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Author Topic: AGW induced tectonic activity -- glacial rebound, glacial isostatic adjustment  (Read 6264 times)

lisa

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It makes sense to me that the mantle of the earth would have to shrug and settle as it adjusts to mass changes from melting ice.  I'd think the faster we lose ice from the Antarctica and Greenland, the more abrupt those shrugs might be. 
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<a href="http://www.sciencedirect.com/science/article/pii/S0012821X13007036">The effect of earth rheology and ice-sheet size on fault slip and magnitude of postglacial earthquakes</a>(Steffan, et al., 2014) models what those mantle adjustments might look like.

I always figured that when the ice flowed of Antarctica, it would pop up like a piece of toast. 

Not quite, but the paper concludes:

Quote
The answers to the questions raised in the Introduction are summarized below:

•Although the size of the ice sheet might not have a large influence on the fault throw, it affects the activation time by several thousands of years as horizontal rebound stresses increase with a decrease in width.

•Estimated fault throws in North America and Europe do not constrain ice-sheet thicknesses, because predicted fault throw varies by only a few cm for a change in the ice thickness expected for these regions.

•The earth model parameters have only a small effect on fault throw and activation time, except for the crustal stiffness and lithospheric thicknesses, which change the throw by about 3 m.

•Even 60° dipping faults can be activated as a reverse fault, and if activated, they may generate large magnitude earthquake events.

I think the earth will see some rather dramatic quakes by the end of the century.

folke_kelm

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"I think the earth will see some rather dramatic quakes by the end of the century"

No, not even remote as fast. First you have to remove most oft the ice, then you will have the isostatic rebound of the crust and the mantle.
Here in Sweden we still feel earth quakes from this mechanism and the crust is still rising with up to 4 cm a year, so it is a very slow process.

Another mechanism, which in my opinion is more serious, is melting of magma due to pressure release. All hot magma from below is originaly transported as "solid" rock up to a distinct border when it melts. The melting point of rock is strong pressure related, less pressure means lower melting point. Hot mantle material will melt emediately, when the ice is removed, when it is exactly at the border of melting conditions.
Pressure release due to melting ice is a rather fast mechanism, capable to induce melt of otherwise not melting mantle or crustmaterial. And then booom......

AbruptSLR

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If the sea level goes up 2 or more meters by 2100 then the extra weight of the ocean will change the pressure distribution on faults & volcanoes.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Laurent

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Is it possible that the heat that is stored in the oceans will increase the heat in the mantle because the energy that was transfered from the mantle to the oceans will be diminished so it should build up heat also in the mantle ?

lisa

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re #2 - redistribution of weight --

Yeah, that's what I was thinking.  I can see that the rebound would take a long time, but the redistribution of all that water weight is also what I was thinking about -- that even thought the rebound is a slow process, it just seems that the sudden loss of the weight of ice in Antarctica would have a dramatic effect on the fault lines.

AbruptSLR

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re #2 - redistribution of weight --

Yeah, that's what I was thinking.  I can see that the rebound would take a long time, but the redistribution of all that water weight is also what I was thinking about -- that even thought the rebound is a slow process, it just seems that the sudden loss of the weight of ice in Antarctica would have a dramatic effect on the fault lines.

You might want to take a look at the following thread in the Antarctic folder:

http://forum.arctic-sea-ice.net/index.php/topic,393.0.html
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johnm33

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Lisa take a look at 'Earth in upheaval' by Velikovsky chapter vi skip to Tiahuanaco in the Andes where he presents evidence of dramatic recent upheavals.

sidd

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I do not think that Velikovsky is credible.

lisa

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"A powerful earthquake struck Nepal Saturday, killing at least 906 people across a swath of four countries as the violently shaking earth collapsed houses, leveled centuries-old temples and triggered avalanches on Mt. Everest. It was the worst tremor to hit the poor South Asian nation in over 80 years....

A magnitude-6.6 aftershock hit about an hour later, and smaller aftershocks continued to jolt the region for hours. Residents ran out of homes and buildings in panic. Walls tumbled, large cracks opened up on streets and walls. Towers collapsed and clouds of dust began to swirl all around....

A mountaineering guide, Ang Tshering, said an avalanche swept the face of Mt. Everest after the earthquake, and government officials said at least 8 climbers were killed and 30 injured. Their nationalities were not immediately known."

The epicenter of the quake was about 50 miles northwest of Katmandu, according to the U.S. Geological Survey, which revised the magnitude of the quake down to 7.8 from an earlier estimate of 7.9.

http://www.msn.com/en-us/news/world/nepal-quake-hundreds-dead-history-crumbled-everest-shaken/ar-BBiEIdv?ocid=UP97DHP

plinius

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That's the usual quake that happens every ~100 years there. India's crashing into Asia has really nothing to do with our CO2 emissions...

lisa

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Granted.  But I do wonder if the changing weight of oceans and continents as ice melts and oceans increase will effect even plate tectonics.  It seems to me that it's all connected. 

plinius

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I am not aware of any reports of a catastrophe when the Mediterranean filled up again, which was probably the most catastrophic mass redistribution event in "modern" geologic history. And apart from some mild changes in volcanism of some areas (wasn't there something with Canada?) there should not be major issues with geology, apart from height changes (which are very worrying for coastal cities.) Remember that major quakes are caused by plates in friction, chiefly subduction zones. If you just do isostatic adjustment, the plates are quite fine.

Gray-Wolf

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Do we not have some major movement of 'old faults' at the end of the last glaciation in the far NW of Europe?

If the weight of ice causes different level of depression either side of the existing fault then unloading might lead to the surface sorting itself out again via a 'one off' event as the fault snaps back into it's old positioning before the weight of ice altered it?
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folke_kelm

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Grey wolf,

There are still movements of old faults in the north of europe, most quakes in Scandinavia are related to unloading and isostatic rebound. But these movements and earth quakes are absolutely not major movements, only very moderate.
It is very tiny compared to major strike slip faults with offset of 10s of meters in one single movement or adding up elastic strain from 10 or more cm plate movement a year.
strong earthquakes result almost entirely from horizontal stress and plate movement, while climate change is only able to provide vertical stress at distinct places.

Lisa,
"But I do wonder if the changing weight of oceans and continents as ice melts and oceans increase will effect even plate tectonics.  It seems to me that it's all connected."

Please read some textbook about plate tectonics. It is all about horizontal movement and the force to move plates is so huge compared to the additional weight of increased ocean level (a static stress) that it will not recognise it at all. You must always think about in which direction a plate is moving or forced to move. A possible result of adding vertical stress to a horizontal movement may be a reduction in frequancy of quakes which will be stronger then, or an increase in frequency, but then the quakes will have less magnitude. Most likely you will not see any influence at all.
Attributing climate change to tectonic earthquakes is a very very long shot, hitting right nearly impossible.

lisa

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Thank you, folke_kelm.  I'll do some reading.