Guest post by Steven Goddard
Scientific American has reported that global warming may cause an increase in volcanic eruptions, due to increased magma formation at lower pressures as glaciers melt.
This caught my attention because I used to work as a volcano researcher and igneous petrologist.
That report said that about 10 percent of Iceland’s biggest ice cap, Vatnajokull, has melted since 1890 and the land nearby was rising about 25 millimetres (0.98 inch) a year, bringing shifts in geological stresses.
They estimated that the thaw had led to the formation of 1.4 cubic km (0.3 cubic mile) of magma deep below ground over the past century.
At high pressures such as under an ice cap, they reckon that rocks cannot expand to turn into liquid magma even if they are hot enough. “As the ice melts the rock can melt because the pressure decreases,” she said. Sigmundsson said that monitoring of the Vatnajokull volcano since 2008 suggested that the 2008 estimate for magma generation was “probably a minimum estimate. It can be somewhat larger.”
Interesting theory, but does it work quantitatively? Magmas, as with most solids, do show a direct relationship between the melting point and pressure. As the pressure increases, so does the melting point. (Ice is a noticeable exception to this, and shows an inverse relationship. The reason that people can ice skate is because the pressure under the blade creates a thin later of melted ice which lubricates the surface.
Below is a phase diagram of a basaltic magma similar to that found in Iceland, showing the relationship between temperature and pressure. The melting temperature does decrease at lower pressures. From 100 km depth to 0 km the melting point drops about 300°C. That is about 3°C / km. Ice is about one third as dense as basaltic magma, so the loss of 1 km of ice lowers the melting point by about 1C, or less than 0.1%.
More precisely, this study from the Carnegie Geophysical Institute did an empirical measurement of the relationship for one basaltic mineral – diposide. They found the relationship to be
Tm = 1391.5 + 0.01297 * P
Where Tm is the melting point in degrees C and P is the pressure in atmospheres. One atmosphere pressure is equal to about 10 metres of ice, so one additional metre of ice increases the melting point by about 0.0013°C. The loss of 100 metres of ice would therefore lower the melting point by about one tenth of a degree. The thickest ice in Iceland is only 500 meters thick, so complete loss of all ice would only alter the melting point by about 0.5°C, or less than 0.05%.
The geothermal gradient of the earth is typically about 40°C per km, so a 0.5°C change in temperature is equivalent to a depth change of about 20 metres. Near mid-ocean ridges this gradient is steeper, so the equivalent depth change in Iceland would be less than 20 metres. Is it credible that a 0.5°C decrease in the melting point could stimulate excess volcanic activity? Short answer – no. Volcanic activity is caused by magma rising to the surface, not glaciers melting. However, the loss of the glaciers would reduce the amount of steam and ash generated. Ash is formed when magma is cooled and fractured by steam. So the loss of the glaciers would reduce the size of the steam/ash cloud and make the Iceland volcanoes behave more like Hawaii volcanoes.
In short, the loss of all ice in Iceland would make the volcanoes less destructive.
BTW – On Al Gore’s planet, the geothermal gradient is much higher, with core temperatures averaging millions of degrees.
http://www.youtube.com/watch?v=ag2AWst3Qv4
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Steve says “This caught my attention because I used to work as a volcano researcher and igneous petrologist.”
hmmmm….my next book will be a romantic novel about a traveling volcanologist named Steve who is called in to calm the nerves of jittery EU air travelers….I’m thinking of calling it “Return to Reykjavík”.
Nice job, Steve, as always! Thanks!
This Precautionary Principle is a European invention and you are absolutely correct Doug that is exactly what it is. The only difficulty with the thing is the criteria is not well articulated or defined.
I really hope this thing cools off before next Friday as my sister is due to fly out of the UK then. Come on Icelanders, do your ’70’s trick.
OT, but with the number of eruptions and earthquakes sticking around the world recently, today, Adelaide, South Australia, experienced a magnitude 3.8 quake today. Strangely enough, Australia is one of the most geologically stable land masses on earth.
I knew what they were saying was theorhetically correct but not realistic. Thanks for the analysis Steven, and for providing the facts to confirm my suspicions.
Well done Steven. I think that settles the melting-point question.
I admit I only skimmed the SA piece, but the general idea that melting ice sheets might lead to increased volcanism struck me as credible not because of this factor but because of isostatic rebound and its effect on already-volatile regions such as seams between tectonic plates. Melting ice sheets would be like removing compression bandages from unhealed wounds (a naive metaphor, but you get the idea).
I realise that isostatic rebound is a very slow process, taking place over 100’s of years. Do you have a take on the types and magnitudes of the forces involved at how they compare to the orders required to trigger volcanism in such regions?
Responding to Wren: “Maybe, unless the MWP wasn’t very W.”
Even the AGW alarmists concede a regional MWP that affected Europe and Greenland. Maybe it skipped over Iceland.
Here’s the original paper from GRL on glacier retreat and volcanic activity in Iceland:
http://homepages.see.leeds.ac.uk/~earcpa/2008GL033510.pdf
It’s always better to critique the paper itself, rather than a press release.
In essence, the subsurface pressure changes caused by ice melt (equivalent to the loss of 5 cm of rock per year) are the same order of magnitude as the normal mantle upwelling rate beneath Iceland (1-10cm/yr).
Magma production increases with the upwelling rate. So the current rates of ice loss would be expected to increase the rate of magma production (in the area under the ice) anywhere from 500% to 50%- a pretty significant increase, IMO.
Actually this is too silly to reply to. It is Voodoo science in the extreme. If one thinks that glaciers have any impact on tectonic vulcanism at all, then they need to check themselves in at the home. And Iceland is ‘blessed’ with not only a very active moving plate or ridge, but a continuing shallow hot spot allowing for the more familiar conic activity.
Steve: Correction needed!
“…one basaltic mineral – diposide….” I think you mean: diopside.
Otherwise, good article. Where are these “geologists” making these ridiculous claims coming from? They are as pathetic as Eric what’s-his-name from U. Washington.
Put this another way and one could say that, according to the S. A. article, if/when the earth goes through another ice age, will much of the world volcanism cease? Are volcanoes an interglacial phenomena. I used to love Scientific American, now I have a hard time trusting any of it because of the high B.S. factor. Anybody know another good science magazine that has a little integrity left?
Once the ice, which yields water which yields steam which imparts an explosive dimension to these eruptions, is gone, these volcanoes should revert to something like Kilauea – very little ash production.
Another place where ice could pose a problem in relation to volcanism is Mt. Rainier. If that volcano resumes activity (it’s only dormant) the glacier covering the upper portion of the mountain could rapidly melt, posing a threat of catastrophic flooding and mud flows in a heavily populated area. The potential for destruction of property and life is high.
Mike Odin – Spot on, sir. Spot on! 😀
When I read this article earlier this week (linked elsewhere) my jaw dropped. Scientific American lost their patina of respectability as a scientific publication decades ago. Now they are trying to compete with Art Bell’s “Coast To Coast” with George Noory?
When will Richard C. Hoagland appear on the cover?
“The economic damage now being inflicted by the
volcano ash upon the British and European economies
appears to be on a scale equivalent to the
economic damage recently inflicted upon Iceland
by the activities of UK and Europe.”
…The financial crisis in Iceland was brought upon itself mainly by three Icelandic billionaires who all face criminal prosecutions. They colluded with Icelandic banks which had access to cheap international money markets mainly based in London and Europe. When international interest rates went up due to the massive mortgage scam in the U.S., the Icelandic banks could not cover their loan repayments, so they attempted to recover their losses by calling in the loans made to these billionaires, amongst others. The billionaires and some other big borrowers defaulted on their loans because they had gone on a gigantic spending spree, creating their empires of various companies bought with all this hot money and they didn’t have the cash, which in turn triggered the banks themselves to default on their loans to British and European banks. If that is what you call “inflicting damage on Iceland” then that is your interpretation. The damage inflicted by Iceland on the British banks which lent them the money in the first place, and through them the British economy has yet to be calculated. In the meantime, we would like our money back.
Pearland Aggie (20:51:23) :
Here is a good explanation and experiment from Argonne National Lab which demonstrates the melting of ice under pressure.
http://www.newton.dep.anl.gov/askasci/gen99/gen99523.htm
The link you provided assumes that pressure is equally applied under the skate, which is incorrect. The ice surface is rough, so the pressure on individual ice crystals is much higher.
Ice gets much less slippery at lower temperatures.
Steve Goddard, you may want to include the following paper in your post:
http://www.evropusamvinna.is/Apps/WebObjects/HI.woa/swdocument/1015721/Sturkell_etal_2009b.pdf
In it the seasonal seismicity and its potential relation to water pore pressure above a magmatic chamber is described. Clearly the “alarmist” stuff might be an extension of a local observed phenomenon in order to conveniently link an icelandic eruption to global warming and milk it.
Re closures of commercial (and military) flights:
http://www.metoffice.gov.uk/aviation/vaac/vaacuk_vag.html
Graphics update every 6 hours or so.
German combat troops in Afghanistan have been told not to get shot because (at least for now), they can only be casevac’ed to Istambul. So (according to Deutsche Welle) they’ve retreated to barracks, along with others. Instead of making arrangements to casevac to/via alternates like Perth (Western Australia) via DXB. I know that it’s more than twice as far but you can make the distance.
No no no no no.
This is a variation on the “Katrina was a devastating hurricane, therefore global warming causes more hurricanes” meme.
It is also the meme that everything that can possibly be even remotely associated with global warming is fair game to be tagged “due to global warming.” The scientists all have seen a lot of money flowing to people who can tie their work to AGW well enough, so hell, why shouldn’t they try? Funding is funding, right?
Anthony, you referred to it as a “theory.” If I might say, this is just a speculation, not a “theory.” Just because a “scientist” throws an idea out there doesn’t give it status as a theory. The entire golobal warming theory has quite a bit of evidence behind it even while it also has a lot of evidence against it. This thing just popped up, so it has a long way to go before it can be called a theory.
The last I heard, Scientific American is news media, not a scientific peer-reviewed journal. Scientists have NO business throwing even well-thought-out ideas out to the news media before they’ve put the idea through several of the rigors of scientific inquiry. That is what got Pons and Fleischman in so much trouble in 1989. The speculation of the moment does not make a theory. At best, it is a hypothesis.
If the water were gone, it is true the volcano would have far less ash propulsion. But i do not believe it will be anything like Kilauea. It has a far higher silica content because that is the nature of tectonic plates. Kilauea does not have such. Then this is a rift eruption, which mean it is not generally conic but lateral. This causes additional problems. Bad ones. Let me cite an example. Loihi is under a great deal of water. 9000 feet off of Hawaii. While water inundates it, that water has virtually no effect on the vulcanism or the make up of ash. The pressure of the water is likely heavier than this glacier. The depth of the magma source for Hawaii volcanoes makes Hawaii a relatively benign volcanic erupter, although the water and silica of sufficient concentration (under other circumstances are explosive. In the Hawaii instance, as I understand it, water only serves to encourage solidification and channelization. Iceland has rift eruptions with silica and water. In many respects this is far more dangerous.
Waking up this morning in southern England, I can see and taste the dust from the unpronounceable Icelandic volcano. We also had some global cooling overnight, 1decC this morning. Everyone is coughing too.
Wow, an adiabatic lapse rate for basalt. Whoda thunkit? And wet/dry versions, too.
>>hmmmm….my next book will be a romantic novel about a
>>traveling volcanologist named Steve who is called in to calm
>>the nerves of jittery EU air travelers….I’m thinking of calling it
>>“Return to Reykjavík”.
Will he carry a red hanky?? 😉
On a more serious note, does the pressure of the ice on the surface seal up more potential vents? – so will the melting ice weaken the surface and open up the area to much more vucanism??
.
>>I’m not sure melting point has a lot to do with it.
Surely it is the outgassing pressure in the magma that is critical here (whatever name this critical pressure has).
The magma behaves like a soda bottle, and with sufficient pressure on the soda it is stable. Release that pressure, and suddenly it effervesces and “boils” up all over the place.
.
Ah, so that’s why the nearby Katla erupted in 1580, 1612, 1625, 1660, 1721, 1755, 1823, 1860 and 1918.
Step 1: Invent Global Warming
Step2: Blame anything “current” on Global Warming
Step3: Tax, Tax, TAX!!!!