An earthquake swarm “on the large side” struck the Yellowstone National Park on Thursday, according to the US Geological Survey (USGS). The swarm hit the US supervolcano southwest of Yellowstone Lake, Wyoming, between Heart Lake and West Thumb. Yellowstone volcano is among the most seismically active parts of the US but amid the coronavirus pandemic, raging California wildfires, and widespread civil unrest, any sign of possible unrest at Yellowstone is unwelcome news.
One Twitter user said: “Although I don’t particularly doubt the science and the chance of triggering an eruption is basically inconceivable, 2020 is just not the year to be messing about with things like Yellowstone’s magma chamber.”
Another person said: “At this rate, it’s probably safe to assume the Yellowstone supervolcano AKA ‘the Big One’ will erupt in the next month or two.”
And a third person said: “I almost have a blackout BINGO on my 2020 card, but the only thing left is ‘Yellowstone Supervolcano’.”
Yellowstone’s last three big eruptions went off roughly 2.1 million, 1.3 million and 640,000 years ago – an interval between 0.8 and 0.66 million years between eruptions.
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This cycle has led some to falsely believe Yellowstone erupts like clockwork and is overdue another blast.
This, of course, is not true as the USGS has said: “One cannot present recurrence intervals based on only two values. It would be statistically meaningless”
So what exactly is going on in the Yellowstone caldera that prompted the earthquake swarm?
According to Michael Poland, chief scientist at the Yellowstone Volcano Observatory (YVO) branch of the USGS, earthquake swarms are par for the course in Yellowstone.
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The US park experiences between 1,500 and 2,000 earthquakes every single year and roughly 50 percent of all seismicity is accounted for by swarms.
He said: “Yellowstone has had swarms that include many hundreds of earthquakes in a day.
“For example, there was a three-month-long swarm that occurred in June-September 2017 with 2,400 located earthquakes and maximum (magnitude) 4.4.:
The most recent swarm failed to even peak at magnitude 3.
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The strongest tremor in swarm was recorded at magnitude 2.8 and the weakest was just 0.1.
Interestingly, some of the 91 tremors were artificial, triggered by a seismic vibrator truck passing through the national park.
Seismic vibrators or vibroseis trucks are trucks or buggies designed to produce vibrations in the ground’s surface.
The truck passed through Yellowstone’s Old Faithful, West Thumb, Canyon Village and Lake Butte as part of a University of Utah and University of New Mexico experiment.
So the earthquake swarm was not out of the ordinary, even if it was “the best-recorded earthquake swarm in Yellowstone ever”.
Dr Poland said: “So, the 91 quakes were real quakes and it happened to occur when there is also a synthetic experiment happening, which is really cool because it means the natural swarm was ‘seen’ by hundreds of temporary seismometers.”
The USGS also tweeted after the swarm: “Happily, the volcano doesn’t know what year it is.
“And even more happily, the Yellowstone magma chamber is mostly solid!”