formation of black ice
Before we turn to the current situation on the Upper Engadin lakes, we will briefly discuss the freezing process of lake surfaces.
Lakes freeze first on the surface, which is due to the special properties of water. Water reaches its highest density at four degrees, not when it reaches the freezing point, as is the case with other liquids. This means that the entire volume of the lake must first be cooled down to 4 degrees. Once this has been achieved, only the water near the surface needs to be cooled further, as it does not sink any further due to its lower density. While the water at the bottom of the lake remains at 4 degrees, the temperature at the surface quickly approaches freezing point. If the surface temperature falls below 0 degrees, the water begins to freeze.
If no precipitation falls during the days of freezing, black ice forms. The calmer the lake surface (i.e. the less wind and water current), the smoother, more uniform and transparent the resulting ice surface is.
Black ice on Lake Sils Fractures can provide
qualitative information about the thickness of the ice. (Photo: A. Hostettler)
Late freezing of the Upper Engadin lakes
A thin layer of ice often forms on the larger Upper Engadine lakes romania phone number library in the first half of January. While Lake St. Moritz and Lake Champfèr usually freeze over in December, Lake Sils takes a little longer due to its size. The latest complete “lake freeze” is usually observed on Lake Silvaplana. This is because the lake is significantly deeper over large parts than the lakes mentioned above.
Relief map of the Engadin Lake District
Relief map of the Engadin Lake District. (Source: map.geo.admin.ch)
The decisive factor for freezing is the accumulated time unusual christmas traditions during which the air temperature is significantly colder than the water temperature. Unlike lakes in the Central germany cell number Plateau, in the cold Engadin the cooling in October is already decisive.
Last year, the whole of October was significantly too warm. After a somewhat colder start to December, another sustained and significant period of mild temperatures followed at the end of the year. Accordingly, the two larger lakes formed ice much later this winter. A larger area of ice was not observed on Lake Sils until January 18th.
Deviation of the temperature (daily average) in Sils-Maria. The weather station is located between Lake Silvaplana and Lake Sils.
Deviation of the temperature (daily average) in Sils-Maria. The weather station is located between Lake Silvaplana and Lake Sils. (MeteoSwiss)
Slow freezing of Lake Sils
When a lake begins to freeze over, it usually doesn’t take long for a solid layer of ice to form. Often, even a handful of cold, windless days are enough. This year, things are a little different. On Lake Sils, there are still open patches after more than two weeks.
The SRF report (see link below) reported on the extraordinary situation. The long period with sometimes strong northerly winds may be one reason for the hesitant freezing.