Alaska’s Calderas Rival Yellowstone and Most Americans Have Never Heard of Them

When Americans think of volcanic calderas, Yellowstone National Park tends to dominate the conversation. It makes sense as Yellowstone is home to over 10,000 hydrothermal features, but the most active caldera systems in the United States aren’t in Wyoming. They’re in Alaska and some of them erupted far more recently than Yellowstone’s legendary supervolcano events.

According to the USGS Yellowstone Volcano Observatory, Alaska hosts 12 calderas that formed within the last 12,000 years, all strung along the Alaska-Aleutian subduction zone where the Pacific plate dives beneath the North American plate. While they’re all pretty interesting, three stand out as particularly significant.

Aniakchak, on the Alaska Peninsula, experienced a major caldera-forming eruption roughly 3,500 years ago. That event produced around 100 cubic kilometers of magma and generated tsunamis, wiped out populations across the central Alaska Peninsula, and disrupted global climate. Fisher Caldera on Unimak Island is one of the largest in the entire arc, measuring 11 miles long and 7 miles wide. It formed about 9,400 years ago during an eruption powerful enough to send pyroclastic flows all the way to the Pacific Ocean.

Perhaps the most interesting, Okmok Caldera on Umnak Island erupted roughly 2,050 years ago. Researchers believe that event triggered climate disruptions reaching as far as Ancient Rome, contributing to crop failures and famine during an already unstable political period.

All three eruptions were 10 to 20 times smaller than Yellowstone’s most recent caldera-forming event, but each still dwarfs the 1980 Mount St. Helens eruption by more than 200 times.

The key difference between these systems and Yellowstone comes down to tectonic setting. Yellowstone sits above a hotspot while Alaska’s calderas are products of subduction, which changes everything from magma composition to eruption frequency. Whatever the case, the geology of the Aleutians deserves far more attention.

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