Editor's note: Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week's contribution is from Michael Poland, geophysicist with the U.S. Geological Survey and Scientist-in-Charge of the Yellowstone Volcano Observatory.

Yellowstone National Park is home to an array of “charismatic megafauna” — for instance, elk, bears, bison, wolves, and other large mammals. And as the term “wildlife” implies, these animals are, well, wild. Yellowstone National Park requires all visitors to stay at least 100 yards (91 meters) away from bears and wolves, and at least 25 yards (23 meters) away from all other large animals, like bison and elk.

Despite these well-publicized warnings, stories of people approaching too close to animals, and sometimes being injured, appear every year.

Over the history of the national park, dating back to 1872, two people have been killed as a result of bison encounters and eight from bear encounters (additional fatalities occurred outside the park boundaries). And over the past few decades, there have been an average of a few injuries per year due to human interactions with animals.

During the same time period, since 1872, deaths related to hot springs are more than double those from bears and bison combined — 22 people have lost their lives due to scalding (one additional fatality occurred just north of the park boundary, at LaDuke Hot Spring), and there have been hundreds of injuries. The number of fatalities might be increased by one if the disappearance of a man who was staying at Fountain Hotel, in Lower Geyser Basin, is counted (it is presumed that he fell into a hot spring during a nighttime stroll because no evidence of his disappearance has ever been discovered).

Early visitors at Handkerchief Pool, Black Sand Basin, around 1923. Visitors obviously got a little too close to thermal features back then.

The first reported hot-spring death was in 1890, while the most recent occurred just one year ago, on July 31, 2022.

Perhaps the earliest known incident of injury caused by a hot spring occurred in 1870. Truman Everts, an explorer who became separated from his companions, ultimately survived 37 days in the wilderness before he was discovered and rescued. During his ordeal, he slept near a hot spring to keep warm and was, perhaps ironically, scalded on his thigh by a burst of steam.

Everts’s injury is typical of hot spring incidents — it is the temperature that causes the harm. Although some hot springs are slightly acidic, the acid is not concentrated, but rather is similar in its acidity to orange juice and not something that could dissolve body parts. But many of the hot springs in the park are in excess of 66 °C (150 °F), and some are hotter than 85 °C (185 °F). Especially at those elevated temperatures, just seconds of exposure can cause second- and third-degree burns. When a large percentage of the human body is so scalded, survival rates are low.

While most injuries and fatalities due to hot springs in Yellowstone National Park have been accidental, with people falling into springs they were not aware of, at least one death and numerous severe injuries have been a result of off-leash dogs jumping into springs, and their owners trying to save them. Although dogs are allowed in Yellowstone, they must always be on a leash and are never permitted on trails. This policy is to not only prevent dogs from interacting with wildlife, but also minimize the risk that a dog will jump into a thermal pool — after all, how could a dog be expected to know the extreme temperature of a Yellowstone hot spring?

Some of the hot-spring fatalities sparked lawsuits against the National Park Service, with the family members of the injured and deceased arguing that there should be more warning signs or safety improvements to boardwalks. One such incident, in 1970, led to increased funding for safety programs in the National Park Service, as well as more warnings distributed to park visitors.

Crested Pool, in Upper Geyser Basin near Castle Geyser, was the site of a hot-spring fatality in 1970. Geyser Hill is in the background, and Old Faithful is the steaming feature in the background at the right/USGS, Mike Poland.

Ultimately, the lesson to be learned from past experience is to respect the Yellowstone landscape and everything it contains —   bears, roaring rivers, steep cliffs, and, yes, hot springs. While large animals might seem a more obvious hazard, thermal waters are a far more frequent cause of death and injury in Yellowstone National Park.

(Acknowledgement: Information about fatalities and injuries in Yellowstone National Park, including those associated with hot springs, is well documented in Lee H. Whittlesey’s book Death in Yellowstone: Accidents and Foolhardiness in the First National Park.)