Snow Rollers… not your grandfather's whitecaps, unless gramps is an Eskimo! This rare winter phenomenon can occur anywhere in the world if conditions are just right, and the eerie beauty of a meadow covered in frozen white waves is, for those lucky enough to witness them, a rare pleasure indeed!
Mother Nature's Snowmen
Most everyone has enjoyed the experience of making a snowman, and those who have done so know that the easiest way to make one is to start with a small snowball, then roll it in snow until it becomes a BIG snowball. Do this three times, pile the snowballs atop one another, and you've got your basic snowman. Of course, the weather outside has much to do with your success – because the weather determines the texture and consistency of the snow.
(images via: Telegraph UK)
Snow Rollers are somewhat similar to the snowballs used to make snowmen but they are much more dependent on not only the weather, but the condition of the snow on the ground.
See What Condition Your Condition Is In
Meteorologists investigating Snow Rollers have turned up some common factors that seem to be prerequisites for their formation. The snow, for starters, needs to be sticky enough to hold together once the ball gets rolling, so to speak. Referring back to snowman-making, the ideal type of snow is loose in consistency while the "stickiness" derives from an air temperature slightly below freezing.
(image via: C.Atrox)
Ground temperature is important as well – it should also be slightly below freezing in order to provide a little bit of lubrication between the various layers of snow. The most critical of such layers is formed from ice, so that embryonic Snow Rollers can initially break free from their anchoring substrate. This is NOT good, however, if you're in a mountainous area standing downslope. Can you say "avalanche?"
Winter Wind FTW
Now let's talk about wind. Too stiff a breeze will simply shift snow and blow it into drifts. For Snow Rollers to form on a relatively flat ground surface, the wind must be of a certain speed and it has to blow consistently – no gusts, as newly formed Snow Rollers are often delicate.
(image via: Ilmajaam.ee)
Wind can also come into play by shaking clumps of snow off of tree branches or overhanging rocks, cliffs or what have you. If the clump should fall on an unstable snow pack and the wind is blowing just right, Snow Rollers or natural snowballs can form.
A Step On A Slippery Slope
Gravity will sometimes act to assist Snow Roller formation. An inclined surface often needs less of a shove from the wind to get Snow Rollers in motion. Falling snow clumps as mentioned above can also "hit the ground rolling", and end up at the bottom of a valley greatly increased in size.
(image via: Wikipedia)
Now here's something you don't see every day – then again, who'd really expect to? Give nature a slippery surface, add snow, fine tune the temperature and you've got a recipe for twin Snow Rollers. Too cool for school… though not THIS school.
Field Of Dreams
(image via: KATU.com)
Classic Snow Rollers, however, are typically seen on clear, flat fields upon which gravity plays no part. Their creation, propagation and lateral motion is governed strictly by the wind – as well as the aforementioned snow and ground conditions. A newly discovered field of Snow Rollers can look like a meadow scattered with miniature white hay bales – so artificial, onlookers find themselves scouting for footprints of the makers.
Roll Out The White Carpet
(image via: Wikipedia)
There are physical limits to the size of Snow Rollers. You won't see an entire field rolled up like a cheap carpet, for example, as weight and stress conspire to keep most Snow Rollers looking much like rolled-up sleeping bags. The very wide Snow Rollers shown above, photographed in the Giant Mountains of the Czech Republic, are as rare as they are ephemeral.
Snow Rollers also gain weight as they roll, and sooner or later – often sooner – the weight of the Snow Roller combined with resistance from the fresh snow ahead of it counteracts the forces of wind and inertia. The biggest reported Snow Rollers were roughly 2 feet (60cm) in diameter.
The Hole Truth
(image via: Morning Earth)
One salient feature common to most Snow Rollers is the "donut hole" in the middle. One would think that it would be impossible to roll a blanket of something as fragile as snow around, well, nothing… and you would be correct.
Snow Rollers do indeed have filled holes at their inception, however this initial layer of snow is usually thin due to the baby Snow Roller's size, and soon crumbles under the stress and vibration incurred as the Snow Roller picks up speed and snow.
(image via: Enquirer)
Snow Rollers are as delightful as they are rare – the latter accentuating the former. Winter may seem to offer nothing but chills and spills, but rare and special natural phenomena like Snow Rollers provide those lucky enough to witness them an undoubtedly warm thrill. Let's roll!