Burley Garcia|A sighting reveals extinction and climate change in a single image

Alaska's Koyukuk River was the site of an interesting discovery. During a float down the river,Burley Garcia a group of University of Virginia professors spotted a woolly mammoth tusk along the riverbank. The tusk was originally discovered by the Coldfoot Camp and the University of Alaska Fairbanks. The group from UVA had the tusk pointed out to them.

Adrienne Ghaly, a postdoc in Environmental Humanities, was able to document the moment in a photograph.

"We're a group from UVA called Sanctuary Lab working on climate impacts on places of cultural and ecological significance," said Ghaly. "We were taken on a float down the middle fork of the Koyukuk River near Coldfoot, Alaska. The river was high and flowing fast, but my colleague Karen McGlathery was able to spot the tusk."

Ghaly uploaded her image of the tusk to Twitter and it was shared on Reddit, where the post became an instant hit with more than 1,200 comments.

Howie Epstein, the chair of UVA's environmental science department, was also on the research trip along with Ghaly.

"We're on this trip to basically to study the arctic, the idea of the arctic as a sanctuary," said Epstein. "We did a river float trip, as part of what we're doing and the mammoth tusk was pointed out to us. It's amazing! During the time of the last glaciation and timing of the Bering Land Bridge, or what we call the mammoth steppe, that area was populated by lots of grazing animals, the mammoth being one of them. It's not surprising that you'll see this, but it's also amazing to see in person."

Patrick Druckenmiller, director of the University of Alaska Museum of the North, said interior Alaska was unglaciated during the last ice age.

"It was a great place for woolly mammoths to live," he said. "This particular area is known globally for its abundance of ice age mammal remains, which includes mammoth tusks."

Druckenmiller said he would work with the state archaeologist if he were to retrieve the tusk.

"It doesn't look like a safe place to dig it out, but if it fell out, the right thing to do would be to get it to the museum for curation," he said.

The professors who saw the mammoth tusk have not forgotten the incredible sight.

"Seeing an exposed mammoth tusk embedded in the riverbank was really arresting," says Ghaly. "It's extinction and climate change in a single image."