A cataclysm in the Dolomites
About 12,000 years ago, near the end of the last glacial period, a massive section of the Pomagagnon-Tondi di Faloria ridge collapsed into the Boite River valley. An estimated 0.2 cubic kilometers of rock and debris suddenly slid away, creating a natural barrier across the valley floor. This event, known as the Cortina d'Ampezzo landslide, fundamentally reshaped the local area. The Boite River, its path obstructed, began to back up, forming a large lake in the basin where the town of Cortina d'Ampezzo is located.
Geologists determined the age of this rockslide using a technique called cosmogenic nuclide dating. When rock is exposed at the Earth's surface, it is bombarded by cosmic rays. These high-energy particles cause nuclear reactions within minerals like quartz, producing rare isotopes such as Beryllium-10 (¹⁰Be). The production rate of these nuclides is known, so by measuring the concentration of ¹⁰Be in the surface of the landslide's boulders, scientists can calculate how long that rock has been exposed to the sky. This method provides a precise timeline for when the landslide occurred, placing it at the boundary between the Pleistocene and Holocene epochs.
The dam breach flood
The natural dam created by the landslide was inherently unstable. Composed of a loose mix of unconsolidated rock and soil, it lacked the structural integrity of a solid bedrock formation. As the impounded lake grew larger and deeper, the pressure on the dam increased. The most common failure scenario for such dams is overtopping, where rising water flows over the lowest point of the crest, rapidly eroding the loose material and carving a breach.
Eventually, the Cortina landslide dam failed catastrophically. The breach released the entire contents of the lake in a massive outburst flood. This torrent of water, far exceeding any normal river flow, would have surged down the Boite valley, scouring the landscape and depositing enormous quantities of sediment downstream. Evidence of this ancient flood can still be found in the valley's geology. The landslide deposit itself is visible today as a distinctive area of hummocky terrain, a direct remnant of the massive rock failure that set these events in motion. The entire morphology of the valley south of Cortina was permanently altered by the landslide, the temporary lake, and the subsequent dam-breach flood.