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Friday, 11 November 2011

Torres del Paine

Found these amazing photos on Wikipedia -- both are from the Torres del Paine area of Patagonia.  The rock here is ofter referred to as "red granite" -- probably because so many photos are taken of this massif with the light of the evening sun shining on the summits!  I gather that the rock is actually quartz diorite.....

Nothing at all to do with Stonehenge.  But apart from wanting to share these wonderful images, it's worth making the point that in some circumstances (such as these) ice seems to be capable of downcutting vertically with virtually no horizontal widening of the trough being cut.  Why is this?  Nobody is quite sure, but it seems that the processes of subglacial erosion are sometimes so effective that the rate of downcutting simply outstrips the frost-shattering and rockfall processes operating above the ice surface.  So the glaciers responsible for the erosion of this landscape much have been very dynamic indeed.  If you double click on the top photo, and look at the area left of centre, you can see a trough which is almost "clean" -- ie devoid of the very large morainic or scree accumulations which often mask the rock floors of troughs.  look at the magnificent ice-smoothed rock surfaces.  There are just a few perennial snowpatches left in these troughs flanking the peaks -- the glaciers that cut them have melted away completely.

5 comments:

Constantinos Ragazas said...

Brian,

Beautiful pictures! Thanks for sharing! Allow me to brainstorm a bit over them!

These are mountains in the photos, right? If so, the question is what geological process could account for their very erratic and irregular masses. You argue it was glacier erosion cutting and shaping these mountains. Just like glaciers can shape valleys. But its hard to see how advancing and retreating glaciers could leave such sharp edges and fissures and irregular outlines in rock solid mountains. And without any moraine debris at the base.

Here is a thought. How would mountains form beneath a very thick crust of solid ice, as compared to an ocean floor? Could the melting of the ice crust cover (several miles thick) result in the cooling of igneous intrusions to shape these mountains in such irregular masses?

Kostas

BRIAN JOHN said...

Kostas

Please think about James Hutton and the Principle of Uniformitarianism. My post here refers to it:

http://brian-mountainman.blogspot.com/2011/01/uniformitarianism-and-occams-razor.html

All you need to make a knife-edged or serrated rige with spectacular pillars and peaks is two glacial troughs side by side, and gradually widening until the intervening ridge is cut away. Simple!

Thick crust of solid ice? Well, of course this area, like much of the southern Andes, was heavily inundated by ice during the big glacial episodes. The ice sheet is sometimes referred to as the Cordilleran Ice Sheet -- it was big and thick -- and many of the big troughs like those at Torres del Paine were cut for the most part during these episodes.

Anonymous said...

I cannot believe that I shall be doing this but sometimes gargantuan misconceptions cry out to heaven for vengeance and in order to clear the air (wait for it).
The rocks are granite/granodiorite so we know that they coarse-grained so they must have cooled slowly and at a minimum depth of 5km but more than likely tens of kms. In igneous rocks all other things being equal grain size is related to cooling time controlled by ambient temp (equals depth)- the geothermal gradient.
The thermal blanket needs to be efficient hence needs to be rock- water whether solid or liquid is about as opposite that requirement as is possible-perhaps Olive Oil or spinach juice would be worse. Cooling time is of the order 100000 to tens of millions of years.

Last year we all saw what happens when you put magma directly beneath cold water/ice- you get plane-free/aplaner skies- stranded passengers and spectacular Icelandic sunsets.

The Greeks had words and concepts to spare (sparagmos is my favourite but too infrequently applied these days); our Kostas has but one misshapen idea but in some bizarre parallel universe what if he were correct. It is, however, Not this one, on to your next sir.
Cold explanations for barchans and Seif dunes perhaps

Thomas Rhymer.

BRIAN JOHN said...

My poetic friend -- thank you for the extra info. It's strange how people get their geological timescales all screwed up. just last night I was reading a book in which the author considered the bone caves of the Gower. He thought he was representing the literature correctly and expressed amazement that in the limestone bone caves there was evidence of interglacial fauna including hippos, cold climate fauna including woolly mammoth, and warm and wonderful coral seas! It hadn't occurred to him that the coral seas were over 300 million years ago, and that the bones in the cave were rather more recent!

That all goes to show that EVERYBODY, as part of a liberal education, should be forced to study geology, geomorphology and glaciology from an early age. The world would then be a much happier place.

Constantinos Ragazas said...

Thomas Rhymer,

It is not my intention ever to engage in 'sparagmos' of truth!
At the very top of my comment I characterized it as 'brainstorming'! It was intentional. And your comment was the reason.

Thank you for sharing …

Kostas