犹他州南部发现史前超级火山

Brigham Young University geologists¹ found evidence of some of the largest volcanic² eruptions⁴ in earth's history right in their own backyard. These supervolcanoes aren't active today, but 30 million years ago more than 5,500 cubic kilometers of magma erupted during a one-week period near a place called Wah Wah Springs. By comparison, this eruption³ was about 5,000 times larger than the 1980 Mount St. Helens eruption.   "In southern Utah, deposits from this single eruption are 13,000 feet thick," said Eric Christiansen, the lead author for the BYU study. "Imagine the devastation⁵ - it would have been catastrophic to anything living within hundreds of miles."   Dinosaurs⁶ were already extinct during this time period, but what many people don't know is that 25-30 million years ago, North America was home to rhinos⁷, camels, tortoises and even palm trees. Evidence of the ancient flora⁸ and fauna⁹（动植物） was preserved by volcanic deposits.   The research group, headed by Christiansen and professor emeritus¹⁰ Myron Best, measured the thickness of the pyroclastic flow deposits. They used radiometric dating, X-ray fluorescence spectrometry, and chemical analysis of the minerals to verify that the volcanic ash was all from the same ancient super-eruption.   They found that the Wah Wah Springs eruption buried a vast region extending from central Utah to central Nevada and from Fillmore on the north to Cedar¹¹ City on the south. They even found traces of ash as far away as Nebraska.   But this wasn't an isolated¹² event; the BYU geologists found evidence of fifteen super-eruptions and twenty large calderas. The scientific journal Geosphere recently published two of their papers detailing the discoveries.   Despite their enormous size, the supervolcanoes have been hidden in plain sight for millions of years.   "The ravages¹³ of erosion and later deformation¹⁴ have largely erased¹⁵ them from the landscape, but our careful work has revealed their details," said Christiansen. "The sheer magnitude of this required years of work and involvement of dozens of students in putting this story together."