How could this pyramidal Mountain have been formed?
How could this pyramidal peak have been formed in Antarctica? Little is known about it as far as I know but what is known is that its miles away from any existing plate boundary and its shape is also highly atypical, hence I present the above question.
The question bases on two sub-questions really:
A) How did it form so far away from a plate boundary? B) How did it form in this unusual shape?
https://en.wikipedia.org/wiki/The_Pyramid_(Antarctica)
geology plate-tectonics glaciology mountains antarctic
Camilo Rada
Such forms tend to be created by glacial activity, which, ahem, the ice-covered continent is known for. Much discussion of this in the related question in Skeptics: Are there three pyramids in Antarctica?
Here's the generic answer in Wikipedia:
A pyramidal peak, sometimes in its most extreme form called a glacial horn, is an angular, sharply pointed mountain peak which results from the cirque erosion due to multiple glaciers diverging from a central point. It may be an example of a nunatak.
Here's a diagram of the formation process posted on Ace Geography:
Not knowing the specifics of the featured peak, as I understand it there are two general mechanisms of glacial erosion that apply:
Assume we begin with some sort of mounded terrain, or a relatively small protrusion on a larger continental surface like Antarctica. In a very cold environment, precipitation will fall as snow, mound up, and turn into ice. Generally, more ice will form on whatever side of the mound that is sheltered from sunlight (north slopes in the northern hemisphere, south slopes in the southern. Eventually the ice will move under its own weight, abrading the surface as it goes in a manner that will tend to exaggerate the original geometry of the mound. If the mound starts with or develops a slight dip in the slope, ice flowing off the back and side walls will dig a cirque or bowl. Depending on the starting conditions, your mound may develop several cirques; as ice grinds away at the lower elevations, you may wind up with a central, relatively slender peak with several ridges and valleys.
A second mechanism is having a glacier coming down a broader slope and cutting through an existing ridge. (Your ridgeline may begin with a triangular cross-section, or may have developed one from the glacial processes mentioned above.) At some point, ice from a higher elevation will flow across or through your ridgeline (just as a river would), eroding a gorge through the ridge.
Inevitably, given enough material to work from, and even with a relatively smooth starting surface, the erosive power of ice will give you steep slopes and some pyramidal structures.
jeffronicusjeffronicus
$\begingroup$ That doesn't explain why those mountains are much more common in Antarctica than anywhere else. See my answer below. $\endgroup$ – Camilo Rada Jan 29 '18 at 22:51
That mountain is mount Evans (3,950 m), located in the Sentinel Range in inner Antarctica (S 78.30698°, W 85.91698°), the highest mountain range in the continent.
(Map courtesy of @KeithMcClary see comments)
In general, geologic features become smoother by erosion (by water, glaciers or wind). These peaks are so high that there were never covered by glaciers and the area is so cold that liquid water almost doesn't exist. Therefore, there is no erosion by water (or freeze thaw cicles), neither the wind, because of the lack of dust/sand particles (the wind doesn't erode by itself, what do erode are the particle it carries). Consequently, those mountains are so sharp due to the lack of erosion. Take for example any rock: If you break it into pieces, those pieces will have sharp edges, with no erosion those sharp edges will persist. Similarly, at a larger scale, sharp ridges and edges on mountains can persist and withstand the pass of time.
This is me on mount Tyree camp one, during The Omega Foundation mapping expedition of 2005, mount Evans is in the background
Camilo RadaCamilo Rada
$\begingroup$ "These peaks are so high that there were never covered by glaciers"??? There are still glaciers at those altitudes and a lot higher in a lot of places in Earth. $\endgroup$ – Pere Jan 28 '18 at 18:16
$\begingroup$ @Pere Yes, there are glaciers, in the peaks that are less steep and can accumulate snow. Such is the case for Mount Vinson and Many others. But steep peaks as mount Evans do not accumulate snow and are not covered by glaciers as you can see. When I said that, I meant the big glaciers, the ice sheet the creep over Antarctica smoothing everything except the very top of the rock massifs that stay above the ice. Like Mount Evans. The ice surrounding those peaks is a few kilometers deep, and the rock under the ice is smoother that the sharp peaks we can see above. $\endgroup$ – Camilo Rada Jan 29 '18 at 1:12
$\begingroup$ Maybe you mean that there is no ice cap or ice sheet over mount Evans, or that it pokes through the surrounding ice field. However, please take in account that those aren't the only kind of glaciers, and that glacier erosion is notable at those altitudes. For example, one of the most known textbook example of glacier sculpted summit is the Matterhorn, about 500 m higher than mount Evans. Mount Evans and Matterhorn is so sharp due to erosion, not due to lack of erosion - even if in such erosion had been largely reduced in the last few thousands of years. $\endgroup$ – Pere Jan 29 '18 at 14:25
$\begingroup$ @Pere Yes that what I mean. And you can't compare Matterhorn with Evans, that is at latitude 86°. Despite it is a bit lower, it is way colder. And there there is no erosion by freeze-thaw . I'm aware of all kinds of glaciers (I'm a glaciologist), but Mount Evans is too steep on all side to form a glacier (you can see it have no glaciers on its walls). So that's why it have escaped all kinds of erosion basically. $\endgroup$ – Camilo Rada Jan 29 '18 at 22:48
$\begingroup$ I cut this image from an old USGS map (which doesn't show recently named peaks :>) ). Could you use it to illustrate your explanation? $\endgroup$ – Keith McClary Apr 13 '19 at 1:38
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