Yellowstone commonly experiences “earthquake swarms”—a series of earthquakes over a short period of time in a localized area. The largest swarm occurred in 1985, with more than 3,000 earthquakes recorded during three months on the northwest side of the park. Hundreds of quakes were recorded during swarms in 2009 near Lake Village and 2010 between Old Faithful area and West Yellowstone. Scientists posit these swarms are due to shifting and changing pressures in the Earth’s crust that are caused by migration of hydrothermal fluids, a natural occurrence of volcanoes.