From Seabed to Summit
The sandstone cliffs of the Monti della Laga in central Italy are not what they seem. Today they form peaks reaching over 2,400 meters, but they began their existence on a deep ocean floor. These rocks are part of the Laga Formation, a thick sequence of turbidites deposited during the Messinian age of the late Miocene, between 5 and 7 million years ago. A turbidite is the geologic term for the deposit left by a turbidity current—a catastrophic underwater avalanche of sand, silt and clay that flows down a submarine slope.
The setting was the Laga Basin, a deep foreland basin that formed as the Apennine mountains began to rise. Material eroded from the emerging Alps and Apennines was washed into the sea, accumulated on the continental shelf, and periodically collapsed. These slurries raced for tens of kilometers across the basin floor, depositing their sediment in vast lobes. The evidence for these events is preserved in the rock as graded bedding. Each distinct layer shows coarser, heavier grains at the bottom and progressively finer grains toward the top, a record of particles settling from a submarine landslide. Some individual layers are meters thick, showing the immense scale of these ancient events. The total thickness of the Laga Formation reaches up to 3,000 meters in some areas.