A geologic collision in motion
The Apennine mountains, the rocky spine of the Italian peninsula, are the direct result of a slow-motion collision between continents. The mountain-building event, or orogeny, began around 20 million years ago in the Miocene epoch and continues today. This process involves the Adriatic microplate, a chunk of crust connected to the African plate—subducting, or diving beneath the Eurasian plate. As the Adriatic seafloor descends, layers of sedimentary rock deposited over millions of years in the ancient Tethys Sea are scraped off, folded, and stacked on top of each other.
This immense compression created a fold-and-thrust belt. Geologists use a technique called balanced cross-sections to estimate the scale of this deformation. By conceptually unfolding the crumpled rock layers, they calculate that at least 100 kilometers of the original seafloor has been horizontally compressed to create the mountain range. The highest peak in the Apennines, Corno Grande in the Gran Sasso massif of Abruzzo, reaches an elevation of 2,912 meters (9,554 feet). Its limestone and dolomite composition shows its origin as ancient marine sediments. The main thrusting phase that built the Gran Sasso ended in the Late Pliocene to Early Pleistocene.