These impressive potholes were formed at the bottom of the glacier by the sheer force of the water. As is still the case in alpine glaciers today, the melt water initially flowed on the surface of the ice before seeping into the glacier through fissures. At the bottom of the glacier the water was under tremendous pressure. As the flow of water gathered speed, vortices with speeds of up to 200 km/h began to form. Within a few years, potholes had been eroded out of the rock. Most of the erosion was done by sand and gravel trapped in the cloudy melt-water flow.