Yellowstone's world-famous natural history is marked by such colossal volcanic events that their reflections in today's landscape are difficult to grasp and impossible to take in at just a glance, even for those familiar with the signs of past volcanism. Three extraordinarily large explosive eruptions in the past 2.1 million years each created a giant caldera within or west of Yellowstone National Park with the spread of enormous volumes of hot, fragmented volcanic rocks as pyroclastic flows over vast areas within times as short as a few days or weeks. The accumulated hot ash, pumice, and other rock fragments welded together from their heat and the weight of overlying material to form extensive sheets of hard lava-like rock. In some sections, these welded ash-flow tuffs are more than 400 m thick! These ash-flow sheets—from oldest to youngest, the Huckleberry Ridge, Mesa Falls, and Lava Creek Tuffs—account for more than half the material erupted from Yellowstone. The enormous outpouring of magma, 280 to 2,450 km3 during each explosive event, led to the collapse of magma-chamber roofs, causing the ground above to subside by many hundreds of meters to form the calderas.

Accelerated Uplift and Magmatic Intrusion of the Yellowstone Caldera, 2004 to 2006by Wu-Lung Chang, Bob Smith, Chuck Wicks, Jamie Farrell, and Christine Puskas Published in Science on November 09 2007 The Yellowstone caldera began an extraordinary episode of ground rising in mid-2004, revealed by GPS (Global Positioning System) and InSAR (Interferometric Synthetic Aperture Radar) measurements, at rates up to 7 cm/yr that is over three times faster than previously observed inflation rates. The caldera-wide accelerated upli ft is interpreted as magmatic recharge of the Yellowstone magma body. While the geodetic observations and mo dels do not imply an impending volcanic eruption or hydrothermal explosion, they are important evidence of on going processes of a large caldera that was produced by a super volcano eruption.