An ongoing earthquake swarm at Yellowstone volcano is now one of the biggest ever recorded, with over 2,300 tremors since it began in June.

As of August 30, 2,357 earthquakes had been recorded. The most powerful in recent weeks was magnitude 3.3; it took place on August 21.

The most powerful in the current swarm was a magnitude 4.4, which was recorded on June 15. Most of the earthquakes were in the magnitude 0 or 1 range, with a further 181 recorded at magnitude 2 and 11 at magnitude 3. Another 53 were less than 0, meaning they were very small events that could be detected only with sensitive earthquake-monitoring instruments.

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Jamie Farrell, a research professor at the University of Utah, which is involved in monitoring seismic activity at Yellowstone, told Newsweek that the swarm was “nothing out of the ordinary” and that it had “slowed down significantly but does occasionally have little bursts of activity that lasts for a few hours.”

yellowstone earthquake swqarm

University of Utah

Still, the ongoing swarm is now one of the longest and largest on record. The largest swarm ever recorded was in October 1985; it lasted for three months and included more than 3,000 earthquakes. There was another large swarm in 2010, when more than 2,000 events were recorded over a month.

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Thousands of earthquakes take place at Yellowstone every year. Swarms are when numerous earthquakes take place over the course of weeks or months, with no clear sequence of main earthquakes and aftershocks. They do not, as normal earthquakes sometimes do, signal an eruption is forthcoming.

The U.S. Geological Survey currently lists the volcano alert level at Yellowstone as normal, and the aviation color code—indicating a potential risk to flights—is green.

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Mark Ralston/AFP/Getty Images

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Discussing the ongoing swarm at Yellowstone at the end of June, Jacob Lowenstern, one of the scientists in charge of the Yellowstone Volcano Observatory, told Newsweek, “Yellowstone has had dozens of these sorts of earthquake swarms in the last 150 years it’s been visited. The last volcanic eruption within the caldera [crater] was 70,000 years ago. For magma to reach the surface, a new vent needs to be created, which requires a lot of intense geological activity.”

Lowenstern added, “The volcano alert level remains at green. As outlined in our response plan, USGS Circular 1351, we would need to see considerably more and larger earthquakes, combined with contemporaneous ground deformation, steam explosions and changes in gas and heat discharge, prior to moving the alert level. None of that has occurred.”

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