Whether you refer to them as frost cracks or the colloquial exploding trees, they aren't necessarily dangerous. For the Cree, the final moon of the year is called Pawacakinasisi Pisim, or Frost-Exploding Trees Moon." These month names in Native American calendars highlight the ancient history of exploding trees; tree sap has been expanding and cracking bark for at least 3,600 years, according to Outside. On your next winter walk in the woods, pay attention to heavy branches rather than a loud noise indicating frost cracks. As you plan your winter travels, read up on the Farmer's Almanac winter weather predictions for the season before you go.