New Research Highlights the Importance of Sublimation for the Rocky Mountain Snowpack
In a year of historic snow drought for the region, a study in Geology shows that climate change can impact the rate that snow disappears into the atmosphere
This past winter, the Rocky Mountains experienced a historic snow drought, a worrying development for the tens of millions of people in the arid American West who depend on snowmelt for water. Now, a new study in the journal Geology investigates the geologic history of a surprising process that might be making the problem even worse: sublimation, the process by which frozen water transforms directly into water vapor, skipping the liquid phase altogether.
“We all see the effects of sublimation when we go to the freezer and pull out the ice cube tray,” says Jeffrey Munroe, a geologist at Middlebury College and the University of Innsbruck and lead author of the study. “We swear we made ice a few weeks ago and yet the tray is empty or the ice cubes are half gone.”
In the Rocky Mountains, sublimating snow means that less ice melts to water that makes it into the reservoirs and rivers people depend on.
Munroe and his co-author, Christoph Spötl, studied a cave ice deposit in northern Utah and found evidence that from about 6,000 to 600 years ago, the disappearance of the winter snowpack due to sublimation systematically increased from about 30% to 45%. While this record doesn’t necessarily show how sublimation might impact the snowpack in this or future years, it does demonstrate the magnitude of the process in the long term and how its impact can vary over time.
The ice in Bear Ice Cave forms when melting of the seasonal snowpack saturates the ground in the spring. Because the floor of the cave stays below freezing year-round, water dripping into the cave from the surface freezes and forms ice. During the rest of the year, the soil is too dry for water to make it to the cave, which means the ice matches the composition of the snow at the end of the winter.
“It sounds improbable,” says Munroe, “but if the geometry of a cave is right, cold air just sinks down into it in the winter and refrigerates it.” In the summer, warm air can’t sink into the depths of the cave, allowing subfreezing temperatures to persist even during warmer months. Nonetheless, cave ice is disappearing fast in a warming climate. Munroe says scientists like himself feel an urgency to study these ice accumulations before they’re gone.
During his first visit to the cave, after descending through an area filled with loose rocks and debris, Munroe noticed his footing was becoming slippery. Eventually, the floor of the cave turned into a steep, icy slope that required ropes to traverse. Then, “all of a sudden you turn around and you’re looking at this impressive cliff of layered ice,” says Munroe. “Geologists love anything that’s layered. You see layers and you’re like, ‘Okay, now we’ve got a story.’”
In this case, that story came from the isotopic composition of the ice, which comes from the melting snow above. Over the duration of the record, the ice became isotopically heavier, meaning the relative proportion of hydrogen and oxygen with an extra neutron increased. Sublimation from the snowpack preferentially removes the lighter isotopes, which turn into water vapor more easily, leaving the remaining snow isotopically heavier. After ruling out other plausible explanations, Munroe and Spötl concluded that an increase in the effectiveness of snow sublimation over time was the most likely driver of the long-term signal they observed in the ice.
Munroe hopes this study highlights the importance of sublimation and helps policymakers better plan for future snow droughts.
“Sublimation is often just ignored,” he says, “and yet any water manager is going to sit up and take notice if you tell them half the snow that falls in winter might just go back into the air, and that value could change over time.”
Citation: Munroe, J., Spötl, C., 2026, Stable isotopes in cave ice reveal Holocene changes in mountain snowpack sublimation; Geology: https://doi.org/10.1130/G54328.1
About the Geological Society of America
The Geological Society of America (GSA) is a global professional society with more than 18,000 members across over 100 countries. As a leading voice for the geosciences, GSA advances the understanding of Earth's dynamic processes and fosters collaboration among scientists, educators, and policymakers. GSA publishes Geology, the top-ranked “geology” journal, along with a diverse portfolio of scholarly journals, books, and conference proceedings—several of which rank among Amazon’s top 100 best-selling geology titles.
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