John Seiler was walking around Virginia Tech’s campus with his students on Thursday morning when something stopped them in their tracks. It was a pretty cherry tree with an unusual jagged scar running along its trunk.
Seiler, a professor and tree physiologist at the university, quickly realized that the damage was the aftermath of what was being dubbed on social media as a “tree explosion.”
The tree “broke due to the cold,” he said.
As more than half of the United States braces for a powerful winter storm, some meteorologists are warning on social media that such “tree explosions” are possible.
But while heavy snow, ice and bitter cold can wreak havoc on trees, Seiler says one important thing must be clear. That means the trees aren’t actually exploding, at least not in the way the word suggests.
What some people call a “tree explosion” is what scientists call a “frost crack,” Seiler said.
It occurs when the temperature suddenly drops or the trees do not have time to adapt to the cold and the sap and water inside begins to freeze.
“Water expands when it freezes, and this can typically happen when temperatures drop very quickly,” said Doug Aubrey, a professor at the University of Georgia’s Warnell School of Forestry and Natural Resources.
This expansion puts a lot of pressure on the bark and wood, sometimes causing it to crack or split, producing a loud impact sound similar to an explosion.
“It sounds more like a gunshot, a really loud cracking sound,” Seiler said. “Sometimes you rush to buy a cold Coke and you put it in the freezer and forget about it and the can breaks, right? That’s what’s happening to the tree.”
The National Forest Foundation says there are “numerous historical and current observations” of trees exploding due to extreme cold.
Seiler said this type of event is not necessarily dangerous to passersby or the tree itself.
“It’s going to be noisy, but it’s not dangerous. There’s not going to be any wood flying into the area,” he said. “And for a tree, when it splits like that, it doesn’t kill it. … But because it splits the bark, insects can get in there, or infections like fungi and bacteria can kill it.”
Additionally, Aubrey said, “If the bottom of the stem freezes, the entire tree can die, but many trees are able to grow new stems from underground buds, so that also varies by species. If a freeze occurs on a branch, perhaps everything on that branch will die, but the tree will survive.”
Aubrey warned that during storms, the weight of ice and snow increases the risk of heavy branches falling from trees. Heavy tree branches can cause harm to homes, cars, and even people.
“The size of the tree will determine what kind of impact it will have,” Aubrey said.
“Pine trees with long leaves can accumulate more ice than pine trees with long leaves or short needles,” Aubrey says. “In terms of branch breakage, larger trees with more open growth tend to have larger branches and leaf areas compared to dense forests where trees are crowded together.”
Seiler agreed that people should be more concerned about large amounts of ice accumulating on trees, which can cause branches to fall and tree tops to break off.
“When you have thick ice and wet snow, you don’t want branches falling on your head,” Seiler says. “It’s very, very dangerous.”
