On Saturday, June 21st, Yellowstone National Park visitors were shocked and horrified to witness a bison slip into part of the Grand Prismatic Spring. Tragically as the bison stumbled to get out of the 192°F waters (just below boiling temperature at that elevation) it stepped into a deeper area and quickly died.
While it’s a rare sight to witness, it’s not unprecedented for animals to fall into hot springs and die. Animal skeletons are visible in many of Yellowstone’s hot springs, like Gentian Pool, Ojo Caliente, and Skeleton Pool. Many years ago an elk calf died after falling into the mud pots in West Thumb Geyser Basin, and an elk skeleton was found in Doublet Pool on Geyser Hill near Old Faithful.
Other incidents may have gone unwitnessed for a multitude of reasons. Animals can feel the heat of thermal areas through their feet or hooves, but they can still make mistakes near hydrothermal features. It’s likely that most of these fatalities take place when an animal breaks through the thin crusts on spring edges.
While it may be shocking, Yellowstone National Park officials will not remove the carcass as such work could cause extensive damage to the colorful bacterial mats in Grand Prismatic Spring and be dangerous to staff. Instead the bison’s body will be allowed to break down quickly in the near-boiling water, soon leaving just bones behind.
It’s a common misconception that all of Yellowstone’s hot springs are acidic and that the water will cause acid burns on contact, dissolving animals and people who fall in. Acidic features like the the fumaroles, mud pots, and frying pans, which are all dominated by the release of acidic gases, do exist throughout the park, but none of them have acid concentrations high enough to burn on contact (though they can cause skin irritation).
Most of Yellowstone’s major hot springs and geysers are actually neutral including nearly all of the geysers and hot springs in the famous thermal basins spread along the Firehole River. what kills both animals and people who fall into the hot springs is temperature, not acidity. Hot springs often sit at or near boiling temperatures, frequently leading to rather quick deaths when exposed.
It’s the heat, not the acidity, that’s led to the requirement for visitors to stay on boardwalks when visiting the thermal areas of Yellowstone National Park. Many injuries and fatalities have occurred when people step off the boardwalk onto the thin crusts that sit at the surface of thermal areas and overlie boiling waters or hot steam, breaking through, stepping on an unsupported sinter ledge, or stumbling into obscure springs.
“Yellowstone is a wild and dynamic place and can be hazardous. Fortunately, humans (and most animals) can recognize and avoid those hazards. So be sure to enjoy Yellowstone’s magnificent thermal areas from the safety of trails and boardwalks, and don’t forget to stay a safe distance from wildlife wherever you may encounter the park’s charismatic megafauna.” – USGS Yellowstone Volcano Observatory
