The Yellowstone caldera lays beneath the states of Wyoming, Montana and Idaho and is constantly monitored by the USGS for signs that a supereruption is on its way. While most seismic activity at the park is nowhere near the levels needed to trigger an eruption, the 1959 Hebgen Lake earthquake that occurred on August 17, 1959, was a different story. The 7.5 magnitude quake caused massive damage, including 28 fatalities and a considerable £9million (£200million today) in repairs to highways and timbers.