Introduction
Summit calderas form on preexisting composite volcanoes at the end of large-volume, climactic eruptions that empty the magma chamber beneath the summit. Caldera-collapse occurs along ring fractures as the summit area founders into the space previously occupied by the shallow magma reservoir.
Summit calderas make some of the most striking volcanic landscapes in the National Park System.
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Aniakchak Caldera in Alaska, with its series of lava domes, maars, and other vents along with its warm springs and young lava flows within its caldera walls, contains abundant evidence of post-caldera volcanism. The most recent eruption at Aniakchak took place in 1931.
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The beauty of today’s Crater Lake National Park belies the violence of the lakes origin at the end of the eruption that destroyed Mount Mazama. The preexisting Mazama composite volcano had an elevation of approximately 12,000 ft (3,700 m). The eruption blanketed an area of more than 650,000 square miles (approximately 1.7 square km) across the western United States and southwestern Canada with volcanic ash.
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The caldera at the summit of Mount Katmai formed during the Valley of Ten Thousand Smokes eruption in 1912. This eruption lasted about 60 hours and transformed a verdant valley rich with wildlife into a desolate expanse covered by pyroclastic flow deposits smoking with superheated fumaroles. The primary vent for this eruption was Novarupta, a separate vent approximately 6 miles (10 km) from Mount Katmai.
Source: U.S. Department of the Interior, National Park Service
