Something’s happening high in the mountains, invisible to humans—that can dramatically affect our water supply.

It’s a process called sublimation, where a substance goes from its solid form directly to a gas, skipping the liquid state altogether. And water is one of the few substances on Earth that can do this.

It takes 80 calories of energy to melt a gram of ice into liquid water. Then another 540 calories to boil it into gas. But when the environment provides those 620 combined calories all at once, ice can go straight to vapor.

And high mountains are the perfect environment for this to occur, where glaciers and snowpack, exposed to bright sunlight and blown over by warm, dry winds, will often vaporize directly into the atmosphere.

The ice is literally blowing away.

This is important because glaciers and snowpack are nature’s water towers. We depend on their meltwater to fill rivers and our reservoirs, where we use it for municipal water, agriculture and industry.

To calculate the water available to us, scientists analyze the volume stored in the mountains. But sublimation is very difficult to predict, making our water supply hard to measure.

It’s a seemingly simple problem that, especially in places like the American West, impacts millions of lives.

Yet another example of where better data and advancing technology could have a very practical application.