Geography
Yellowstone's supervolcano caldera is bigger than some small countries
Beneath Yellowstone National Park lies a caldera roughly 30 by 45 miles wide, carved by a cataclysmic eruption about 640,000 years ago that followed two even larger blasts. USGS monitoring shows the magma chamber underneath is mostly solid rock, only 5-15% molten, and supereruptions have occurred on average only a few times every couple million years. Despite its fearsome nickname, geologists see no sign Yellowstone is due to blow again anytime soon.