Mountain Roots and Crust Stabilisation

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Mountain Roots and Crust Stabilisation

#1  Postby Ciwan » Jan 25, 2012 8:29 am

Hello Friends

I have a question on Geology, and I hope someone can help me understand. :ask:

I always thought the Earth's crust was stabilized (needs stabilizing since it is basically floating on Magma) by the nearly-uniform-equal pull of Gravity from all sides.

Yet, a few days back I heard that mountains play a role in stabilizing the Earth's crust ! and I can't see how :( I have read this article, and love the bit about the so called 'roots' of a mountain ... I totally get that (awesome analogy with ice bergs, though I don't think 'roots' is a good name).

But in that article I can't see how the mountains and their underside help in stabilizing the Earth's crust !! Or have I missed something ?

I would greatly appreciate some help in understanding this. Think of me as a baby, so please try and explain it super clearly :oops: I'm not good with jargon.

Thank You.
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Re: Mountain Roots and Crust Stabilisation

#2  Postby z8000783 » Jan 25, 2012 12:48 pm

You were probably looking at a Muslim article of some sort. Muslims frequently quote part of the Quran that says this:
Quran wrote:[78:6] Did we not make the earth habitable?
[78:7] And the mountains stabilizers (pegs)?

You are correct, the crustal plates move and when two plates of similar density collide the result is an upthrust and a down thrust at that point, in other words the crust becomes thicker therefor example the Himalayas where the Indian plate meets the Eurasian plate. Where plates are of different densities one is subducted under the other usually forming a deep trench when under the ocean.

I am not sure what you mean by ‘needs stabilising’, the tectonics place nor the Earth's could don't care if they are stable or not, but the short answer they can still be unstable i.e. liable the earthquakes. Of course, volcanoes which are also mountains, are created by an entirely different process and have no ‘roots’ but they always seem to be glossed over.

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Re: Mountain Roots and Crust Stabilisation

#3  Postby Ciwan » Jan 25, 2012 12:56 pm

Good point about the Volcanoes. And yes It was a Muslim site/video. :D

So you're saying the Crust would still be stable even without the Mountains ? And the mountains play no role in the stabilization of Earth's crust ?

Or am I confusing things, since 'stable' has no meaning here ? In the video, the guy was saying that without the mountains (pegs) the earth's crust would keep piling on top of one another and keep moving around like a very thick soup !! (not his exact words, but his hand movements suggested something of that nature lol).

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Re: Mountain Roots and Crust Stabilisation

#4  Postby z8000783 » Jan 25, 2012 12:59 pm

You need to explain what you mean by stabilisation. What would you expect to see in the areas where the crust us 'unstable'?

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Re: Mountain Roots and Crust Stabilisation

#5  Postby Ciwan » Jan 25, 2012 1:02 pm

Let's say there were no mountains on Earth, and it was all flat ground (talking about the stuff above sea level) .... How would that affect Earth's crust overall ?

Also ignoring the role mountains play in creating rain and desserts.
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Re: Mountain Roots and Crust Stabilisation

#6  Postby Spearthrower » Jan 25, 2012 1:06 pm

Ciwan wrote:
I always thought the Earth's crust was stabilized (needs stabilizing since it is basically floating on Magma) by the nearly-uniform-equal pull of Gravity from all sides.


The crust is not floating on magma, nor is it really floating on anything.

The layer underneath the crust is called the upper mantle, and it is predominantly solid and rigid. The crust needs stabilising like the skin on an apple needs stabilising! :)
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Re: Mountain Roots and Crust Stabilisation

#7  Postby Spearthrower » Jan 25, 2012 1:08 pm

Ciwan wrote:Good point about the Volcanoes. And yes It was a Muslim site/video. :D

So you're saying the Crust would still be stable even without the Mountains ? And the mountains play no role in the stabilization of Earth's crust ?

Or am I confusing things, since 'stable' has no meaning here ? In the video, the guy was saying that without the mountains (pegs) the earth's crust would keep piling on top of one another and keep moving around like a very thick soup !! (not his exact words, but his hand movements suggested something of that nature lol).

Thanks



The mountains ARE the earth's crust, so his explanation is not even wrong, as is to be expected.

And the crust does keep moving around and piling on top of itself: these are called mountains! :grin:

Folding and blocking are two of the three types of mountain formation, the other being volcanoes.
Last edited by Spearthrower on Jan 25, 2012 1:10 pm, edited 1 time in total.
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Re: Mountain Roots and Crust Stabilisation

#8  Postby Ciwan » Jan 25, 2012 1:10 pm

LOL Thanks SpearThrower !! So Mountains play no role at all ?

And in Volcano Formation, how is it that Magma (runny) flows up the volcano if underneath the crust is another layer that is 'solid and rigid' ! is it because that magma comes from even a further layer down ?

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Re: Mountain Roots and Crust Stabilisation

#9  Postby Spearthrower » Jan 25, 2012 1:12 pm

Ciwan wrote:LOL Thanks SpearThrower !! So Mountains play no role at all ?


Mountains are the effect of this motion, not a preventative measure against it.


Ciwan wrote:And in Volcano Formation, how is it that Magma (runny) flows up the volcano if underneath the crust is another layer that is 'solid and rigid' ! is it because that magma comes from even a further layer down ?

Thanks


When the temperature and pressure conditions push rock into a molten state, then magma forms - it forms both in the mantle and in the crust.
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Re: Mountain Roots and Crust Stabilisation

#10  Postby Ciwan » Jan 25, 2012 1:15 pm

Spearthrower wrote:When the temperature and pressure conditions push rock into a molten state, then magma forms - it forms both in the mantle and in the crust.


Nice, Thank You.

Another Q. Why would Pressure by so high to Melt Rock near the Crust ? Considering there isn't too much weight above it ?
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Re: Mountain Roots and Crust Stabilisation

#11  Postby Spearthrower » Jan 25, 2012 1:26 pm

Ciwan wrote:
Spearthrower wrote:When the temperature and pressure conditions push rock into a molten state, then magma forms - it forms both in the mantle and in the crust.


Nice, Thank You.

Another Q. Why would Pressure by so high to Melt Rock near the Crust ? Considering there isn't too much weight above it ?



It's actually not high pressure, but decompression - a decrease in pressure. The temperature below which rocks are completely solid (called solidus temperature) increases with increasing pressure (i.e. at greater pressure, rocks need to be comparatively hotter to be in a liquid state). So as some of the mantle moves up to an area of lower pressure, the reduction in pressure makes the rock melt, although its at exactly the same temperature, leading to magma formation.

If you need solidus and liquidus state transitions explained though, you're going to need to ask a chemist as it goes beyond my knowledge - I just know it is, rather than how it is! :grin:
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Re: Mountain Roots and Crust Stabilisation

#12  Postby z8000783 » Jan 25, 2012 1:29 pm

Have a look here -

[youtube]http://www.youtube.com/watch?v=Bf4iJvrAv-M[/youtube]

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Re: Mountain Roots and Crust Stabilisation

#13  Postby Ciwan » Jan 25, 2012 1:30 pm

Fascinating ! But doesn't the area of lower pressure also have lower temperature ? so we're back where we started ? no ?

Nice video, I knew most of what was in it already, but I want the specifics :grin: Like my Q above ? Or is my Q stupid ? if Yes .. please explain why.
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Re: Mountain Roots and Crust Stabilisation

#14  Postby Spearthrower » Jan 25, 2012 1:39 pm

Ciwan wrote:Fascinating ! But doesn't the area of lower pressure also have lower temperature ? so we're back where we started ? no ?


Once it moves into the lower pressure area the temperature it needs to be in order to become liquid is much, much lower. The heat from the rock has nowhere to go and heat doesn't instantly dissipate anyway. It turns into magma long before it cools sufficiently to turn back into solid rock - you see lava managing to remain a viscous liquid both on the surface and in the sea!
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Re: Mountain Roots and Crust Stabilisation

#15  Postby Ciwan » Jan 25, 2012 1:40 pm

Awesome, that's more like it. Thank You Very Much both of you. :cheers:
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Re: Mountain Roots and Crust Stabilisation

#16  Postby Spearthrower » Jan 25, 2012 1:52 pm

Ciwan wrote:Awesome, that's more like it. Thank You Very Much both of you. :cheers:


That's alright - I am sure there are experts who could pick at some of my explanations, but even if my description is not 100% correct, it's far closer than the nonsense asserted by apologists trying to retrofit the contents of their holy book to make it look as if it had modern scientific understanding.
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Re: Mountain Roots and Crust Stabilisation

#17  Postby halucigenia » Jan 25, 2012 2:10 pm

Ciwan wrote:
Spearthrower wrote:When the temperature and pressure conditions push rock into a molten state, then magma forms - it forms both in the mantle and in the crust.


Nice, Thank You.

Another Q. Why would Pressure by so high to Melt Rock near the Crust ? Considering there isn't too much weight above it ?

Considering the depth of continental rock is 30-50Km this ammount of weight produces very great pressures.
However, the heat coming from the mantle due to convection is what generally melts crustal rocks.
Magma is generally produced at subduction zones where the oceanic plates are subducted into the mantle and also where heat "plumes" from the mantle transfer heat into the crustal rocks.
Subduction zones produce the arcs of volcanoes at the plate margins and mantle plumes produce mid oceanic islands like Hawaii.
Mantle plumes underneath continents produce volcanic areas like Yellowstone in the US and rifting like in East Africa.

Melts from oceanic crust and continental crust produce different types of rock and the associated vulcanism is different too. Oceanic plumes produce runny basaltic magma that produces effusive eruptions producing basaltic rock and melting of continental crust generally produces more viscous magma which tends to erupt more violently producing explosive eruptions. Fine grained rocks called rhyolite are produced from rapidly cooling magma produced from melted continental crust.

As for the OP about mountains "stabilising" the earth's crust I can't for the life of me understand what this assertion is referring to - is it simply an ad hock attempt at justification of passages in the Koran? :what:
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Re: Mountain Roots and Crust Stabilisation

#18  Postby Ciwan » Jan 25, 2012 7:19 pm

Awesome ! Thank You for the informative post Halucigenia.

About the original post, the muslim guy was saying that Allah placed the mountains as Pegs to stabilise the surface of the earth !! Not sure exactly what that means though and I'm guessing neither does he.
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Re: Mountain Roots and Crust Stabilisation

#19  Postby Spearthrower » Jan 25, 2012 8:00 pm

Ciwan wrote:Awesome ! Thank You for the informative post Halucigenia.

About the original post, the muslim guy was saying that Allah placed the mountains as Pegs to stabilise the surface of the earth !! Not sure exactly what that means though and I'm guessing neither does he.


Yeah, he read it in the Koran so it must be true, and it's certain that science supports it, and if contemporary science doesn't, then it will do when it find out. Typical nonsense apologetics.
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Re: Mountain Roots and Crust Stabilisation

#20  Postby halucigenia » Jan 26, 2012 11:07 am

Ciwan wrote:Awesome ! Thank You for the informative post Halucigenia.
Thank you. I hoped that it would answer your questions. It was just a quick sketch and there is a whole lot more I could tell you about igneous geology if you have any more specific questions. I also just realised that I left out an important part about how the oceanic crust forms at mid ocean ridges that would be the other main source of magmatic activity, but that would probably not be in direct answer to your question about crustal melting. It is, however, an important part of the process as it is the origin of crustal material.

Ciwan wrote:About the original post, the muslim guy was saying that Allah placed the mountains as Pegs to stabilise the surface of the earth !! Not sure exactly what that means though and I'm guessing neither does he.
I expect that you were directed to the page in the OP answering the question When did we first find out that mountains had roots and that these mountains stabilised the earth? by a a Muslim fundie with the assertion that modern science only recently found the answer but the writers of Koran knew about this long before then. :rolleyes:
I also suspect that the question was originally asked of the Geological Society by a Muslim fundie expressly for this purpose.
That page is an excellent answer to the first part of the question "When did we first find out that mountains had roots" but in no way shows that the second part "and that these mountains stabilised the earth" is even meaningful and therefore cannot justifiably be used by Muslim fundies in the way I suspect that it is repeatedly used by them. :rolleyes:
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