Trees Can Explode in Cold

The sound of a loud crack, like a rifle shot, echoing through a silent, frozen forest might not be a hunter. This startling event is the sound of a tree trunk splitting open under extreme cold. Inside a tree, sap is mostly water, which expands as it freezes. When temperatures plummet suddenly, this expansion happens rapidly. At the same time, the outer bark contracts faster in the cold than the inner wood, creating immense tension. The combination of internal pressure from the ice and external tension from the shrinking (Review) bark can cause the wood to fail catastrophically, resulting in an explosive split.

Known as a frost crack, this phenomenon is most common in hardwoods like oak, maple, and sycamore, especially during sudden, deep freezes. Naturalists and writers have long documented the sound; Henry David Thoreau described hearing the "cracking of the trees" in his journals at Walden Pond. While dramatic, a frost crack is not typically a death sentence. It creates a deep, vertical wound that the tree will attempt to heal over in subsequent years, often forming a raised ridge of scar tissue known as a frost rib, a visible reminder of its violent encounter with the cold.