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Olympus Mons, lopsided giant 11 February 2009

Posted by admin in current research, geoscience, Mars, solar system, volcanology.
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Mosaic of Olympus Mons (NASA/NSSDC).

Olympus Mons, the largest mountain and the largest volcano we know of in the Solar System, is a huge shield volcano on Mars. It rises 23km above the Martian plain, is approximately 600km in diameter, and is lopsided, like a vast unsuccessful cake. The gently-sloping north-west flank of the volcano extends much further from the central caldera complex than does the steeply-sloping south-eastern flank; these flanks are also upwardly concave, showing an overall increase in the steepness of slope towards the centre, and are divided from the surrounding terrain by steep scarps, features not found in other sectors. A new paper on Olympus Mons in the February 2009 issue of Geology looks at the possible reasons for what it calls these ‘substantial asymmetries in its structure’. From the abstract:

The NW-SE asymmetries are aligned with the regional slope from the Tharsis rise, but an understanding of the underlying causes has remained elusive. We use particle dynamics models of growing, spreading volcanoes to demonstrate that these flank structures could reflect the properties of the basement materials underlying Olympus Mons. We find that basal slopes alone are insufficient to produce the observed concave-upward slopes and asymmetries in flank extent and deformation style that are observed at Olympus Mons; instead, lateral variations in basal friction are required. These variations are most likely related to the presence of sediments, transported and preferentially accumulated downslope from the Tharsis rise. Such sediments likely correspond to ancient phyllosilicates (clays) recently discovered by the Mars Express mission.

Thus the north-west flank of the edifice spreads more easily across the thickened sediments downhill from the Tharsis rise, while the south-east flank encounters the high-friction zone of the elevated pre-sediment basement which inhibits its spread. Result: a lopsided volcano. The sediments beneath forming the low-friction basal zone beneath Olympus Mons would need to be good at retaining water, making clays the obvious candidates, and the authors note that the spectral signatures of clay materials have been detected by the Mars Express OMEGA imaging spectrometer.

In the last, four-sentence, paragraph of the paper the authors suggest that ‘[these] results have implications for extant life on Mars’. The erupted lavas of Olympus Mons could have trapped a water reservoir in the sediments beneath: ‘This deep reservoir, warmed by geothermal gradients and magmatic heat and protected from adverse surface conditions, would be a favored environment for the development and maintenance of thermophilic organisms’. Hence the headline at Australia’s ABC Science today: ‘Martian volcano could shelter life’.

  • Patrick K. McGovern & Julia K. Morgan, ‘Volcanic spreading and lateral variations in the structure of Olympus Mons, Mars’, Geology, vol. 37, no. 2 (February 2009), pp. 139-142. [Link to abstract only]

Image: mosaic of Olympus Mons created with the medium-resolution black and white MDIM combined with a low resolution color image mosaic acquired on the 735 orbit of Viking 1 on 22 June 1978. Image Processing by Jody Swann/Tammy Becker/Alfred McEwen, using the PICS (Planetary Image Cartography System) image processing system developed at the U.S. Geological Survey in Flagstaff, Arizona (NASA/NSSDC image).

Volcanic spreading and lateral variations in structure of Olympus Mons, Mars – ScienceDaily, 3 February 2009
Martian volcano could shelter life – ABC Science, 11 February 2009

ESA – Mars Express – home page for the ESA Mars Express mission
Unravelling part of Olympus Mons’ geologic history – HiRISE High Resolution Imaging Science Experiment (University of Arizona)
Volcanic Geology of Mars – from Albert T. Hsui, University of Illinois (Urbana-Champaign)
Highest and lowest points on Mars – Geology.com (on Olympus Mons and the Hellas Impact Crater)
Olympus Mons – Mike Dunford at The Questionable Authority shows just how big Olympus Mons is

The Volcanism Blog


1. Mike - 11 February 2009

I don’t think I would have said “The largest volcano we know of in the Solar System”. The only places which are still really unknown are the gas giants, which likely have no solid surface.

2. volcanism - 11 February 2009

I’m sure you’re right, but I’m a cautious chap. We know of no larger, that’s for sure.

3. John - 10 March 2009

Absence of evidence is not evidence of absence.

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