Sea frost
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As Seegfrörni (pronounced with a long / o /) is defined as the complete course of freezing or Zugefrorensein one in Switzerland lake . Its ice must be so thick that you can enter and cross the entire lake. The highly Alemannic term was included in the Duden dictionary in 1963. In southern Germany and western parts of Austria, the Bodenseealemannic variant Seegfrörne (see Seegfrörnen of Lake Constance ) or the verbal German form Seegefrörne is predominantly used.
While smaller, shallow lakes freeze over in every colder winter, this is a rare natural spectacle in larger lakes that attracts crowds of people to the respective ice surface. The last big Gfrörnen in Central Europe took place in the winter of 1962/63. B. Lake Constance and Lake Zurich were covered by a thick, walkable layer of ice. Some Swiss lakes, such as Lake Brienz or Lake Uri , have never frozen over in historical times.
Emergence
The process of cooling begins in late summer and is promoted by clear nights, snowfall and cold, strong winds; However, the first ice formation takes place more quickly in calm water, since then there is less mixing with deeper, even warmer water. In general, a deep lake takes longer than a shallower one to cool down. However, other factors also play a role, such as warm inflows from sewage treatment plants or adjacent mountains, which reflect the heat of the sun. Since water has its greatest density at 4 degrees Celsius (see density anomaly ), the colder water remains on the surface and the lake does not freeze from above until the lake is colder than 4 degrees in depth. In the depths, the lake hardly cools down afterwards, since convection no longer occurs.
Individual evidence
- ↑ Cf. Schweizerisches Idiotikon Vol. I, Sp. 1315, article Gfrȫr (n) i and Sē-G'frȫrni ; Baden dictionary vol. V, p. 10, article See-G (e) frörne; Hubert Allgäuer: Vorarlberg dialect dictionary. Graz / Feldkirch 2008, p. 1450, article See-gefrörne .
Web links
- A film document about the Zurich Seegfrörni from 1963 NZZ , article from January 25, 2013 (photos, films, memories)
- Information from the Friedrichshafen city chronicle on the Bodensee-Gfrörnen from 1830, 1880 and 1962/63