Reconstructing glaciers on Mars

Post by Dr. Stephen Brough, School of Geography, Politics and Sociology, Newcastle University, UK.

There exist thousands of putative debris-covered glaciers in the mid-latitudes of Mars (e.g. Souness et al., 2012; Levy et al., 2014). Much like their terrestrial counterparts, many of these glaciers have undergone mass loss and recession since a former glacial maximum stand (e.g. Kargel et al., 1995; Dickson et al, 2008) (Image 1). However, there is a lack of knowledge regarding the volume of ice lost since that time and whether such recession has been spatially variable. Reconstructing glacial environments based on their landforms and structural assemblage is a powerful concept applied in terrestrial glaciology. Through utilising evidence left on the landscape with observations from modern glaciers, it is possible to reconstruct the extent and dynamics of both former (glaciated) and modern (glacierised) glacial environments (see Bennett and Glasser, 2009). This month’s planetary geomorphology post investigates how similar techniques have been utilised to reconstruct the former extent of glaciers on our planetary neighbour, Mars.

Image_1

Image 1: Glacier recession on Earth and Mars. (a – b) Location of martian glacier in the Phlegra Montes region of Mars’ northern hemisphere (~164.48 oE, ~34.13 oN). Background is MOLA elevation overlain on THEMIS-IR daytime image. (c) Near terminus Context Camera (CTX) image expansion of Phlegra Montes martian glacier. White arrows indicate arcuate ridges in glacier forefield that occupies the southern half of image. Subset of CTX image P16_007368_2152_XN_35N195W. (d) The forefield of terrestrial Midre Lovénbreen, Svalbard, is shown for comparison. White arrows indicate arcuate terminal moraine indicating the glacier’s former expanded extent. Modified from Hubbard et al., 2014.

Of particular geomorphological significance for reconstructing the former extent of an ice mass, are ice-marginal landforms such as moraines and trimlines (Image 1d). These landforms provide a means to reconstruct the changing position (both spatially and vertically) of a glacier through time. Image 2 shows one particular debris-covered glacier, located in Crater Greg on Mars’ southern hemisphere. An oblique 3D view of the same feature is visible in Image 3. Outside of the interpreted present day ice mass are a nested series of multiple ridges (10s of metres in height) aligned parallel to each other (Image 2a). Several authors have described and interpreted these ridges as being latero-terminal moraines, likely formed by sediment deposition or reworking by flowing ice masses (Arfstrom and Hartmann, 2005; Hubbard et al., 2011; Hartmann et al., 2014). The appearance of nested moraine ridges suggests that the glacier was subjected to apparently punctuated mass loss and recession since attaining its former maximum extent. Using this geomorphological evidence to determine the glacier’s maximum extent (Image 2b) revealed that the glacier had lost an area of 6.86 km2, or an approximate 70% reduction in area from its maximum recorded extent (Brough et al., 2016). Coupling this area loss with differences in elevation between the current surface and theoretically reconstructed palaeo-glacier surfaces (e.g. Image 2c) revealed that the glacier had lost a volume of between 0.18 and 0.52 km3 (Brough et al.; 2016a). The glacier in Crater Greg has therefore undergone substantial mass loss since formation, with these changes manifested in both surface lowering and terminus recession (Image 2 and 3).

Image_2

Image 2: Glacierised landscape in Crater Greg (∼113.16 oE, ~38.15 oS). (a) Schematic illustration of the inferred moraine sequence (black and white lines) recorded in the geomorphological record. (b) Interpreted current (blue line) and former maximum (green line) extent of the glacier as identified by Brough et al. (2016). (c) Example of reconstructed palaeo-glacier surface of Brough et al. (2016), with 50m contours overlain. HiRISE image PSP_002320_1415_RED.

Image_3

Image 3: A 3D oblique perspective of the scene shown in Image 2 made with a HiRISE stereo Digital Terrain Model (DTM). The glacier can be seen occupying an approximately 3 km wide upper basin. The sequence of at least three raised arcuate ridges can be seen in the lower half of the image. The GLF shows evidence, through deformed chevron-like surface ridges visible in the upper basin, of down-slope flow. HiRISE image PSP_002320_1415_RED draped over DTM made from stereo images PSP_002320_1415_RED and PSP_003243_1415_RED. Modified from Hubbard et al., 2011.

Through studies such as those introduced above we are improving our understanding of several important planetary issues such as (i) how Mars’ present-day landscape was formed and how it might evolve in the future, (ii) the presence and phase state of H2O on/close to Mars’ surface, and (iii) how Mars’ climate has changed in geologically recent history. However, our understanding of these issues is far from complete and there are many interesting and perplexing research questions outstanding (see Hubbard et al., 2014). For example, relatively little is known about the processes and former climates under which these glaciers formed, or how they have evolved over time. On Earth, numerical glacier flow modelling provides one such technique to link historical or geological observations of glacier fluctuations to the environmental and climatic conditions that were responsible for their formation and is an exciting area of ongoing research on Mars, so stay tuned for further updates!

Further Reading

Arfstrom, J. and Hartmann, W. K. (2005) Martian flow features, moraine-like ridges, and gullies: Terrestrial analogs and interrelationships. Icarus, 174, 321-335. http://doi.org/10.1016/j.icarus.2004.05.026.

Bennett, M. R. and Glasser, N. F. (2009) Glacial Geology: ice sheets and landforms. Wiley-Blackwell, Chichester.

Brough, S., Hubbard, B. and Hubbard, A. (2016) Former extent of glacier-like forms on Mars. Icarus, 274, 37-49. http://doi.org/10.1016/j,icarus.2016.03.006.

Dickson, J. L., Head, J. W. and Marchant, D. R. (2008) Late Amazonian glaciation at the dichotomy boundary on Mars: Evidence for glacial thickness maxima and multiple glacial phases. Geology, 36, 411-414. http://doi.org/10.1130/g24382a.1.

Hartmann, W. K., Ansan, V., Berman, D. C., Mangold, N. and Forget, F. (2014) Comprehensive analysis of glaciated martian crater Greg. Icarus, 228, 96-120. http://doi.org/10.1016/j.icarus.2013.09.016.

Hubbard, B., Milliken, R. E., Kargel, J. S., Limaye, A. and Souness, C. (2011) Geomorphological characterization and interpretation of a mid-latitude glacier-like form: Hellas Planitia, Mars. Icarus, 211, 330-346. http://doi.org/10.1016/j.icarus.2010.10.021.

Hubbard, B., Souness, C. and Brough, S. (2014) Glacier-like forms on Mars. Cryosphere, 8, 2047-2061. http://doi.org/10.5194/tc-8-2047-2014.

Kargel, J. S., Baker, V. R., Beget, J. E., Lockwood, J. F., Pewe, T. L., Shaw, J. S. and Strom, R. G. (1995) Evidence of Ancient Continental-Glaciation in the Martian Northern Plains. J. Geophys. Res. Planets, 100, 5351-5368. http://doi.org/10.1029/94je02447.

Levy, J. S., Fassett, C. I., Head, J. W., Schwartz, C. and Watters, J. L. (2014) Sequestered glacial ice contribution to the global Martian water budget: Geometric contstraints on the volume of remnant, midlatitude debris-covered glaciers. J. Geophys. Res. Planets, 119, 2014JE004685. http://doi.org/10.1002/2014je004685.

Parsons, R. and Holt, J. (2016) Constraints on the formation and properties of a Martian lobate debris apron: insights from high-resolution topography, SHARAD radar data, and a numerical ice flow model. J. Geophys. Res. Planets, 121, 432-453. http://doi.org/10.1002/2015je004927.

Souness, C., Hubbard, B., Milliken, R. E. and Quincey, D. (2012) An inventory and population-scale analysis of martian glacier-like forms. Icarus, 217, 243-255. http://doi.org/10.1016/j.icarus.2011.10.020.

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