Holey rollers

By Phil Plait | December 23, 2009 7:30 am

I pay a lot of attention to weird things, and to weird weather. I thought I had heard it all: mammatus clouds, inversion layers, parhelic arcs.

But I can still be surprised! For example, I would’ve sworn up and down that snow rollers — giant rolls of snow that look like huge white Ho-Hos — were fake. But they are, in fact, real. Back in March, Tim Tevebaugh saw some in Idaho and snapped away. I couldn’t believe the photos, they’re so weird, I had to contact Tim. He kindly replied, and gave me permission to post pictures:


There they are, sitting on a plain. Evidently, wind conditions need to be just right, and the snow must be precisely the right consistency. I don’t think anyone has seen them form, but I suspect a small clump of snow gets picked up by the wind and rolls into a snowball. When it gets too big it collapses, starts rolling again, picks up more snow, collapses again, and eventually forms these long cylinders. It’s just a guess, but it seems logical. [UPDATE: several commenters have pointed out that the ball need not collapse to make a roller; I had supposed that happened to help spread the ball out horizontally. I stand corrected!]

Just how bizarre are these things? Here’s another picture:


If you look at the big one on the right, you can see how it looks like a piece of foam that’s been rolled up, a testament to how it formed. It like looking down the maw of the Doomsday Machine from Star Trek. I would love to see something like this as it happened. I’ve not seen anything like it in Boulder, but we’re getting plenty of snow here, and it’s plenty windy here so one day I hope to spot them.

I’m perpetually amazed at the imagination and creative power of nature. Snow rollers! Who knew?

Tip o’ the Frosty magic top hat to James Oberg and my thanks to Tim Tevebaugh for sending me the pictures and giving me permission to post them.

CATEGORIZED UNDER: Cool stuff, Pretty pictures, Science
MORE ABOUT: snow rollers

Comments (60)

  1. bubba

    F***in’ weird, man. So far the only interesting thing happening this holiday season.

  2. Mike

    I dunno, Phil. Those look an awful lot like rolled up sod (or hay) sprayed with a small amount of fresh snow. It might be interesting to see one of those given a swift kick; if it’s really as described, it will disintegrate.

    Though that does look like a dead *cornfield*, it doesn’t appear that there is as much snow on the ground as the “roll” thickness would imply.

    That image is setting off my skeptic alarm. I’m having quite a bit of trouble believing it. Though maybe it’s my California upbringing….

  3. silence

    They’re definitely real. Conditions were right for creating them last winter in Sequoia National Park, so here’s a photo which shows detail of how they form. The cool thing was that because of the sloping terrain, you could start their formation by dropping a little bit of snow, squirrel pee, or whatever, and it would just gather up more and more as it rolled downhill until reaching a flatter spot.

  4. I found this to be strong evidence for the existence of an Intelligent Roller

  5. Sean Tibor

    I could definitely see how this could happen, especially given the likelihood of wind in the open area, the gradual slope of the land, and the right kind of snow. This would have to have enough moisture to stick together, but not so much as to make the snow too heavy to roll. Each of these should leave a trail behind them that is a very elongated triangle, which is caused as snow sticks to the edges of the rolling cylinder, making it grow wider.

    We used to make these all the time when the snow was right and we were too lazy to roll in a circular pattern. I could see how this would happen with wind, a gentle slope and the right kind of snow.

  6. Daniel J. Andrews

    Snow rollers are certainly real. I saw them when I was working on the prairies. I had already heard about them so I was excited to see them at last. The ones I saw weren’t terribly big but who knows, maybe they’d “evolve” and get as big as the ones in the picture if the wind picked up again (actually that dang wind hardly ever stopped).

  7. rob

    another possibly wind powered weird thing is the rocks in death valley that leave tracks behind them.

    i wonder what would happen if one of the rocks and a snow roller collided?

  8. Canada Jeff

    Yup, real. They tend to occur in the wide open prairies of Saskatchewan and Alberta too. They’re rare, but I’ve seen fields full of them a hand full of times in my nearly 40 years.

    Nature’s imagination is far greater than ours.

  9. How many holes are in these “Holey Rollers”?

  10. Fergus Gallagher

    Don’t think you need the snowball to “collapse” to make these. Just push a snowball along and the same shape will emerge.

  11. “Natures imagination is far greater than ours.”

    Oh yeah? Do you think nature could come up with a hot fudge sundae or Lil Wayne?

  12. It’s aliens. I mean, nature can’t do that. Humans could, but WHERe are thE FOoTPRINTS!!One!!!eleven!!!

    The truth is out there.

  13. Haruspex
  14. @ vanderleun:

    Oh yeah? Do you think nature could come up with a hot fudge sundae or Lil Wayne?

    Nature did.

  15. Bad Albert

    Now we know what crop circle pranksters do in the winter time.

  16. Brian T.

    Bets on whether Val Kilmer is rolled up at the center of one of those? (Anyone else remember ‘Willow’?)

  17. @Brian T.

    “You are my sun, my moon, my starlit sky. Without you, I dwell in darkness.”

  18. Chris A.

    Wow, I get to be the first grammar nit-picker on this post? Merry Christmas to me!

    “There they are, sitting on a plane. ”

    While parts of Idaho are flat, indeed, none of it is a true plane. There are however, some plains.

    And yes, a typo: “It like looking down the maw…” is a rare case of an “its” that is MISSING an apostrophe (and an “s” to boot).

    No worries, Phil–I know it can’t be easy cranking out as much scientific goodness as you do, day in, day out. Keep up the good work and happy holidays!

  19. kevin

    i’d say hay with snow. most fields in cow country get rolled up hay as feed for the cattle for the winter. snow on hay = ‘snowroll’.

  20. Annalee Flower Horne

    For some reason, looking at those pictures is making me giggle like a child.

    They really do look like sod bales, but I doubt they’re a ruse. For one thing, such a ruse would leave either footprints or helicopter blowback, and for another, it’s pretty repeatable. Roll a snowball down a steep hill and have a look at it when it gets to the bottom–bam. Spiral.

  21. jeswel

    We had smaller versions in Cincinnati a few years back. We didn’t have enough snow or the great expanses of the prairies but it was awesome to see little miniature versions. I can imagine how with enough space and snow the large ones can be created.

  22. Well, Phil finally got me to comment on something other than
    Hubble results and related. The first paper (that I am aware of)
    on “Snow Rollers”, and I *think* the origin of the term in the
    published literature – but very happy to be corrected in that – was in a
    short Note that appeared in the December 1895 issue of the Monthly
    Weather Review (vol 23, issue 12, p 465). The note begins:
    “The phenomenon of snow rollers was observed by the passengers on the Flint River division of the Flint and Pere Marquette Railroad on December 10. They
    report that in large level fields hundreds of snow balls, some of them of colossal
    size, mere rolled together by the action of the wind. The fields were covered with them.” The rest (worth reading, particulary in the retrospective context of
    contemporary photographs) is here:


    This started a series of reports which appeared sporadically (as did the
    snow rollers) over the next decase:

    (that with the first photograph I had seen in Fig 1)

    I’m an astronomer, not a meteorologist (though for unrelated reasons in
    the past I had published in the Journal of Climate). Part of what I study are ices
    in circumstellar disks – and first came across the above earlier accounts of snow
    rollers a while ago when investigating whether such structures could form
    with methane snow given its properties (the answer is a definite maybe; but
    not [yet] published).

    But, it is clear that water-ice snow rollers on Earth are a natural phenomenon.
    As to “snow angels” , e.g., :
    those obviously must be due to aliens from methane-ice bearing worlds
    who came here to work in a more sustainable medium.

  23. Sam Ley

    Neat photos!

    No, these are definitely a real phenomenon. It is conceptually similar to the “sliding rocks” of the Utah Salt Flats. The flats are, of course, extremely flat, but sometimes you’ll see a rock (maybe grapefruit sized) with a shallow trench behind it, like it has been drug along the ground, but with no signs of disturbance. Sometimes you’ll see hundreds of rocks in an area, all with the same length of trench extending away from their current position in the same direction.

    The claim was that the wind blew them around, but no one believed it, and thought it was a hoax. Turned out the wind theory was basically right, but that it can only happen when there are rare wind storms that bring enough rain to lubricate the flats – the salt crystals on the surface get very slippery, and the wind is able to push these rocks around, I think it has even been filmed.

    Pretty fun stuff!

  24. Doc

    We had some small snow rollers show up in our front yard a few years back. At first I thought some kinds had played a prank, but then I noticed there weren’t any footprints anywhere nearby.

    I knew they were uncommon, but if I’d realized how rare they were I’d have taken pictures.

  25. GT

    They formed on a “plane” or on a “plain” or maybe both, but not an (air)plane?

  26. jtradke

    This reminds me of the Racetrack Playa in Death Valley, where there’s rocks that move every few years, leaving tracks behind them. That wikipedia page has an awesome nighttime panorama of the playa, including the Milky Way in the sky above.

  27. Ken

    These are not at all uncommon….

    While you’re on this theme/topic you might want to consider digging up the bit about rocks & boulders that move “on their own” in some deserts. In Search Of (narrated by L. Nemoy aka Mr. Spock) did a bit on this way way way back. Turns out what happened there was in the rare periods of rain & wind the hard, clay-ish, surface would get wet enough to form a slip plane sufficiently slippery for the wind to blow the boulders along on a thin film of natural lube. Sometimes quite a long way. Later, when the area dries out again there’s the dried out & cracked ground with unmistakable shallow grooves where the rocks traversed (but with no other evidence of footprints, etc. to cause the motion). Because the airflow around other objects causes local wind patterns on the ground to go different directions one might observe a number of rocks that appeared to have moved on their own in multiple different directions at the same time.

    Much much more mysterious & interesting than natural snowballs rolling in the same direction as both the wind & grade.

  28. Erasmussimo

    Some observations: first, it appears that these structures do not strip the snow down to the ground, as is common with anthropogenic snowballs. This suggests the presence of a boundary layer in the snow that facilitates take-up of snow by the roller.

    Second, I am much more intrigued by the irregular snow structures shown in the photos. There are a few baby rollers, but many of those smaller objects are not rollers at all. At first glance we are tempted to interpret them as merely ejecta from the rollers. However, a closer examination reveals them to lack any similarity in structure; with a few exceptions, they appear to be quite irregular in structure. Moreover, some of them do not appear to lie on the path of any of the rollers. It’s difficult to be sure, given the small size of the photos; perhaps I am mistaken. But my physics intuition is intrigued by them.

    Third, the angle of the internal cone inside each cylinder is indicative of the stickiness of the snow. It would be interesting to obtain a distribution of the angles of rollers in the same field and compare it with the distribution of angles of rollers in different situations; a small standard deviation would indicate just how narrow the range of conditions required for creating these rollers is.

    Fourth, estimating from the size of the foreground stubble, the maximum size appears to be about a meter. Is this maximum size a function of wind speed, snow stickiness, or snow density? Probably all three. But note that the maximum size appears to be the same in both photos.

  29. Brian

    For those claiming they are hay bails covered with snow just take a closer look at the side of the snow rollers in the picture – hay bails are flat on the sides. Hay bails are also much more uniform in size and are usually spaced an equal distance apart. Definitely not hay (or sod) covered in snow.

    Really cool though.

  30. Keith Sakatch

    They are real, I remember the year that we had them in my parents backyard for Christmas. Ours were much smaller than the large ones you see.

    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.


  31. Cmdr Awesome

    Having grown up in the Wintery northlands that you folks call “Beerland” and we folk call “Canada,” I’ve much experience with rolling snow (specifically making snowmen.) With that in mind, Phil, there’s really no need for the initial snow clump to collapse during rolling. If you start with a small snowball and roll it in a directly straight line, it will naturally form into a cylinder shape rather than a ball.

    This makes sense when you think about it – the small ball shape penetrates deep into the snow. The bottom of the ball picks up some snow and so do the sloping downward sides. The weight of the ball tends to focus heavily on the bottom of the snowball, which either compresses or knocks off loose snow. The sides of the snowball don’t have that same weight, so the snow builds up more loosely at first, but evens out the sides to form a flat base. After that, the sides pick up snow at the same rate as the bottom and then pack it in tight, until the whole ball is about the same density and pretty much flat cylindrical.

    Also, I think I can see the snow conditions under which that kind of thing would happen. The snow would have to be very fluffy and very light, and very sticky. It’s the sort of thick snow that stacks up thick on tree branches and forms light balls as it falls. In strong winds and with a thin enough snow layer I could easily see it rolling and forming those kinds of structures.

  32. CB

    I dunno… that much snow that is wet enough to stick is going to be heavy. Has anyone done the math to estimate how strong the wind would have to be to make these?

  33. timur

    No, you don’t need to collapse them to get rollers, Phil.

  34. Chris

    You are all wrong. They are called “Sno-Ho’s”.

  35. Chris A.

    @Glenn Schneider (#22):
    Isn’t the reason (water ice) snow can stick together because ice crystals comprise water molecules which occupy more volume than an equal number of water molecules in the liquid state, and the crystals, when crushed, can be forced into the liquid state at sub-freezing temperatures, only to re-freeze when pressure is released (AKA regelation)? Wouldn’t methane need to exhibit the same peculiarity (i.e. having a lower density in the solid phase than in the liquid phase) for methane snow rollers to be possible? Or is there another type of stickiness (van der Waals?) that dominates here?

    (FWIW, I’ve seen snow rollers on snowy mountain slopes that were gravity-driven, as opposed to wind-driven.)

  36. Chip

    Sooner or later we’ll discover that Mars has them too – they’re weird enough. 😉

    BTW – I wonder if anyone has tried to test theories as to their formation by experiment or observation.

  37. CB

    Some rough numbers I found are that a 60 mph wind can exert about 10 pounds per square foot, and a cubic foot of snow can weigh from 7 to 20 pounds per cubic foot. So I guess it is not that hard to imagine a stiff breeze rolling those suckers along.

  38. StarScream

    We used to make them as a kid. They’d eventually get so big you would push your arms through before they’d budge anymore. But I had no idea they were also a naturally occurring phenomenon too.

  39. Grizzly

    @36 I’m not sure, but heck I’m not a snow scientist. It seems that these only occur in specific conditions and my experience with snow is that it has to be at a certain temperature in order to stick together… (snowball snow anyone?)

    Unless there are other factors at work here, I don’t think that snow on Mars would ever be “warm” enough for that. I also don’t think that the wind would be strong enough on Mars.

  40. JB of Brisbane

    “A maw… did you see its paw?” (William Shatner, from an outtake from the Star Trek episode “The Doomsday Machine”)
    What is this “snow” you people keep talking about?

  41. Jason Dick

    Interesting. Those look pretty much exactly like what we would end up with in our back yard when we’d just roll a snowball in a straight line for a while. But given how freakin’ heavy they get at around that weight, somehow I don’t think that this is anything but a weather phenomenon.

  42. molybdenumfist

    Weird to see natural ones. I saw this once when I was at school and we had snow (not too common here Downunder!) People were making snowballs by rolling them down a big hill we had. They ended up as snow logs at the bottom. Nowhere near as well formed at those ones though.

  43. rdpayne

    The tumbleweeds of Christmas

  44. Zyggy

    Another factor to consider when wondering if the wind could push these puppies around is inertia. Especially on a slight downhill incline, the inertia (due to gravity’s acceleration) of a larger, heavier “roll” could be a significantly greater force than the wind could exert.

    In other words: the wind starts the process, then inertia takes over until the gravity/friction slow it to a halt.

  45. Saw the same thing in the field behind my home a year and half ago, ok smaller but the same thing.
    click my name

  46. Stunned

    Uh-oh, Rollers. Bet they got SCMODS.

  47. Plutonium being from Pluto

    Cool! 8)

    Literally. 😉

    @39. Grizzly Says:

    I don’t think that snow on Mars would ever be “warm” enough for that. I also don’t think that the wind would be strong enough on Mars.

    How about on Pluto? 😉

    Pluto has an atmosphere -its even generous enough to share it withCharon in summer – & has nitrogen snow. Would this work there with that?

    Or on Eris (further out not sure if Eris has an atmosphere) or Neptune’s moon Triton or Saturn’s moon Titan which have atmospheres and geological /meteorological activity?

    PS. Merry Christmas eve y’all! 😉

  48. Plutonium being from Pluto

    @ 16. Brian T. Says:

    Bets on whether Val Kilmer is rolled up at the center of one of those? (Anyone else remember ‘Willow’?)

    Indeed I do.

    Actually I remember a trio of them :

    1. the fantasy movie with its eponymous little hero (http://en.wikipedia.org/wiki/Willow_(film) ),

    2. the character in Buffy : The vampire Slayer(http://en.wikipedia.org/wiki/Willow_Rosenberg)

    & for a *really* obscure one

    3. its what Byron called Lyta Alexander in Babylon-5 (http://en.wikipedia.org/wiki/Lyta_Alexander & http://www.midwinter.com/lurk/guide/095.html )

  49. MadScientist

    My first guess would have been rolls of hay in a hoar frost. I’ve never even heard of the phenomenon before.

  50. Zed

    Looks just like round bails covered in snow. No one here in 4H or FFA?

  51. Spectroscope

    I pay a lot of attention to weird things, and to weird weather.

    Even mundane things & mundane weather have their charms & appeal & surprises when you think about them deeply enough! 😉

    @ 53. Zed:

    No one here in 4H or FFA?

    Sorry but I’ve forgotten or never heard – what do 4H & FFA mean / stand for?

  52. Beelzebud

    We had these happen one time here in central Illinois. It was pretty shocking to walk out the front door in the morning and see all of these little rolled up bails of snow. Out of over 30 years of living here, it’s the only time I’ve seen them, so for our part of the world, I’d say it’s a fairly rare occurrence.

  53. 45. aporeticus Says:

    Snow can also form itself into donuts!

    Hmmmm… snownuts!

    54. Spectroscope Says:

    Sorry but I’ve forgotten or never heard – what do 4H & FFA mean / stand for?

    I remember FFA as Future Farmers of America, but don’t remember what the 4 H’s are, but it’s another ‘rural culture’ (farmers, ranchers, etc.) organization… let’s Wiki.. ah: head, heart, hands, and health.

    A Joyous Saturnalia to all!!!


  54. Don Gisselbeck

    Snow rollers (some hollow and some not) often happen on steep slopes from point sources when there is heavy wet powder. I have also frequently started them skiing in spring wet powder. They can get several feet in diameter.

  55. Kristian

    I have actually seen this phenomenon happen… but on a small scale, not big rolls like this but small 1 or 2 inch ones. actually the wind picks up a portion of the top layer of snow which it skims from the surface of the snow, so it starts out as a cylinder. the hollowed out middle is caused by a greater amount of snow surface that is picked up as it rolls. in the photos you can see that there are no foot prints leading to the snow rolls, therefore you can conclude that it is indeed a natural phenomenon.

  56. oops

    We saw these once in southern Ohio in the seventies. They were 2″ to 4″ tall and appeared to be formed by gravity as they were at the bottom of steep banks. The sun melted the thinner centers, leaving just the wider rims, so we called them “snow o’s”.


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