During the last couple of years I have argued that Yellowstone most likely is at the end of its life-cycle. There are many good reasons for me to believe that, let me first go through those before we move on to this week’s big news in Volcanology.
Yellowstone is currently moving into a Craton, a very old piece of crust that was among the first patches of solidified ground produced as earth cooled down. It is a very hard piece of rock to crack. The current position of Yellowstone is within an ancient crack on the rim to the Craton. The Yellowstone is cause by a hotspot/mantleplume injecting magma up that crack, this particular hotspot is not powerful enough to blast a hole through that craton. Very few mantleplumes have the capacity to blast holes through cratons.
As the North American Continent moves over the hotspot a conveyor belt of calderas have formed. From this we know that a certain caldera system is active for a period of time, normally between 2 and 3 million years, after that the spot has moved to far from the hotspot, and the hotspot comes up through another weak spot in the crust.
Previously this conveyor belt has moved through younger and weaker crust that is pretty much containing “young” thin oceanic crust that has been pressed together up against the craton. This oceanic crust made it easy for the hotspot to find weaknesses to take advantage of, now that it is moving into a craton finding new weaknesses will get progressively harder.
We also know that the hotspot punctured a hole in that faultline more than 2 million years ago, and we know that during that time the caldera has moved roughly 70 kilometers or more. This puts the current location outside of the faultline.
Lack of normal eruptions
Yellowstone is the least active of the supervolcanoes considered to be active on the planet. The last phreatic explosion occurred 13 000 years ago, and the last magmatic small scale eruption occurred 70 000 years ago.
Let us now compare this to another equally old volcano, the Tondano. Yes, it is a subduction supervolcano, not a hotspot driven one like Yellowstone. Size, age, volume… Well, they are matching up in most ways.
Tondano is erupting now, it is one of the most active volcanic centers of the planet. And it did its VEI-8 2.5 million years ago. About 1.2 million years ago it did a fairly impressive VEI-7 and it has suffered dozens of large VEI-6 caldera formations. It is a complex caldera that is a Somma formation, and to just give a bit of scale. It contains a side Somma formation the size of Vesuvius just as a side attraction. Tondano has had between 25 000 to 250 000 eruptions since its VEI-8. Currently two different volcanoes are erupting on its flanks. In comparison Yellowstone is comatose. But, this is probably how you would have found Yellowstone back in its heyday.
The 1959 Earthquake
In 1959 an Earthquake ranging between M7.3 and M7.5 occurred at Hebgen Lake adjacent to the magmatic reservoir of Yellowstone. The earthquake caused a massive landslide that killed 24 people and created the aptly named Quake Lake.
Not even this massive earthquake could cause a reaction from the shallow magmatic system of Yellowstone. This pretty much tells us that the magma down there is depleted of gasses and lack the capacity for gas nucleation to happen. To put it in an analogue. It was like if you had been shaking a bottle of champagne that have been left open for a week. It just does not have the gas to gush out any “fizz”.
Wrong type of Earthquake Swarms
During the last few years there have been earthquake swarms in the system, and this has been wildly interpreted as “Oh my GOD!!! She is gonna BLOW!!!” by the world press and those who’s imagination is running rampant on over-time.
Only problem that none of the swarms have been of a type associated with fresh magma. Some swarms have been of a type associated with magma cooling (shrinkage), another bunch have been hydrothermal, and then there have been tectonic swarms.
The hydrothermal ones have been grouped together with inflation of the caldera floor, ie, magma is moving, but it is regurgitated gas-deprived old magma. It is just the constant sloshing of magma in any large scale system.
As in any large old Caldera the magma moves from one spot to another as it shrinks, or heats up when new hot magma arrives. The first type causes small scale uplift, the other one large scale uplift. The “Oh my GODers” interpret the 2 – 5 cm per year uplift that occurred at Yellowstone as that “End of Civilization is near”. In reality this is very very small scale uplift for a volcanic caldera of this size.
Let us look at real magmatic uplift. The Campi Flegrei uplifted more than 2 meters in just a few years. This was most likely just regular magma motion. Before the last eruption Campi Flegrei outside of Naples in Italy did 7 meters in 48 hours. That is large scale magmatic intrusion. That is what would be seen at Yellowstone before an eruption, possibly even more uplift since it is a larger caldera system. Now put 5 cm annually into perspective…
Now you are saying that this has been going on and off for years. Well, it has done that. And there has been an equal amount of deflation in other areas, and the particular spot that uplifted recently has risen and fallen several times. Not that spectacular really.
Let us instead compare to the constant inflating resurgent dome of Iwo-Jima. It has an average of 12cm continuous uplift, and it never deflates. That is how a large slow eruption is built up, and it will still most likely do a sprint before erupting showing meters of rapid uplift before blowing.
Depleted Magma (The News)
This week’s big news was a research report from Ilya N. Bindeman at University of Oregon who has done work on the two last calderas that was active, the Heise and Picabo. In the geochemical work (mainly isotope) it was discovered that there is cyclicity of how the magma changed from new hot juvenile magma arrival when the calderas could supererupt, and a later stage when the magma reservoir was filled with depleted magma that basically consist of remelted crustal matter. The regurgitated crustal melt is not able to erupt, and will over time cool down.
This cycle time of possible activity is roughly two million years long, and then there is a lapse of about one million years before the Mantleplume has found virgin crust.
The mantleplume is producing hot basalt that normally would erupt in large lava floods, but as it moves up it melts the crust producing more explosive mixtures giving the Yellowstone hotspot it’s uniquely explosive eruptions. As the crust is depleted it loses its explosive capacity. And if the cycle time holds true it would now be in the end stage.
I recommend reading the links appended below, or going straight to the mentioned research papers.
If we take all of the above into account, we get a picture far from the sensationalist media. We see that Yellowstone is a geological wonder and a place of immense beauty. A phenomenon that is a living breathing large caldera slowly winding down, a sign of what is to come as we move along into the Deep Future.
Sleep well Sweet and Beautiful Yellowstone.