Can severe cold cause exploding trees? Kind of. They’re frost cracks

As Wisconsin and much of the upper Midwest prepares for rapidly dropping subzero temperatures, some viral social media posts warn people to watch out for “exploding trees.”

The phenomenon, while bizarre-sounding, is real – kind of.

Bill McNee, a forest health specialist with the Wisconsin Department of Natural Resources, said it’s not uncommon for a sudden drop in temperature to cause “frost cracks” in trees. These longitudinal cracks can run the full length of a tree and are accompanied by a loud “bang,” according to the DNR.

McNee said frost cracks occur because the thick sap inside a tree freezes at a colder temperature than water, and usually stays liquid even when temperatures are well below freezing – a state known as “supercooling.”

“It’s going to get cold enough that this sap may actually finally freeze. And when it does that, like ice cubes in your freezer, they expand very quickly,” McNee said. “That just creates a lot of physical pressure that can lead to the frost cracking appearing suddenly, branches can fall off, and people hear this really loud crack from their tree, almost like it’s a gunshot.”

Another factor that can lead to frost cracks, according to the DNR, is that when temperatures drop suddenly, the exterior of a tree can get much colder than a tree’s inner wood, causing the cell of the tree’s bark to shrink and lead to “unequal contraction” between the tissues of the tree’s exterior and interior.

McNee said it would be extremely rare for a tree to fully explode due to frost cracking; usually, the crack becomes part of the tree.

But while rare, tree explosions can happen, he said.

“I’ve never seen the damage of it, but from what I have seen and what I read online is that it is rare for there just to be so much pressure that is suddenly released inside this tree that it almost does explode,” McNee said.

Frost cracks are most likely to occur in thin-barked trees like maples, lindens and sycamores, but can happen in other species, according to the DNR. McNee said any tree that has sap could have frost cracking in the right conditions.

Frost cracking is common for many trees every few winters, and some trees adapt by dehydrating themselves before winter, making it less likely for physical damage to occur, McNee said. For most trees that do get a crack, the living part of the tree typically heals over the “wound” over time, he said. However, a crack can expose a tree to fungal infection or decay, which could lead to the tree dying.

Mcnee advised anyone who sees a severe crack in a tree to consult an arborist to evaluate if the tree is a safety hazard. Severe frost cracking could cause trees to fall.

Benjamin Sheppard, a meteorologist with the National Weather Service in Milwaukee/Sullivan, said the temperature likely needs to get to minus 20 degrees or lower for trees to being cracking. In Milwaukee, the lowest temperatures will likely be minus 14 on Friday, Jan. 23 and minus 11 on Saturday, Jan. 24 – still extremely cold, but above that minus 20-degree threshold, Sheppard said.

Maia Pandey contributed to this report.

Contact Kelli Arseneau at (920) 213-3721 or [email protected]. Follow her on X at @ArseneauKelli.

This article originally appeared on Milwaukee Journal Sentinel: Can severe cold cause exploding trees? Kind of. They’re frost cracks

Reporting by Kelli Arseneau, Milwaukee Journal Sentinel / Milwaukee Journal Sentinel

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