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the magma in the volcano, causing a sudden and violent expansion of gases that blasted through the side of the volcano. Rock, stream, and ash screamed north at the speed of sound and flattened a forest and everything in it over an area of 600 square km. Johnson, along with 60 others, vanished forever. When the eruption was finally over, the once cone-like peak of Mt. St. Helen had disappeared—the summit now lay 440 m lower, and the once snow-covered mountain was a gray mount with a large gouge in one side. Mt. Pinatubo, 1991 C.E., 10km3(2.4 cubic miles)Krakatau, 1883 C.E., 18km3(4.3 cubic miles)Krakatau, a volcano in the sea between Indonesia and Sumatra, where the Indian Ocean floor subducts beneath Southeast Asia, had grown to become a 9-km-long island rising 800 m (2,600 ft) above the sea. On May 20, the island began to erupt with a series of large explosions, yielding ash that settled as far as 500 km away. Smaller explosions continued through June and July, and steam and ash rose from the island, forming a huge black cloud that rained ash into the surrounding straits. Ships sailing by couldn’t see where they were going, and their crews had to shovel ash off the decksKrakatau’s demise came at 10 am, on August 27, perhaps when the volcano cracked and the magma chamber suddenly flooded with seawater. The resulting blast, five thousand times greater than the Hiroshima atomic bomb explosion, could be heard as far as 4,800 km away, and subaudible sound waves traveled around the globe seven timesGiant waves pushed out by the explosion slammed into coastal towns, killing over 36, 000 people. Near the volcano, a layer of ash up to 40 m thick accumulated. When the air finally cleared, Krakatau was gone, replaced by a submarine caldera some 300m deep. Vesuvius, 79 C.E., 25km3(6 cubic miles)Crater Lake, 7600 B.C.E., 75 km3(18 cubic miles)Tambora, 1815 C.E., 145km3(35 cubic miles)
Phlegrean Fields, 40, 000 B.C.E., 200km3(48 cubic miles)Yellowstone1.3 Ma, 250km3(62 cubic miles)Yellowstone National park lies at the northeast end of a string of calderas, the oldest of which, at the southwest end of the track erupted 16 million years ago. Recent and ongoing activity beneath Yellowstone has yielded fascinating landforms, volcanic rock deposits and geysers. Eruptions at the Yellowstone hotspot differ from those in Hawaii in an important way: unlike Hawaii, the Yellowstone hot spot erupts both basaltic lava and rhyolitic pyroclastic debris.Yellowstone, 630, 000 B.C.E., 1, 000km3(240 cubic miles)About 630, 000 years ago, immense pyroclastic flows, as well as convective clouds of ash and pumice lapilli, blasted out of the Yellowstone region. Close to the eruption, ignimbrites up to tens of meters thick formed, and ash and lapilli from the giant cloud sifted down over the US as far east as the Mississippi RiverThe eruption produced an immense caldera, up to 72 km across. When the debris settled, it blanketed an area of 2, 500 square km with tuffs that, in the park, reached a thickness of 400 m. The park’s name reflects the brilliant colour of the volcaniclatic debris