies on Mars and the role of carbon dioxide. Astrobiology, 2, 313–323, doi:10.1089/153110702762027899.

Malin, M.C., Edgett, K.S., 2000. Evidence for recent groundwater seepage and surface runoff on Mars. Science, 288, 2330-2335, doi:10.1126/science.288.5475.2330.

Malin, M.C., Edgett, K.S., Posiolova, L.V., McColley, S.M., Dobrea, E.Z.N., 2006. Present-day impact cratering rate and contemporary gully activity on Mars. Science, 314, 1573–1577, doi:10.1126/science.1135156.

Pelletier, J.D., Kolb, K.J., Kirk, R.L., 2008. Recent bright gully deposits on Mars: Wet or dry flow? Geology, 36, 211–214, doi:10.1130/G24346A.1.

Pilorget, C., Forget, F., 2016. Formation of gullies on Mars by debris flows triggered by CO2 sublimation. Nature Geosci., 9, 65-69, doi:10.1038/ngeo2619.

Vincendon, M., 2015. Identification of Mars gully activity types associated with ice composition. J. Geophys. Res. Planets, 120, doi:10.1002/2015JE004909.

 

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1 Comment

  1. Ben Everitt

     /  January 3, 2018

    Interesting discussion. I was a pimply-faced graduate student in 1967 when the Lunar Orbiter images began arriving, and we were fascinated by close-ups of sinuous rilles and other channel-like features. In particular I remember the avalanche chutes on the steep slopes of fresh craters like Copernicus, very similar to the Martian examples pictured here. The water enthusiasts of course wanted the moon to have had a wet history. It would be interesting to review the short history of the “water on the moon hypothesis” in the context of Martian geology. In my mind, the primary question has yet to be satisfactorily answered: On earth it has been generally assumed that debris avalanching involves entrapped gas, yet we see dry debris avalanches on the moon in the absence of both water and atmosphere. More data on initiation slope, runout slope at toe, and other morphological characteristics under different gravity regimes will begin to provide answers, as our mapping of both the Moon and Mars improves.

    Reply

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