<P> Volcanic and tectonic actions in the region cause between 1,000 and 2,000 measurable earthquakes annually . Most are relatively minor, measuring a magnitude of 3 or weaker . Occasionally, numerous earthquakes are detected in a relatively short period of time, an event known as an earthquake swarm . In 1985, more than 3,000 earthquakes were measured over a period of several months . More than 70 smaller swarms were detected between 1983 and 2008 . The USGS states these swarms are likely caused by slips on pre-existing faults rather than by movements of magma or hydrothermal fluids . </P> <P> In December 2008, continuing into January 2009, more than 500 quakes were detected under the northwest end of Yellowstone Lake over a seven - day span, with the largest registering a magnitude of 3.9 . The most recent swarm started in January 2010, after the Haiti earthquake and before the Chile earthquake . With 1,620 small earthquakes between January 17, 2010, and February 1, 2010, this swarm was the second largest ever recorded in the Yellowstone Caldera . The largest of these shocks was a magnitude 3.8 which occurred on January 21, 2010 . This swarm reached the background levels by February 21 . On March 30, 2014, at 6: 34 AM MST, a magnitude 4.8 earthquake struck Yellowstone, the largest recorded there since February 1980 . </P> <P> The last full - scale eruption of the Yellowstone Supervolcano, the Lava Creek eruption which happened approximately 640,000 years ago, ejected approximately 240 cubic miles (1,000 km) of rock, dust and volcanic ash into the sky . </P> <P> Geologists are closely monitoring the rise and fall of the Yellowstone Plateau, which has been rising as fast as 0.6 inches (1.5 cm) per year, as an indication of changes in magma chamber pressure . </P>

What is the diameter of the yellowstone caldera