A series of events called earthquake swarms have impacted Yellowstone in recent weeks. The park and volcanic activity are forever linked as a hotspot sits directly underneath a massive caldera. It's a scar of the previous eruption of the "Yellowstone Supervolcano" as it has become known in popular culture. As the molten rock ebbs and flows deep underground, it causes the park to bulge outward or sink inward by a few centimeters. Mountains can lose elevation and then gain it all back in a few years.
A side effect of this molten movement are the earthquake swarms. A swarm is a series of small earthquakes all in the same general area over a span of anywhere from hours to weeks. During the peak of the swarms, 130 earthquakes were detected in the park, with the highest magnitude being 3.6 on the Richter Scale.
Earthquakes and earthquake swarms are not uncommon in Yellowstone, but there was an unusual aspect to this event. Three swarms occurred in three different areas of the park, and their activity overlapped each other. It's something that is not unprecedented, but not common either.
However, geologists maintain that if Yellowstone was getting ready for a cataclysmic eruption, we would have stronger signs than this. Swarms would be expected to be around the entire rim of the caldera, and the bulge when molten rock moves towards the surface would be much more than a few centimeters.
For the time being, these rapid series of swarms remain a curiosity; another part of the complex ecosystem of Yellowstone.