What are the sounds coming from this frozen Swiss lake?

Surrounded by snowy mountains, Lake Sils is the biggest lake in the Engadine Valley in the Swiss Alps. The lake surface of four square kilometres is currently covered with a 18cm of ice, and the frozen water creates strange noises that mystify and captivate those passing by. 

Because of temperature differences from above and below the ice layer, walking around and skating on the lake becomes a mystical experience. The cracking of the ice releases deep loud sounds which seem like they come from outer space. However beautiful, the natural phenomenon is temporary: as soon as the ice is covered in snow, the lake’s “singing” will be muffled.

The ice cracks are not a threat to the skaters who have been enjoying the natural ice rink, although they go on the ice at their own risk. Not far away, at the entrance of the valley, another frozen lake will soon be in the media spotlight: the St Moritz lake is hosting the Youth Olympic Games speed skating competitionExternal link, provided the ice remains in good condition. (SRF/swissinfo.ch)