Mystical Black Ice

What are the conditions for the glittering waters to turn into dark, sparkling ice surfaces?

It is common knowledge that water freezes at 0 degrees. A look in a physics textbook will help you to find out, as it reveals that water has its highest density at 4 degrees. In other words: water is heaviest at 4 degrees. As soon as autumn cools the top layer of water in the Engadin lakes to 4 degrees, it sinks and pushes warmer water from the depths to the surface. In order for a lake to freeze, the entire volume of water must first settle at a temperature of 4 degrees. Only then can the top surface of the water continue to cool down without sinking. If the air temperature remains around freezing, the water on the surface slowly begins to turn into a layer of ice. The exact duration of the freezing process therefore depends not only on the number of cold days in autumn and winter, but also on how deep a lake is. The deeper a lake, the longer it takes for all the water to circulate and reach 4 degrees. For the Engadin lakes, this means that the Lago Bianco reservoir on the Bernina Pass is always the first to freeze over completely, followed by Lake St. Moritz and the smaller Lake Champfèr (Lej Suot) - normally as early as December. For Lake Sils, it takes a little longer due to its size and slightly more exposed location, as the wind can also stop a rapid "lake freeze" or literally blow away the freezing process. The last to freeze is usually Lake Silvaplana, which is significantly deeper than the other lakes in the Upper Engadin. The fact that the lakes in the Engadin freeze over completely can (still) be observed every year, even in comparatively milder winters. However, an additional requirement must be met for the formation of the mysterious black ice: it must not snow during the days when the ice freezes over.

This is the only way the frozen lake surface remains transparent and gives the Engadin plateau a particularly magical shine for a few days or weeks. This year, fingers crossed for all those who would like to venture out onto the black ice with their skates: For the first time, Lago Bianco is officially opening a defined zone for ice skaters. Alternatively, various prepared lake ice rinks in the Upper Engadin invite you to ice skate, such as the two ice rinks on the Lej da Staz or on Lake St. Moritz.

Symphony of the frozen lakes

The black ice is not only an unforgettable experience for the eyes, for the dark beauty also draws attention to itself with mysterious noises. The ice concert from the depths of the frozen lakes includes loud bangs and cracking, strange bubbling and cracking, and supernatural sounds reminiscent of whale songs. Science also has a simple explanation for the singing lakes. The reason for this natural phenomenon is the changing air temperature. When it gets warmer, the ice on the surface expands; when the temperature drops, it contracts. This causes cracks to appear on the underside of the ice layer that lies on the water. These movements of the ice surface and their breaking up are responsible for the special acoustic effects of the black ice. When it starts to snow, the snow absorbs the sounds and the mysterious music slowly fades away.