This is a pothole in the Glacier Gardens (Gletschergarten), Lucerne, Switzerland. During the Ice Age, this area was covered by the Reuss glacier. The potholes found throughout the park were created by the strong force of the water as the glaciers melted. The water initially melted on the surface, then seeped through cracks and fissures. The flowing water below the glacier was under intense pressure. As it gained speed, vortices formed and carved large potholes into the sandstone below. The largest pothole in the park is about 9.5 meters deep and 8 meters across.
Josef Wilhelm Amrein-Troller discovered the area in 1872 while digging for a wine cellar. After finding some small potholes, he consulted two geologists who recognized the evidence for Ice Age glaciation. They encouraged Josef to stop blasting the area and preserve the site. Careful excavation began, and a park was opened in 1873.
The sandstone in the park is filled fossils of palm trees and clam shells. Around 20 million years ago, the climate of the Lucerne area was subtropical, with sandy beaches and tropical trees.
Image of a 4-meter-deep pothole, Gletschergarten, Switzerland. Credit Roland Zh