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Rockaholic Adventures

Rockaholic Adventures is the place for conversation and discussion about geologic phenomena and mountaineering excursions. You'll also read reviews written from the perspective of today's technologically-advanced outdoorsman - one with a background in engineering and geology.

Rockaholic Adventures also covers topics such as unconventional oil & gas technologies and environmental geochemistry. The blog's owner, Shawn, is a technical writer at IHS where he writes a quarterly newsletter, Unconventional Oil & Gas News. He graduated magna cum laude in 2006 from the University at Albany where he majored in geology.

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Morphology of Olympus Mons

Posted December 05, 2016 2:42 PM by Shawn

After discussing the morphology of Olympus Mons I felt compelled to share my intuition of the shield volcanos existence and morphology strictly through a hypothetical approach. The shield volcano may often be compared to our largest terrestrial feature Mt. Everest due to its sheer size, but it’s believed to have more in common with Mauna Kea. It is in fact three times the height of Mt. Everest at 22km above Mars’ surface and exhibits the properties of a shield volcano.

A shield volcano is formed by a continuous convection of mafic magma that produces the volcano’s shield shape through continuous eruption of mafic rich lava. Although it is believed that plate tectonics exists on Mars I suggest that it is a dying planet and the vector velocity of any rigid plates would be minuscule. Furthermore the planet is lacking any great variance in plate densities. That is in contrast to our planet where plate tectonics evolves through the highly contrasting densities between oceanic and continental plates. In the absence of subduction complexes, stratovolcanoes, and spreading ridges we are left with a much more homogenous lithosphere. This theory led me to believe that Mauna Kea could rival Olympus Mons if the Pacific plate would stop moving and form a single feature rather than a chain of volcanic islands.

Secondly, there are a few phenomena regarding the morphology of Olympus Mons that may be hypothesized but as far as I understand poorly understood or explained for. The enlarged basal scarp circumventing the mountain and the enormous scalloped caldera are two features that are unrivaled in our terrestrial environment.

The enlarged basal scarp has baffled many as the dramatic elevation profile drops 7km, almost the full height of Mt. Everest. One theory suggests this may have been caused by glaciation but I’d like to entertain a phenomenon non-existent on earth.

Plausibly the enlarged lithosphere emanating from the epicenter of Olympus Mons fights gravity. Buoyancy may be induced by accretion of outer mantle material. As the connected lithosphere is pulled upwards by the large feature there exist strain and ultimately detachment and settlement. The basal scarp is then an area of localized strain and a fault in itself. Think of an iceberg connected to a thin ice sheet where only the iceberg grows in thickness causing detachment and settlement of the surrounding ice sheet.

Lastly I’ll attempt to explain the scalloped caldera. This I again attempt to contribute to the object being near stationary on the planet’s surface. There isn’t a satellite caldera or cone but rather and overlay of large massive calderas where each implosion is an overlay in succession time frames. New calderas are formed and exit through a path of least resistance. The size of these calderas dwarfs those known on Earth due to a greater resistance to extrusive lava flow by its increases height and volume of overburden. It would be more conducive to smaller calderas if flow began to exit through the side of the volcano as if it were part of a moving tectonic plate.

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Guru

Join Date: Jun 2007
Posts: 872
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#1

Re: Morphology of Olympus Mons

12/07/2016 11:23 AM

"... there are a few phenomena regarding the morphology of Olympus Mons that may be hypothesized but as far as I understand poorly understood or explained for."

I couldn't agree more ! "Poorly understood, as far as you understand."

"The enlarged basal scarp has baffled many..."

(Not-to-worry.... many things baffle MANY geologists... easily forgiven when the subject is 50 million+ kilometers away!)

"Plausibly the enlarged lithosphere emanating from the epicenter of Olympus Mons fights gravity."

Or , maybe . . . .

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Power-User

Join Date: Apr 2005
Location: Averill Park, NY
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#2
In reply to #1

Re: Morphology of Olympus Mons

12/07/2016 11:41 AM

That basal scarp is one interesting feature. I don't buy that glaciation has anything to do with its existence. I'd like to entertain another theory out there. I myself am largely convinced it is a fault. The hidden lava flows in the valley could be buried by the frequent sand storms and when is the last time that we could hypothesize mars being glaciated, outside its polar caps? ... This is the beautiful think about geology and plate tectonics... it is far from scientific law and most explanations are at best an accepted theory.

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Guru

Join Date: Dec 2016
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#3
In reply to #2

Re: Morphology of Olympus Mons

12/07/2016 1:10 PM

Was reading somewhere that O.M. formed as a result as a result of a (very) large asteroid impact at or near the opposite side of the planet?

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Guru

Join Date: Dec 2016
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#4

Re: Morphology of Olympus Mons

12/07/2016 11:42 PM

Hellas Planitia is antipodal to Alba Patera. It and the somewhat smaller Isidis Planitia together are roughly antipodal to the Tharsis Bulge, with its enormous shield volcanoes, while Argyre Planitia is roughly antipodal to Elysium, the other major uplifted region of shield volcanoes on Mars. It is not known whether the shield volcanoes were caused by antipodal impacts like that which produced Hellas, or if it is mere coincidence.

This is also an interesting take:

http://www.mantleplumes.org/DLABook/Hamilton2015.pdf

Discussion of Martian volcanism begins on page 24/35.

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Power-User

Join Date: Apr 2005
Location: Averill Park, NY
Posts: 253
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#5
In reply to #4

Re: Morphology of Olympus Mons

12/08/2016 10:47 AM

Mantle plumes forming antipodal to impact craters. Its an interesting theory, and my first instinction was to see what was antipodal to Mauna Kea, but to test this theory you would need a finite time interval for the suggested impact crater and accurate reconstruction of plate tectonics. Was a crater impact responsible for the destruction of Pangaea, the extinction of dinosaurs, and the consequent formation of the Hawaiin Ridge,? Did Mars ever possess active tectonics and why is the largest impact crater not antipodal to O.M.?

I think we both agree that O.M. is shield volcano, and this theory still does not explain the basal scarp. I did dig up a theory that mirrors my own though... At least in part. Uplift, however would be accompanied by normal faulting where the author here describes basal detachment and thrust faulting.

http://link.springer.com/referenceworkentry/10.1007/978-1-4614-9213-9_14-1

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