06/12/2026
Volcanic rock? In Virginia?
Although Virginia no longer has volcanoes, hundreds of millions of years ago this place experienced intense volcanic activity. More than 500 million years ago, as the supercontinent Rodinia broke apart, lava spilled out between the tectonic plates and helped form the rock that composes the Blue Ridge Mountains today. This lava solidified into an igneous rock called basalt. Basalt crystalizes, forming hexagonal columns. Devil's Tower National Monument consists of the same material. You can see this crystal formation, known as columnar jointing, on the Compton Peak Trail (mile 10.4 on Skyline Drive) and a smaller example appears on the Limberlost Trail (mile 43). Deep burial underground once covered this rock, but tectonic plate collisions during the formation of Pangea pushed it up and shaped it into mountains.
You can still see the columns, but this rock no longer consists of basalt. Millions of years of heat and pressure buried the rock underground and transformed it into metabasalt, a type of metamorphic rock. Specifically, geologists call this metabasalt Catoctin Greenstone, which stretches as far north as Pennsylvania. Although basalt doesn't really exist here anymore, the columnar jointing reveals much about the geologic history of Shenandoah National Park.
Image: The underside of a large rock formation made of hexagonal green columns.
