So what is the latest with the ongoing earthquake swarm at the Yellowstone supervolcano caldera? Here is my just-completed email chat with Dr. Jacob Lowenstern of the U.S. Geological Survey, top scientist at the Yellowstone Volcano Observatory:
How would you characterize the recent level of seismic level? Terms like "swarm" are pretty alarming. How would place this level of activity in historical context to what the USGS/YVO have tracked before?
Lowenstern: Swarm refers to seismicity when there isn't a typical mainshock/aftershock sequence. In other words, the events are more similar in size. Swarms are very common at Yellowstone. This one is clearly bigger than normal, and is the largest since 1985. There were also some large swarms in the 1970s, but the seismic network was much cruder at that time and we weren't able to locate earthquakes as well.
Me: What might be the markers/indicators leading up to a major volcanic/seismic event? Do you think this is leading to a volcanic eruption of some sort? What does your gut tell you?
Lowenstern: The most likely "bad" things that could happen would be triggering of a larger earthquake or some sort of steam explosion set off beneath the lake. At this point, any kind of volcanic eruption is a long shot. That's why we haven't called for a volcano advisory. None of our other monitoring indicators show anything that is nearly so anomalous as the earthquakes. At this point, the most likely thing is that the swarm will continue, perhaps for weeks, and then will end without any other related activity.
Me: It is all or nothing? I mean, do we either get lots of small quakes leading to nothing vs. a supervolcano? Could there be grades of eruptions or events?
Lowenstern: There are LOTS of things in between. There have been 80 volcanic eruptions at Yellowstone since the last "supervolcano" eruption 640,000 years ago and hundreds of large steam explosions, some near the Lake. It is FAR more likely that we'd have a steam explosion or a small volcanic eruption than a supereruption. By the way, the last time a volcanic eruption occurred at Yellowstone was 70,000 years ago.
Me: So if we were leading up to a major event, what sorts of indicators might we expect to see? We haven't seen one in a long time.
Lowenstern: It is certainly an issue that the truly major events are not known on a human timescale. We've mostly witnessed the precursors to smaller eruptions. But before any kind of an eruption we'd expect a whole lot of change in the ground deformation as measured by GPS. Nothing has changed over the past week. We'd also expect larger earthquakes and a bunch of steam explosions before magma ever made it to the surface.
Me: What do you make of this comment from one of my readers: "It's not that there's lots of quakes or even that they're all within a mile or two of each other, the worrisome part is that they are all a few hundred yards apart from the surface down to 7.2 km defining a single chimney under high pressure causing radial fractures along its entire length. NPS says the magma chamber is as high as 8 km and if it is that close to the chimney reaching to 7.2 km, we may be in for an eruption. We need more info on this location and USGS should deploy the best seismic testing equipment in the Lake NOW."
Lowenstern: That is pretty fanciful. We've got a team of seismologists looking at the data. The swarm is over a 7 km length right now. None of the earthquakes are that big, so it may be that fluid pressure is moving around as rocks break and thus breaking new rocks. It's also important to realize that when your seismic stations are 10s of kms apart, you can't get good resolution on the depth. The best located earthquakes right now are shallower than 5 km, but greater than 3 kms. Most of the shallower reported depths are probably inaccurate.