Wednesday, January 22, 2014

Adirondack Deep Freeze: Groans, Snaps, and Booms

winter-injury5When temperatures dip well below zero Fahrenheit, especially if they fall precipitously, things pop. Wood siding creaks. Frozen lakes and ponds emit ominous groans, snaps, and booms that reverberate through the ice. If soil moisture is high and frost is deep, even the earth can shift in a harmless localized cryoseism, or “frost quake” that produces a nerve-rattling bang.

If you live in a wooded area, you’ve probably heard trees popping and cracking during a deep freeze. It’s an eerie sound on an otherwise still night. Native peoples from northern regions were very familiar with this sound, and some even named one of the winter months in honor of it. The Lakota call February cannapopa wi, ‘moon when trees crack from the cold.’ The Arapaho consider December the tree-cracking time; for the Abenaki, it’s January.

I once found a reference in a novel to exploding trees. In the book, a lost teen boy survives a northern winter that’s so cold trees explode into smithereens. I’d lived through winters with minus-40oF temperatures but had neither seen nor heard of exploded trees. What did this author know that I didn’t?

After poring through scientific journals, I realized this: fiction is sometimes, well, fictional. As I thought, trees don’t blast themselves to bits. But since that first reference I’ve encountered the exploding-tree myth a number of times. So what does happen when trees go ‘pop’ in the night (or day)?

As we all know, when water freezes, it expands. Luckily, sap is not pure water. It’s endowed with antifreeze in the form of sugars, and, to a small extent, dissolved minerals.

The more sugar (or any solute) that’s mixed with water, the lower the freezing point becomes. This is due to something known as the “Colligative Property of Solutions,” as you no doubt recall from General Chemistry. (Actually it’s just as well to forget such terms; they clutter one’s head and make it harder to keep track of appointments, car keys and coffee cups. It’s the basic idea that’s important.)

There comes a point, however, when even sugar-fortified sap will freeze and expand. This may rupture the bark of a tree, resulting in an audible crack as well as a visible one. In many cases frost cracks close with no long-term ill effects, but sometimes they do become perennial.

Since it’s a weak point, a frost crack will pop open in cold spells. Then each spring and summer the tree makes callus tissue in an attempt to grow over the injury, resulting in a raised lip along the seam. Such trees have reduced timber value and an increased potential for decay to set in.

There’s nothing one can do for frost-cracked forest trees in terms of prevention or treatment. You can protect young landscape and fruit trees, though, with light-colored trunk wraps, or even a coat of interior-grade white paint, on the lower trunks. Wraps should be removed promptly in spring, and cracks or wounds should never be coated.

In truth, trees do explode occasionally—if someone has placed explosives in them. A friend of mine contracted with the US Forest Service in Oregon in the 1980s to create habitat for cavity-nesting birds. He climbed large spruces and firs, drilled a hole in the trunk halfway up and inserted dynamite, which was later detonated. I’m pretty sure he preferred to do this work when it was not below zero.

Photo: Winter tree injury, left: Joseph O’Brien, USDA Forest Service,; right: Robert Anderson, USDA Forest Service,

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Paul Hetzler has been an ISA Certified Arborist since 1996. His work has appeared in the medical journal The Lancet, as well as Highlights for Children Magazine.You can read more of his work at or by picking up a copy of his book Shady Characters: Plant Vampires, Caterpillar Soup, Leprechaun Trees and Other Hilarities of the Natural World

7 Responses

  1. dave says:


    The last few nights it has been like shotgun blasts going off in the woods around us.

    Boom! A few minutes later, Boom! from another direction.

    Startled me quite a bit for the first few times… the dogs too.

  2. Cloudsplitter says:

    Exploding trees can mean several things. In my experience I have seen “exploded” bark shot out ten to fifteen feet from a tree after a frigid night. Definitely not fiction. Have not seen trees shattered.

  3. Paul Hetzler says:

    Cloudsplitter, do you recall from what species the bark shot out, and how large the fragment was? Thanks!

  4. Charlie S says:

    This is not relative to the above but I thought about it as I was reading.At least twice over the years I have heard a snap when in the quiet woods,and turned to witness a hefty limb falling to the ground from above,then a thud as it came to the ground.What are the odds?

  5. Wally says:

    Very interesting article. Thanks. I’ve experienced this but never saw an article or photos. I also have heard loud cracks at night while camping in the woods, away from roads and people, in warmer weather. What’s going on then?

    • Paul says:

      Wally and Charlie S above. I think that these are likely just trees falling to the ground when they finally reached their breaking point. It does not necessarily come with wind of some other pressure. We had a very large old dead tree fall behind our camp this past summer on a quite windless night. What a crash! Charlie I have seen a number of branches fall on calm days maybe this isn’t all that rare to be there when it happens? But maybe it is?

      I once found a tree that had fallen on and killed a white tail fawn now that is a bummer of a spot to be standing!

  6. Running George says:

    I’ve heard more loud pops in the night in the last two weeks than I ever remember hearing. It’s been very cold but maybe it’s because I don’t sleep as well as I used to.

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