Carl – May 9, 2014 (re-post)
In the west corner of the ring you find Yellowstone wearing blue, red and white striped trunks and in the east corner you find Grimsvötn wearing Fire & Ice colored trunks. Welcome to a spectacular fight about who is the largest, meanest volcano on the block. As the fighters are squaring off we eagerly await for the first blow from this formidable match, and there it came, it is a stunning early knock and we have a countdown to ten. The new world champion is surprisingly Grimsvötn…
I read everything that Erik Klemetti writes and have been a big fan of his since he started the concept of volcano blogging. This week he wrote a splendid article on Yellowstone (link below) based on a paper by Jamie Farrel et al (link below) who used the earthquake data from 1984 up until 2011 to make the best mapping of the innards of Yellowstone so far. The technical part of it is described by Erik so I do not have to plow that ground here (read his piece instead).
What is interesting is that Yellowstone’s magma reservoir is now deemed to be larger than previously believed. It is now rated at between 200 to 600 cubic kilometers. Problem is just that most of it is not in the form of melt, between 85 to 95 percent is solid. Only 5 to 15 percent is now believed to be molten. This means that Yellowstone can’t erupt in its current state.
And if we assume a maximum intrusion rate of 1 cubic kilometer per year it would still take between 68 years and 228 years at best until Yellowstone reached the presumed barrier for when an eruption can occur. On top of that there is no evidence at all that magma is intruding into the magma reservoir at that speed. If it had done that Yellowstone would erupt quite often (every few years or so). In reality the magma influx seems to be miniscule at Yellowstone, if it is even influxing at all.
This is really bad news for Yellowstone, but I guess that the Bison’s will be happy to know that they will not be blown off the face of the planet.
Now, let us look at a volcano that has a comparative magma reservoir and a proven influx of magma rated at the astonishing speed of 0.1 cubic kilometer per year and compare how that volcano behaves. Remember, this volcano is de facto more active and is today a far larger and more dangerous volcanic system than Yellowstone, so let us travel to the land of Ice and Fire.
First of all let us start with what Grimsvötn is not, and that is a Supervolcano. It has never suffered a VEI-8 eruption, nor will it ever. But it is a supererupting volcano none the less. In 8230BC the volcano suffered the VEI-6 Saksunarvatn tephra, in an explosive caldera forming eruption. It was the third known caldera forming eruption of Grimsvötn.
In that eruption large parts of the magmatic reservoir was destroyed, but the deep feeder system was still intact. And during the last 10 000 years the reservoir has built up to a prodigious size. The volume above the Curie-point is 400 cubic kilometers.
Now, the Curie-point is where a material becomes too hot to be magnetic. That does not in and of itself state that it is a melt. But it says something about the temperature the magnetic elements are in. Let us dwell a bit on temperatures.
For instance we know that artificial Yttrium Iron Garnet has the lowest known Curie-point at 287 degrees Celsius, but that one does not exist in Grimsvötn or any other volcano. The lowest temperature compound that could be found in Grimsvötn is Fe2O3 (hematite) with a Curie-point of 675 degrees Celsius. At that temperature some of the magma would be solid but melt would most likely be higher than at Yellowstone.
We do though know that the heat influx is great and that the volcano has ready access to nicely melted material in abundance. In fact, we know that the volcano is well above the required 40 percent melt for buoyancy driven eruptions. In most likelihood the Curie-point is the same as, or even above, that of pure iron (770C).
Now, how come that a non-supervolcano can have more eruptible magma than a VEI-8 brute like Yellowstone? Well, that answer is trickier to give. Basically it all boils down to the amount of energy entering the system, and that energy arrives in the form of heat carried by arriving magma from the mantleplumes residing under Yellowstone and Grimsvötn.
In Grimsvötns case that is 0.1 cubic kilometer of basalt at a temperature of 1 150 degrees Celsius per year and that is quite a lot of energy. If we compare that to Yellowstone it seems like almost no new heat is arriving, or a very tiny amount of it.
The evidence of this is that there is very little evidence of Yellowstone suffering from a resurging dome (inflation of the center of the caldera). In all likelihood Yellowstone has not received any new magma in the last 70 000 years. Remember that it takes quite a while to cool down a very large magma reservoir until it is almost all solid.
If we compare that to Grimsvötn who has received in the neighborhood of 800 cubic kilometers of fresh hot magma in the last 10 000 years you can understand the difference in energy input into that volcanic system. Those of you who are into math will now be collecting your jaws from the floor. Yes, Grimsvötn has erupted in the order of 400 cubic kilometers in 10 000 years, or on average 0.04 cubic kilometers per year (as Tephra and lava).
But, the figures grow even more stumping if we look at the amount erupted in the last 250 years. Without counting the Skaftár Fires (Lakí eruption) Grimsvötn has had 28 confirmed eruptions ranging from VEI-2s to the large VEI-4 2011 eruption. Together with the 3 cubic kilometer Dense Rock Equivalent and 15 cubic kilometer flood basalt of Lakí we get a volcano that has erupted as much or even more lava than the received magma influx.
The 2011 eruption caught most scientists with their pants down since they did not believe that the eruption would be so big, but in hindsight it is easy to see that a magmatic system of that caliber can erupt a large volume without a long repose time.
This tells us that the magma reservoir is now at its limit of what it can hold, everything that goes in comes out as quickly, and as time goes by the risk of another caldera forming event increases, and most likely Grimsvötn is already teetering on the brink for one. The other risk is obviously a repeat of the Lakí-event, and that is not such a small risk. After all Iceland regularly suffer those at a rough 270 year interval (sometimes Iceland skips a cycle, remember that, nothing is ever certain around volcanoes).
Of course a caldera forming explosive eruption or a large scale flood basalt would impact global weather, especially in the northern hemisphere. But for those who Dream Dark Dreams of Destruction, it will be a large nuisance and not a catastrophe.
I am terribly sorry that I once again spanked the Doomsayers favorite volcano. Those people should understand that there is no cover-up, nor am I and every other scientist on the planet trying to fool them. It is nature herself that is against their Dark Dreams; Yellowstone is for all points and purposes no longer a volcano. End of discussion.