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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I have a great deal of difficulty believing that the isostatic change or ice cap weight have anything to do volcanic events in a slip zone fault.
Doesn’t the presence of the ice cap increase the ash production, if anything the current problems in Europe are exacerbated by the fact that the glaciers haven’t melted fast enough. If the AGW alarmists were right, thousands wouldn’t be stranded right now.
“stevengoddard (06:56:42) :
Piers Corbyn (20:22:50) :
I’ll be keeping an eye on your volcano forecasts, but I am extremely skeptical ……”
Piers just said there could be renewed acitvity at his SWIPs around the 18th to 24th April.
I work with Piers in the Weather Action team, and specialise in temperature variation, and have discovered the connection between temperature rises, and new volcanic activity. I have forecast nearly every period of new activity since November 2008. The recent Iceland eruption fits the theory well, with the eruption occuring on this very warm start to April. Also see this post (09:35:41) for local conditions.
Iceland volcanoes can actually continue billowing stuff out for weeks, months or even years.
I am fascinated by these posts. I have learned more today about volcanoes (and why ice is slippery!) than I had ever known.
If an English teacher, venturing into this science blog, may make two requests:
1. In a comparison, use “different from,” not “different than.”
2. In an explanation, use “the reason is that…,” not “the reason is because…”
I could explain the grammar, but it’s not nearly as interesting as volcanoes.
Can someone tell me, just an estimate please, how much of these greenhouse gases are being emitted from the volcano over the last couple of weeks compared to how many vehicles it would take to emit the amount that has been emitted over the last few weeks.
This comparison is crucial in understanding human impact on global warming versus natural causes.
A little off topic but B.A. and KLM plus the Germans, have been running test flights and finding no damage/problems.
Nice to note that the aviation shutdown by the air traffic controllers was based on a Met Office model! There are now many claims of over reaction based on the model. Passenger safety versus company profit? Who can tell?
Thanks Steve that’s very useful. I was the one that posted elsewhere about the idea of pressure release. The idea is way older than Scientific American lets on. Funny how warmists never go in for accurate references in these cases. My assumption was that the melt produced increased water that reacted the magma to increase the probability of an explosive release. I see you’ve dealt with that too in the next volcanism post.
Nice to know I hadn’t missed a post.
If the premise in “Scientific American” is correct, would it not be a “good” thing? Volcanic eruptions and earthquakes will happen eventually. The longer they wait the more intense the event. If this were anything other than “post-modern science” there would be a mention of the potential benefit of letting off a comparatively little amount of steam rather than building to a cataclysmic event. Thinking of earthquakes, would it be less damaging to have a 5.0 earthquake every year for 100 years on the San Andreas, or a 7.0 once every hundred years? (I know the amount of energy released from a 7.0 is more than 100 times the amount of a 5.0, but isn’t the displacement about the same?)
After a bit more research into the interesting geologic structures (Bookshelf and near vertical faulting) that occur in Iceland and the massive rift zone systems, glacial pressure appears to be a reasonable factor. Clearly, the events are driven by magma supply but…
Geology and geodynamics of Iceland
R.G. Trønnes, Nordic volcanological Institute, University of Iceland
source: http://www2.norvol.hi.is/Apps/WebObjects/HI.woa/1/swdocument/1006551/Introduction+to+Geology+and+geodynamics+of+Iceland+-+Reidar+Tršnnes.pdf
page 13:
Glacio-isostatic modulation of volcanism
The low viscosity of the high-temperature upper mantle and lower crust makes the pressure release melting very sensitive to rapid glacial unloading and rebound. The link between deglaciation and increased volcanic productivity has been noted in many different parts of Iceland: the Reykjanes Peninsula (Jakobsson et al. 1978), the Vei•ivötn fissure swarm in the ERZ (Vilmundardóttir and Larsen, 1986), the Askja (Sigvaldason et al, 1992) and •eistareykir (Slater et al. 1998) volcanic systems of the NRZ and the Snæfellsjökull system (Hardarson and Fitton, 1991). The unloading effect leads to nearly 100 times higher volcanic productivity than that of recent times (< 5 ka BP) and during glacial periods (Maclennan et al. J. Geophys Res., submitted).
The magmas erupted during the periods of maximum productivity in the glacial rebound stages are the most primitive magmas recorded in Iceland. Almost all of the accessible picritic eruption units and most of the large monogenetic shield volcanoes of primitive olivine tholeiitic composition are of early post-glacial age. These relationships demonstrate that the crustal magma plumbing system has inadequate capacity for melt processing during periods of large magma supply from the mantle.
In the early and mid 1980’s I attended several corporate sponsored presentations by a climatologist who related vulcanism to global cooling and predicted significant cooling in coming years. His ideas were based upon geologic history with a bit of astronomical tidal forces thrown in to boot. Anyone out there know of whom I speak? He was in his eighties then and is long gone now.
By the way, as an engineer and fairly competent statistician my bet after much reading of the various evidence available is that anthropogenic global climate change of any kind is pure bull fecal material.
Jim, pure bull fecal matter causes global warming. The potential increase in geological activity on the other hand will be “climate change”. There are theories that the intensity, and lack thereof, of solar cycles has an impact on Earth’s geological activity. These theories seem at least as credible to me as AGW climate models.
Alan Cheetham (12:37:32) :
In 2000 the Guardian said the largest glacier would be gone in 5 years – it hasn’t changed much in 10 years.
For an examination of Iceland climate data, volcanoes and glaciers, including the Guardian’s old claim, see:
http://www.appinsys.com/globalwarming/RS_Iceland.htm
—…—…—
OK. So, let us assume that this “theory” – that global warming caused the Icelandic glaciers to melt, which lowered the pressure on the volcano’s core, which allowed the magma to leap out and spew millions of tons of ash tens of thousands of meters into the air – might be true.
A few pertinent questions come to mind – that NOBODY has seen fit to ask yet.
First: Did ANYBODY doing this “Scientific America research” for their article verify that :
(1) the 1/2 of one degree (maybe !!! – if surface records are correct) of actual global warming since 1970 was actually enough rise in temperature to actually MELT the glaciers worldwide as has been claimed in tens of thousands of articles and IPCC-quoted “research” papers?
(2) If that 1/2 of one degree of warming was actually enough to melt the glaciers “as consensus claims” – then the ten years of continued constant temperature should be visible in the change of glacier mass.
After all, we are continuously told that the 25 years of rising temperature caused the glaciers to melt, so a ten year period of constant temperature should be just as visible in the glacier record. (No further increase in glcier melt, no change in glacier melt rate -rather than an accelerating glacier melt rate as (assumed !!!) between 1973 and 1998, etc….)
(3) Did the one particular glacier atop this particular mountain actually recede as implied?
We KNOW that only about 1/3 of the world’s glaciers are retreating = therefore, we CANNOT assume that this glacier retreated between the 1973 and 2010, as implied by the article.
(4) If this one aparticular glacier did actually melt, how much mass was lost?
No guesses, no wave-the-hands-in-front-of-a-camera and spout Gaea principles of AGW-inspired meltdowns.
How much glacier mass actually melted, and what was the original mass of rock and stone over the magma, and what caused the previous hundreds of eruptions on this mountain at what frequency? Was THIS PARTICULAR eruption so early that something different (glacier melt) clearly cause it?
(5) Volcanoes shrink and swell by tens of meters over their lifespans – between the eruptions that (literally !) move mountians hundreds of miles and lift tons of debris thousands of meters.
What was the trend of this particular vocano’s swell (uplifting) between the hot temrpoatures of the mid-1930’s through the cold period of 1945 – 1973, and the warming period from 1973 through 2010?
What actual EVIDENCE is there that there is actually ANY change (acceleration or deceleration between any ten year period of that series of measurements – and if there are no measurements, then this whole article is a fantasy – that indicates ice melt might have influenced the swelling of the mountain.
(6) I might include also this question: If this particular glcier melted in the past few years – which has not been verified to date – where did the “melt” occur?
At the foot of the glacier, with upper regions still about the same?
Then unless the magma swell was also at the foot of the mountain, the glacier mass had no effect on the magma coming up through the mountain rock higher up. (If anything – a lower mass lower down the slope of the mountain would indicate that the eruption should be sideways – like at Mt St Helens where the side of the mountain slid down, and the ash was blown out sideways, no from the crater at the peak.
At the peak (upper end of the glacier mass? If so, where was the magma pushing up before and after the glacier melt?
If it could be claimed to be “general ice mass loss” – then what was the ACTUAL percent of mountain mass compared to glacier mass – before and after the assumed melting?
How was mountain mass calculated? How was glacier mass estimated? Who – and what agenda did the assumers have – did the estimations of glacier mass loss?
carddan,
Precession (wobble in the earth’s spin, earth’s orbital shift (the shape of the orbit acually changes over long periods of time) and actual axial inclination change all occur in a cyclical fasion which has been related to geologically historical glaciatians. The amount of solar radiation recieved by the northern hemisphere, in particular, due to these changes can vary significantly, causing heating and cooling. Never heard that these variations had effect on vulcanism, but it would make sense given the changes in tidal forces acting upon the magma which could result.
In any event, wish I could remember the name of the old climatologist from the 80’s but senility is creeping up on me. The forces of nature are so profound compared to any effects tiny creatures such as man have upon our planet that AGW is nothing more than a trbute to the vanity and dishonesty of very small men in search of the dollar.
And, yes, the bovine excrement does creat methane, a green house gas but so do private jets, 24000 sq ft houses and all the hot air expelled at conferences discussing such nonsense as AGW.
The greater compression effect is on Antarctica—as ice flows with the loss of lateral support from disintegrating ice shelves, the pressure reduction will eventually allow the pent up energy to explode. melt water will cause sea levels to rise dramatically in a few weeks at most. There is reason to hypothesize that earlier explosions in Iceland in ancient times may be the basis for the accounts in Plato. Hence “ancient” not prehistoric. Ask Noah This has nothing to do with manmade CO2. It is a periodic coinciding cycles–peaking now. Lst time was 720,000 years ago –a 2 cusp cycle–this length interglacial only every 720,000 years. The compression and subglacial expansion can be measured by space-based topo measurement. The weights and pressures can be estimated and the blowup roughly predicted.