Rime Ice Is Nice

February 2, 2005

It was a bluebird day in early January, just after the big New Year’s snowstorms blew out of Mammoth and the Eastern Sierra.
    Even longtime residents of Mammoth were slack-jawed by the beauty the storm left behind, particularly on the west-facing slopes, where rock-hard rime ice coated just about everything, from trees to chairlifts to trail signs.
    This kind of ice certainly isn’t exclusive to Mammoth, but it happens here more than in most places, almost to the point where locals can claim it as their own.
    This isn’t the ice that one normally associates with typical ice storms. Rather, this ice forms from the freezing of super-cooled liquid upon making contact with a subfreezing surface. It forms into beautiful, white crystals that extend outward from the object, the resulting formations growing into the wind.
    This is a very particular kind of ice, caused by the singular and startling fact that water doesn’t necessarily freeze at and below 32 degrees Fahrenheit. As a matter of fact, water doesn’t always freeze as ice even as low as 40 degrees below zero.
    According to Sunny Slopes hydrologist Rick Kattlemann, 48, water needs to have a condensation nucleus to form as snow or rain. This nucleus can be made up of microscopic specks of dust or, in ocean environments, specks of salt. Once a raindrop or a snowflake is formed, it can attach to other raindrops or snowflakes, propagating itself exponentially.
    These droplets are very small. One raindrop, for example, can hold up to a million of these droplets. Without a nucleus, however, the droplets can stay in super-cooled, liquid form well below zero. It’s a little bit like super-cooled fog, called poconip fog around here.
    When these super-cooled droplets hit an object, they immediately freeze into a small piece of rime ice, Kattlemann said.
    “Mammoth Mountain has that marvelous canyon behind it—the San Joaquin River drainage—and the first thing that super-cooled water hits is Mammoth Mountain,” Kattleman said, explaining why Mammoth is a kind of rime capital.

As for Mammoth’s amazing, white formations, Kattlemann said:
    “Rime can occur without snowfall, but when it occurs during storms, then you get that combination of true rime and snow, and the result is really big formations.”