Evidence against vast glaciation in Mars’ grandest canyons

Post by Miss. L. Kissick, PhD candidate, Department of Earth Sciences, University of Oxford. Research conducted while at the Department of Geography, Durham University.

The Valles Marineris (Image 1) form the largest system of interconnected canyons on Mars, up to 2000 km long and in parts 10 km deep, and have long been a focal point of interest in planetary geomorphology. Recently, researchers including Mège and Bourgeois (2011), Cull et al. (2014), and Gourronc et al. (2014) outlined the case for a vast glaciation filling these canyons to several kilometres in depth. The implications of such a fill on the climate history and global water budget of Mars would be paradigm-shifting, but with high resolution imagery, features attributed as glacial may be better explained by more common geomorphological processes.

IM1

Image 1: Valles Marineris in Mars Orbital Laser Altimeter topography. This enormous canyon system is in parts 10 km deeper than the surrounding plateau, and was hypothesised to contain a glacier of a volume comparable to each Martian polar cap (Gourronc et al., 2014). Rough areas described in Image 2 are circled. Image adapted from Figure 1 of Kissick and Carbonneau (2019).

In Image 2, several features attributed to formation by glacial erosion are discredited when viewed in the 25 cm/pixel imagery of the High Resolution Imaging Science Experiment camera (HiRISE). These include a lateral moraine in Figure 2A as described by Gourronc et al. (2014), which on Earth are rubbly mounds of glacially-eroded sediment that accumulates at the edges of valley glacier margins. Up close, however, these bench-like platforms protruding from the walls of Coprates Chasma in eastern Marineris show regular, organised layering more like strata, disagreeing with moraines’ characteristic disorganised hummocks. In Figure 2B we see the ‘glacial trimline’ also described in the same paper; trimlines form by the erosive topmost layer of glaciers riving themselves against their containing valley’s walls. In HiRISE resolution, however, this boundary down the walls of Marineris is discontinuous and appears to be different levels of bedrock strata. In a final example, in Figure 2C apparent hollows interpreted by Gourronc et al. (2014) as kettle holes in Candor Chasma (pits formed by the melting of stranded glacial ice) are actually ridges comprised of individual mounds, as seen up close in Figure 2D. The origins of this unusual feature are as-yet unclear, as it has only been identified in this specific area, but they may be an advanced form of mesa degradation.

IM2

Image 2: Features previously attributed to glacial processes that may be more readily explained by widespread geomorphological alternatives. A) Layered strata in a feature attributed to lateral moraine in Coprates Chasma; B) Multiple layers across a glacial ‘trimline’ suggests this continuous boundary down the sides of Marineris is bedrock strata rather than an ice-carved erosional fill level; C) ‘Kettle holes’ are with high resolution actually comprised of ridges composed of individual mounds; D) A closer look at these mounds; note the shadows to the south-east. All images adapted from Figures 4, 10, and 12 of Kissick and Carbonneau (2019).

After extensive scrutiny across Marineris over multiple types of mapped glacial features, the research we published this month in the journal Icarus suggests the hypothesis of a widespread Marineris glaciation does not agree with observed geomorphology. This conclusion is also more in keeping with our understanding of Martian climate and does not require major re-estimations of the planet’s water budget. Please see Kissick and Carbonneau (2019) for more information.

Further Reading

Cull, S. et al. A new type of jarosite deposit on Mars: Evidence for past glaciation in Valles Marineris? Geology 42.11, 959-962.

Gourronc, M., et al. (2014), One million cubic kilometers of fossil ice in Valles Marineris: Relicts of a 3.5 Gy old glacial landsystem along the Martian equatorGeomorphology 204, 235-255.

Kissick, L. E. and Carbonneau, P. E. (2019), The case against vast glaciation in Valles Marineris, Mars, Icarus 321, 803-823.

Mège, D. and Bourgeois, O. (2011). Equatorial glaciations on Mars revealed by gravitational collapse of Valles Marineris wallslopesEarth and Planetary Science Letters 310, 182-191.

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1 Comment

  1. Haruki Chou

     /  April 15, 2019

    Why this page so narrow?
    Using less than 1/3 of my monitor’s width…
    Bad website design.

    Reply

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