YELLOWSTONE NATIONAL PARK — Got a burning question about the world-famous thermal features found in Yellowstone National Park (YNP)?
Most visitors do. Yellowstone Volcano Observatory Scientist-in-Charge Michael Poland and interpretive ranger Mindy Dottellis collaborated on a recent Caldera Chronicles installment to answer some of the visitor questions that arise most often (besides the No. 1 question: “Where is the nearest bathroom?”).
Water temperature and acidity
“The most common questions across all of the park’s thermal basins are about the temperature and acidity of the water,” Poland and Dottellis noted. According to them, these answers vary by area. They note that Norris Geyser Basin is the hottest thermal area in YNP, with a temperature of 459°F found approximately 330 meters below the surface. Mammoth Hot Springs, on the other hand, is on the cooler side, with max. water temps measured at 163°F since the water has traveled farther from its heat source.
In terms of the acidity, Poland and Dottellis sort the thermal areas into two categories: acidic or neutral. Areas full of geysers and jewel-toned hot springs tend to be neutral, and areas with bubbling mud pots and gas vents are acidic (think of the rotten-egg smell). The major outlier is Norris Geyser Basin, which is home to neutral and acidic features; Steamboat Geyser is neutral, and Echinus Geyser is acidic.
Boardwalk logistics
Another common question from park-goers: How do the boardwalks get built over the fragile and dangerous thermal ground?
“Designing infrastructure that can be safely installed and stand up to Yellowstone’s unforgiving environment is challenging,” the column states. “Geologists map out safe areas for boardwalks based on thermal surveys, but the paths sometimes must be moved because of changes in hydrothermal activity.”
For example: In the summer of 2024, a hydrothermal explosion in Biscuit Basin destroyed parts of the boardwalk. As the park monitors continued activity in the area, the boardwalk might have to be rerouted.
Wildlife
Humans are not allowed to step on the park’s thermal features, but wild animals have free rein to tread wherever they desire. But does the hot ground ever harm them?
“While they mostly avoid the hottest water, animals occasionally make mistakes and fall into thermal pools,” the columnists wrote. “Most animals avoid drinking thermal water, which can be toxic, but they still eat plants that have high amounts of silica and other compounds derived from thermal water. This can contribute to unhealthy teeth, and animals that live mostly in thermal areas tend to have shorter lifespans than those that live outside thermal areas.”
Predicting geyser eruptions
Some of the park’s geysers are as reliable as an alarm clock, making some visitors curious about the science behind prediction calculations. Poland and Dottellis explain that eruption timing can often be determined based on the preceding eruption.
“At Old Faithful Geyser specifically, a shorter-than-usual 2-minute-long eruption means that the next eruption may occur after about 60 minutes, whereas the more common 4–5-minute-long eruptions are followed by a quiet interval of about 94 minutes, give or take about 10 minutes,” they wrote. “Because of this, it is not possible to forecast eruption times more than one eruption in advance.”
