A bison in Yellowstone National Park appeared to stumble into the scalding water of Grand Prismatic Spring, causing its death as tourists looked on during the park's busiest season.
The bison fell into the hot spring at Midway Geyser Basin near Old Faithful early Saturday, a spokesperson for Yellowstone said.
It's not entirely clear exactly how or why the animal ended up in the hot spring, said Michael Poland, the scientist-in-charge at Yellowstone Volcano Observatory and a geophysicist at the U.S. Geological Survey.
But after having seen video of the accident, Poland said it looked like the bison got too close, stumbled further into the water and thrashed around before it fell into an even hotter part of Grand Prismatic, causing its death.
Poland said the bison died "fairly quickly," and he dispelled rumors that the spring's water is highly acidic, causing the animal to burn.
Most hot springs are actually neutral, Poland said, but the temperatures are so extreme that the bison most likely boiled to death.
Grand Prismatic is about 300 feet wide, and its temperatures reach 192 degrees Fahrenheit, Poland said. Boiling point at Yellowstone, because of its high altitude, is 200 degrees Fahrenheit.
"This bison carcass is basically sitting in a pool of nearly boiling water, and ... that boiling water will eat away at the organic material, the tissues, and eventually there will just be some bone" leftover, he said.
It's not the most uncommon of occurrences, Poland said. Often, animals will walk along the edges of hot springs. They can fall in because the crust surrounding the pool is thin and can break with enough weight.
"It's possible something like that happened," he said. "Perhaps a little shelf that [the bison] was standing on collapsed and that exposed [it] to more hot water."
Poland added: "But I can't say for sure."
He noted that he has never heard of that happening at Grand Prismatic before. Scientists know it occurs at least from time to time, though, because animal skeletons can be found at hot springs around the park, many of which are in the backcountry, away from tourist activity, Poland said.
What makes this case unique is that the bison died in Yellowstone's largest and most tourist-populated spring during the summer busy season.
Katie Hirtzel was visiting Yellowstone National Park and witnessed the bison's death, she said on Facebook. She said watching the episode was "incredibly powerful and moving."
"It was amazing to witness raw nature and the circle of life in front of our eyes like that," Hirtzel said. "It is going to be interesting to see how the park decides to move forward as scavengers are drawn to such a populated area."
Poland said he sees it as a cautionary tale for humans visiting the park. He urged visitors to stay on the boardwalks — which are there for a reason — and not get too close.
"It's amazing to go and visit these places in Yellowstone. They are spectacular," he said. "But this is why it's so important to stay on the boardwalks."
