Can the Cold Really Cause Trees to Explode?

Several forces can cause a plant (or a structure within a plant) to burst. Some of these “explosions” are by design: A number of plants (including milkweed, touch-me-nots, squirting cucumbers, and blue violets) use the pressure built up in their tissues over a period of growth to launch their seeds over considerable distances. Other explosions are caused by external forces, such as lightning strikes. However, did you know that extreme cold can also cause plants—trees specifically—to explode?

As many people know, placing a can or bottle containing a carbonated beverage in a freezer to cool it down on a hot summer day (and then promptly forgetting about it) causes the water in the container to freeze. This phase change from a liquid to a solid causes the water in the container to undergo an increase in volume, and the resulting rapid expansion alongside trapped carbon dioxide places such pressure on the walls of the container that it ruptures.

A similar process can work on trees when environmental temperatures fall rapidly, such as in the wake of cold, Arctic air outbreaks or on cloudless, icy winter nights that follow relatively warm winter days (see also polar vortex). The water found in the sap and vascular tissues within various trees (including ashes, maples, poplars, oaks, willows, walnuts, and beeches) can freeze quickly and expand. At the same time, the tree’s outer bark contracts faster than the cork, inner bark, and other tissues it surrounds, causing mechanical stress to build inside the tree. When the pressure is great enough, this concentrated energy is released as sudden frost cracks that split the tree’s trunk and branches, and these ruptures are accompanied by pops and noises reminiscent of gunshots.

The term explosion (meaning a rapid expansion or bursting out) is still technically correct, although trees do not explode violently like crashed fuel trucks in Hollywood action films—that is, with a spectacular cloud of smoke and flame. Nevertheless, trees experiencing this kind of trauma still pose risks. Splits and cracks in branches and trunks may cause parts of the tree to fall onto power lines, automobiles, and homes, and even upon intrepid hikers in the woods or people strolling on sidewalks. When winter thaws into spring, the splits and cracks caused by the extreme cold also threaten the life of the tree itself, because they provide easy access for insects, fungi, and bacteria to the tree’s tender inner parts.