Frazil ice: Fascinating forest hazard

Frazil ice looks like patches of snow, nestled among the trees. But it's actually a Slushee-esque mixture of ice crystals that form in bitterly cold waters—like the kind that run through Yosemite National Park in early spring. Watching this video, you can see how frazil ice can appear to be just your average slushy creek water, and, the next minute, turns into what looks like solid (if snowy) ground. And then the ground moves.

If you're thinking that it's potentially dangerous, you'd be right. In the video, park rangers talk about the risk of falling through frazil ice into frigid water deeper than your head.

(Thanks, Ferris Jabr)

Strange nature at Boing Boing:

Weird clouds in Hastings, Nebraska

Giant scary sinkhole

Amazing time-lapse of insect-eating fungi

Hilarious science and math jokes!

Setting things on fire for science

Weird life found on Earth ... maybe



  1. Cool. This will go on my list of things to tell people who trot out the chestnut about the number of Eskimo words for snow.

  2. We get pretty much the same stuff in parts of Vancouver, albeit on a much, much smaller scale, thanks to our mild winters and the combination of rain and snow.

    Pretty cool to see what its like on a large scale.

  3. Not to be pedantic, but Yosemite is not what most people would consider to be bitterly cold. Most winter nights are in the 20s and the record low for the park isn’t even below zero F, it’s 6 F, set in 1924.

    1. She said the WATER was bitterly cold. I would say that these streams are about as bitterly cold as water can get and still remain water.

      1. I would suggest that it is super-cooled water, i.e. water that exists at lower than freezing point. It’s not all that uncommon

    2. The lowest temperature recorded in Yellowstone was -66° F / -54° C near West Yellowstone on 09 Feb 1933.

    3. You need to know that podantic refers to enunciantion. so you have used the word in error here. What you meant to soy is you don’t want to reoterate

    4. Apparently, cold is in the shiver of the beholder. An announcer at Monday Night Football last night spoke about the courage of the remaining fans sticking it out in the bitter cold. It was 26F, about 30 degrees warmer than we experienced here in the mountains a month and aEnohin tr half ago!

  4. we see this where i live on the atlantic coast of canada (nova scotia), too – mostly close to the shore and/or in smaller, narrower coves and bays. it doesn’t flow quite like the stuff in the video, but it’s pretty weird to see it rising and falling with the waves – looks like it’s pulsing or breathing, like some kind of gigantic undersea creature. aaahh!!!!

  5. “…so if you can imagine in your mind…” Victoria Mates, Park Ranger

    Well, no, but I can imagine in my pancreas. . .

    1. Now THAT’S funny!

      Because my mind is so active, I’m going to start using my pancreas!

      Still laughing. Thanks. We need more humor in life.

  6. This was awesome! I wish all of our parks could produce something as wonderful as this. If this was within a twelve hour car trip, I’d go this weekend.

    1. That was totally uncalled for! I happen to know this Ranger and she has been crying over the pain and humiliation this semantical slip up has caused her!

      Ok..I really don’t know her and she is likely LHAO as am I.

  7. There used to be a soda machine in the physics building at my college. The cans of soda were kept at the PERFECT temperature, right at the point when frazil ice crystal slurry would appear suddenly after the can was opened and the pressure released.

    LOL – I can’t count how many cans of soda that accidentally exploded in my freezer while recreating the experience.

  8. @6 ill lich; don’t be hatin’ on Victoria Mates, Park Ranger, she’s cute as a bugs ear, and is totally rockin’ that hat.
    Ever notice how sciencey folks often start out their explanations of things with the word “so….”? For instance, Q: How does my pancreas work? A: “so your pancreas secretes two hormones…etc.”
    I’ve noticed it on radio interviews, it’s like a way of speaking a lot of researchers or scientists seem to have. I hear it on NPR all the time.

  9. This happens on some of the creeks flowing out of the Sawtooths that flow over waterfalls on the upper South Fork of the Payette River here in Idaho. Sat on a rock just above the creeks floodplain watching it ebb and flow all morning one spring. Didn’t know it had a name..

  10. Thanks Boing Boing! This post is a perfect example of the reason why I check this site 5x a day.

  11. You don’t need to go to Yosemite to see this. You can find ponds of frazil ice covering every New York City crosswalk not 6 hours after any heavy snowfall.

  12. We get frazil ice on the rivers here on the Canadian Prairies every winter freeze up, but the rivers have deep channels so the water never breeches it’s banks. Having lived my entire life in a very, very cold place, it’s always amusing to me how excited people can get from snow and ice phenomena. Then again, I get pretty excited by pictures of gardens blooming in March, or, you know, hills, so I shouldn’t be surprised that this would be exotic for someone.

  13. I notice a large number of hits on this video compared to the other eight, which are also well worth watching. I’m apologize for posting this long after the boing boing post has left the current home page, but here are links to all the videos:

    1. wildflowers
    2. yosemite falls
    3. wilderness
    4. half dome
    5. snow
    6. maps
    7. tuolumne river
    8. snow line
    9. frazil ice

  14. Oops: “I’m apologize” started out as “I’m sorry” and didn’t fully transition. I wouldn’t have posted the correction, but I completely forgot to thank Maggie Koerth-Baker for the original link.

    Those videos were a beautiful way to get lost for a while.

  15. Thank-you my dear brother for sharing this. As you know I live about 40 min`s from the gate of Yosemite Park. I have never seen this but sure will next year. I didn`t know there was such beaty In my owen back yard. Thanks again and hope you and Toni can stop by next year when you come up here. Love ya Bro…Your Sis Valerie Jean

  16. I do have plans to bless Yosemite with my patronage, but it’s on my list of places for an extended road trip with The Lovely Lady. Because we’d want to put foot to earth around the time this phenomenon occurs, this is invaluable. But it’s also a cool thing to see on video. Thankyou!

  17. This is where to have Christmas.It looks quite magical and transoforming.What mother earth does is so creative.

  18. We stood on that wooden bridge, (back in 1993), didn’t realise what a wonderful sight we would have seen a few weeks earlier, but the park had only just recently opened, we were told. is it open all year round now?

  19. Yosemite is and has always been, as far as I know, open all year around. I’ve been going up since I was 7 years old—I’ve been up there every season—and that’s a lot of seasons but I’ve never seen this. Time to plan another trip.

  20. There is a 3 part movie of yellowstone by some british guy, there’s 3 seasons on video and the winter is “FREE” on amazon video on demand. It is all about the animals and who is top dog during each season, wolf/winter bear/autumn bull elk/summer, the wolf packs and bison are really cool with some great winter video.

  21. Yosemite Valley is quite magical–it draws you in and entices you to return many, many times. Of course, being a seasonal park ranger makes me biased! Victoria was my boss a few years back.

  22. We see this in the Niagara River every year emtying from Lake Erie. Then you can watch it go over the falls

  23. This is an amazing video. Having visited Yosemite only in the summer, this provides a whole new perspective on the beautiful of this national wonder. I was also impressed with all the comments about Frazil in other parts of the U.S. and Canada. What a neat and informative presentation, especially to share with students and grandkids. Thanks.

  24. Stay on high ground in the woods during springtime. You
    never know whats under your feet. Been there done that.


  25. really nice and I like to sit there and look at it all the time
    hardly to find a view like that. really amazing I grow up on the snow during the winter but very nice in summer

  26. Really amazing show, which once again confirms the greatness of pristine nature. Standing next to those processes feel insecure, and their microscopity impossible and unnecessary to intervene in these from year to year, recurring cycles of nature. Everything breathes a primordial force, commitment, self-sufficiency …

  27. Great article/video/info, thanks!
    I used to live in Yosemite, year round, teaching skiing in the winter and never heard of ‘frazil ice.’ Perhaps it had a different name way back then! Must have been in the valley, becuse Badger Pass, the ski area, definitely had snow and freezing weather!


  28. Not to rain on the parade, but I live in Montana and this happens every year in something as small as a three foot wide creek to large rivers- its called “Spring Break-up”. This same phenom happens on paved roads with some regularity, again, during spring break-up. “Fraz-ice” is nothing more than powder snow- ice crystals. We get plenty of it every year in the Northern Rockies, and would be more than happy to acctually share some of it with the rest of the lower 48, especially at the moment, but the stuff melts before we can send it your way:)

  29. How absolutely amazing nature can be if we only take the time to look and appreciate it and treat it with the greatest respect.

  30. Thnnk you Maggie Koerth-Baker for the video. Yosemite during the winter is on my “bucket list” thanks to Ansel Adams and programs like this.
    Methinks those that say “Well, it happens here too” are not listening very well: nowhere does the video indicate that the Frazil Ice is a Yosemite only phenomenon. They just explain what it is and how it does what it do.

  31. Fly Fishing In A Frazil Ice Stream
    by LouSam

    Before attempting to fly fish a frazil ice swollen stream first watch the attached video to understand the special conditions involved.

    Next, take a trip to your local Dick’s Sporting Goods store. You won’t find much in the way of fly fishing equipment at Dick’s. But you will find some special items that you need to fish frazil ice streams that you would never find in any local fly shop.

    Once in Dick’s, go to the weight training section of the store. Select two fifty-pound cast iron dumbbells and several 5-pound, seven-pound, and ten-pound dumbbells.

    Proceed to your favorite frazil ice stream. No need to bring any dry flies as they would just sit atop the floating ice. And trout won’t be rising above the ice, anyway.

    Before entering the frazil ice stream put on your warmest neoprene chest waders. Tie one fifty-pound dumbbell to each foot. The 100 pounds of added weight to your feet is necessary to keep you from being washed downstream in the flow of frazil ice.

    Next, select your favorite nymph and tie it to your tippet. Then tie either a five, seven, or ten pound dumbbell on to your fly line. The additional weight is necessary to keep the nymph down on the bottom where the fish are.

    One side effect is that after several trips to fish frazil ice streams using the dumbbell technique is that you will soon develop a set of forearms like Popeye’s!

    Happy frazil ice fishing!


  32. What An Amazing & Awesome Sight To See! Wow! Beautiful! I Would Love To Email This To My Friends To See.

  33. Thank you very much for posting this with Closed Captioning. It makes life so much easier for me and a lot of other hearing impaired individuals. I really appreciate your efforts on our behalf.

    The story was wonderful and the pictures very beautiful. I had no idea and in future will definitely be considering a visit to Yosemite and other national parks at “unusual” times of year.

Comments are closed.