Apart from the constant calving of the glacier which can be observed from a footbridge only 400 meters away, the Perito Moreno has an unusual feature: every now and then the glacier advances and forms a natural dam that blocks the flow of water from Brazo Chico and Brazo Sur. This dam, which breaks months after its formation, originates a rare and spectacular sight, which is patiently awaited by thousands of tourists from all over the world.