Friday, February 18, 2011

Snow Rollers

Snow Rollers

 While riding through Yellowstone National Park last month, I spied numerous small snowballs that had tumbled down the hill along the side of the road.  On closer look, they were like nothing I had ever seen before. 
"Stop the snow coach!" I blurted out and the nine of us piled out of the snow coach to spend some time photographing these curious snow formations.
I coined them "rolling bagels," since many looked like circles with holes in their center. 
Snow Doughnut
Others were rolled tightly, resembling icy cinnamon rolls...And when back lit, their coils just glowed!  During the short time we were stopped, none of us ever saw one in motion. They were haphazardly scattered along the hillside and stopped in their tracks where gravity had decided to give up on them.  
Working ALL Angles
After returning home I searched the Internet to learn more about these unusual snow formations.  I learned that they are officially called "snow rollers," or "snow doughnuts."   If they form in a wider shape, then they might be called "snow bales" or "snow logs."  Once the initial "seed" of the roller is started, it begins to roll. It collects additional snow from the ground as it rolls along, leaving a trail behind it.  
 According to, the following conditions are needed for snow rollers to form: 
• The ground must be covered by a layer of ice to which snow will not stick.
• The layer of ice must be covered by wet, loose snow with a temperature near the melting point of ice. 
• The wind must be strong enough to move the snow rollers, but not strong enough to blow them too fast.  (this condition describes snow rollers or snow logs on flat ground)
• Alternatively, gravity can move the snow rollers as when a snowball falls from a tree or cliff, lands on steep hill, and begins to roll down the hill. (This is the type of snow roller we saw...)
Because of this last condition, snow rollers are more common in hilly areas.  However, the precise nature of the conditions required to form snow rollers still makes them a very rare phenomenon. In fact, says "Many professional meteorologists go their whole lives without ever seeing this unusual phenomenon." 
Crash and Burn
How fortunate we were to be in the park during those special weather conditions in order to have seen and photographed these mysterious snow rollers!

To see more images made on my recent Yellowstone trip, please visit my  National Parks and Monuments collection.

1 comment:

  1. Fascinating! We experience snow rollers here in Ohio last night... they are all over the place!