An Ice Age Superhighway
During the Last Glacial Maximum, around 20,000 to 26,000 years ago, the landscape of the Alps was unrecognizable. The average annual temperature was as much as 10°C colder than today, allowing a vast ice sheet to cover the mountain range. One of its most powerful components was the Adige Glacier, a massive river of ice that flowed south through the Adige Valley. At its peak, the ice in the main valley reached a thickness of 800 meters, and in some areas of the central Alps, ice thickness exceeded 2,000 meters. This immense glacier was a dynamic mass; it was a powerful agent of geological change, scraping, sculpting, and transporting rock.
As the Adige Glacier ground its way south from the high central Alps, it quarried enormous blocks of rock from the mountainsides. These rocks, frozen into the base and sides of the glacier, became passengers on a slow-motion journey. The glacier was a continental-scale conveyor belt, carrying its rocky cargo far from its origin. When the glacier reached the lower elevations where the Lessinian Alps meet the Po Valley plain, it fanned out, slowed down, and began to melt. The ice dropped its load of sediment and rock, creating a massive series of ridges called a morainic amphitheater. The Amphitheater of Rivoli Veronese is one of the most significant of these formations.
Alien Stones in a Limestone Land
The Lessinian Alps are primarily composed of sedimentary rocks, like limestone. The boulders left behind by the Adige Glacier, however, are geologically alien to this region. These glacial erratics—named from the Latin errare, to wander—are made of igneous and metamorphic rocks, such as granite, tonalite, and gneiss. Their presence on the limestone hills shows that they came from somewhere else.
Scientific detective work, known as provenance analysis, has traced the origin of many of these erratics with remarkable precision. By comparing the specific mineral composition and texture of the boulders with bedrock from across the Alps, geologists have identified their source. Many of the granite and tonalite erratics found near Rivoli Veronese match the rocks of the Adamello-Presanella massif, a large intrusive igneous body located in the Italian and Swiss Alps, over 50 kilometers to the north. These boulders record the scale and power of the Würm Glaciation, the last major glacial period in the Alpine region. They provide a direct physical link between the high peaks of the central Alps and the rolling foothills of Veneto.