The story

Japanese police and U.S. Air Force helicopters were searching Friday for an American university professor who disappeared on a tiny volcanic island in Japan.

Craig Arnold, a 41-year-old assistant professor at the University of Wyoming, did not return from his Monday hike to a volcano on Kuchinoerabujima, a small island in southern Japan, the school said.

"The only clues that [searchers] have found were indications that he had begun the ascent -- footprints on the trail," said Peter Parolin, head of the university's English department, citing Arnold's family. Read full article »

CNN's Jason Hanna and Yoko Wakatsuki contributed to this report.

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