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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So, you admit, that if Gore is correct, we may have reached a tipping point?
Great last line. And very interesting analysis. Can the guy who was quoted on this scary story possibly not know this?
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.
This is simply a non-judgmental observation
unrelated to any karma or other
introspection.
I’m not sure melting point has a lot to do with it.
An eruption is caused by a molten or semi-molten blob of magma that has a lower density than the surrounding rock. As a result it rises and either intrudes into the country rock – creating dykes – or burst onto the surface creating different volcano forms depending on the chemical composition of the magma. In all cases it intrudes through already solid rock
Basaltic (basic) magmas are very fluid and have a lower melting point – hence they flow easily with long flat cone shapes.
Acidic magmas (high in SiO2) tend to produce smaller steeper cones as they freeze much more quickly.
Depending on the amount of ground water the magma passes through you get different effects such as cinder cones.
If you get a really energetic magma ball rising it can rise at incredible speed and create continent wide destruction from the resulting high energy release on hitting the surface – coming soon to a Yellowstone National Park near you.
If the theory were true, then the MWP would show us to have been awash in volcanoes, right?
I’m awaiting the pronouncement that the cooling resulting from this eruption will be more severe due to global warming. In fact, the cooling will not only be more severe, but will last longer as further testament to global warming.
–“Global Warming….We don’t make the weather, we make the weather worse”
I’d call that game, set, and match.
But will there be any letters to Anti-Scientific American to point this out?
Setting on several cubic meters of Columbia River Basalt, I know that this
Basaltic flow lasted a very long time. Basaltic Volcanoes seem to cook on and on
and this isn’t good for the rest of the northern hemisphere..
DJ Meredith (20:21:43) :
If the theory were true, then the MWP would show us to have been awash in volcanoes, right?
=====
Maybe, unless the MWP wasn’t very W.
“The fact is that we can’t account for the lack of warming at the moment and
it is a travesty that we can’t.” Trenberth to Mann, ClimateGate email:
=================================================
I’VE CRACKED THE CODE. What Tranberth was really saying was:
‘…….it’s a shame that we’ve taken this model and put lipstick on her, added a bit of plastic surgery, corsett to take away the MWP, implanted a Dolly Parton sized peak at the end to make her look scarily hotter……….and she turns out to be a Transvestite????!!!!…’
After a warm start to spring, reaching as high as 90 degrees F, I woke up today to 2 inches of snow on my deck here in New Hampshire, with a promise of more snow this evening when temps go back below freezing. My first thought was, OMG, global cooling already from the volcano?
Temps according to local weathermen are 20 degrees below normal. What do the alarmists claim it is here?
Mike Odin —
Well observed, sir.
Using that logic, regions that are still experiencing uplift from the removal of the Pleistocence icecaps should have been a focus for volcanic eruptions as well……..This isn’t science at all but plain geological baloney. But if SA supports AGW, then the editorial brains seem to have been transformed into a special type of baloney.
Meanwhile, the current Arctic Sea Ice Extent seems intent on staying ahead of the curve:
http://www.ijis.iarc.uaf.edu/en/home/seaice_extent.htm
I’m sorry Steven, but I felt compelled to post this…
“The top layer of the ice is really a ‘quasi-fluid’
This is the true reason why ice is slippery. It has to do with the properties of water when it forms ice, and it is a relatively recent discovery. When they turn to a solid, water molecules link up in hexagonal patterns (because they are polarized and can form hydrogen bonds), and these hexagons form large sheets … layer upon layer of sheets. The molecules inside a sheet are attracted to each other more strongly than to molecules in the sheets above and below. This means that the sheets can easily slide back and forth relative to the sheets above and below. A small sideways force from a skate will cause these layered sheets to slide, acting just like rollers on a conveyor belt.
Another property of ice is that the molecules on the surface are more attracted to things passing over it than they are to the other molecules of ice on the surface. The unfilled bonds of the surface molecules can grab at anything that comes near … like your foot … and be pulled out of the surface of the ice. Once they become detached they can ‘roll around’ on the surface of the ice like tiny ball bearings, making the surface slippery. ”
http://www.worsleyschool.net/science/files/myth/myth.html
🙂
Nice, Steve. Far as I have been able to figure out, increased volcanic activity rates are coincidental with low solar activity. It never occured to me that ice melting would make for extra ash. A very long period of low solar activity making for increased vulcansim in cooler/wetter times would be it’s own mechanism to further drive down temps.
It would also give rise to a possible explanation for C02 lagging.
Mean while the Greens belive the shut down in European air traffic has saved the world tonnes of C02,…but….
Stranded folks don’t tend to stay that way, there’s rail, and buses and cars and all manner of carbonising gadgetry that can move Body A to Location B.
They’re just slower, and lower than a dreamliner, hell they could even take a ferry, or a gypsy’s caravan. Segways are in…
The danger this erruption poses, it seems, is to common sense. Kudos to you sir, Steven Goddard, another cogent, well articulated article.
I abandoned New Scientist and Scientific American a year ago, I can learn more here, thanks to Antony Watts, than in any glossy covered, photo-shopped, periodical.
National Geographic,…you’re on notice too…
Pseudo-Scientific American.
Looking at the picture of the venting volcano above it seems clear that volcanic activity is a driver of climate change that we must take very seriously. While we don’t know when, it is just a matter of time before a very large volcanic eruption, or possibly a cluster of big ones, causes an episode of rapid cooling like the year without summer:
http://en.wikipedia.org/wiki/Year_Without_a_Summer
We are very unprepared for this type scenario. Shouldn’t we be diverting some of our limited resources, including some of our good climate scientists, over to researching and preparing for an inevitable rapid catastrophic volcanic cooling episode? Solar panels aren’t going to be much help when millions of people are starving to death due to crop failures…
rbateman – And won’t all this extra ash, especially if this continues, eventually fall out on glaciers and ice caps, absorb heat, and speed up their melting?
That would make the AGW gang happy.
Thank you!
Talk about smacking someone right back into their place. When I read that less ice would increase magma I knew they had completely lost their minds. Now Scientific American is no better than some third rate rag. mag.
I can see a reason for diverting aircraft around Iceland because of the potential for engine damage, but shutting down all air traffic over northern Europe seems an over reaction.
I suspect this is the air transportation version of the precautionary principle.
The analysis in this post has to do with pressures, melting points, and up and down motion. In addition to the numbers provided one might also consider the location at a divergent boundary and look at the spreading numbers. I think this region is going to have eruptions, with or without ice, until the Mid-Atlantic Ridge cools off, locks up tight, and sinks into the abyss.
http://pubs.usgs.gov/gip/dynamic/understanding.html
Divergent boundaries occur along spreading centers where plates are moving apart and new crust is created by magma pushing up from the mantle. Picture two giant conveyor belts, facing each other but slowly moving in opposite directions as they transport newly formed oceanic crust away from the ridge crest. [With map of Iceland in context.]
National Scientific American Enquirer
The S.A. article is total nonsense. The Icelandic volcanoes are in rift zones along an extension of the mid-Atlantic ridge. The crust is separating to the east and west at about the speed at which fingernails grow. Glacial ice doesn’t change that speed whether it melts or not. When the crack widens enough, basalt flows out. It’s that simple.
Typo in the article:
“The geothermal gradient of the earth is typically about 40°C per km”
should read :
“The geothermal gradient of the earth is typically about 25°C per km, or 1°C per 40 metres”
The calculations which follow were done with the correct numbers.