Tree sap is mostly water with sugars and minerals, and like many liquids, it expands when it freezes. Gradual freezes usually don’t harm trees — even if it gradually cools to subzero — but plunging temperature swings cause uneven freezing and internal pressure. This stress can crack the bark and wood, producing what sounds like a loud pop.

Meteorologists are warning that an incoming subzero cold snap comes with an increased risk of "exploding trees." Arborists say it's a real thing that

We have a prairie fire crabapple tree that has very severe splitting in almost all of the major branches. There is some evidence of old bark splits that have healed over that we did not notice until recently. The tree seemed to be slow leafing out this ...