The Almsee lake near Grünau in the Almtal valley belongs to the Salzkammergut region of the European Alps in Austria and is an idyllic mountain lake at the northern foothills of the Totes Gebirge mountain range, which is up to 2500 meters high. Totes Gebirge translates to “dead mountain range” and describes its rugged, barren, waterless and therefore unvegetated rocky landscape. This appearance is due to the limestone that builds up the mountains. Rainwater binds small amounts of carbon dioxide and washes it out of the atmosphere as light carbonic acid. This carbonic acid is able to dissolve lime. Over millions of years of steady work, rainwater is able to dissolve entire mountain ranges this way.
Through fractures and fissures in the rock, the water penetrates into the inner mountains and, over time, depressions become cavities and gullies. This creates an extensive network of underground rivers and cave systems where rainwater percolates and drains away. Such landscapes are called karst. The limestones formed about 230 million years ago in the warm shallow waters of a long-vanished ocean called the Tethys, which at that time opened up into a world ocean. We can easily visualize the lagoon and reef landscapes of that time, because they certainly had similarities with today’s Great Barrier Reef in northeastern Australia and the island world of the Bahamas and Florida. Due to the mountain building of the Alps, these sedimentary layers of limestones, up to three kilometers thick, were uplifted and henceforth formed by the rainwater.
The water that seeps into the mountains comes back to the surface through springs that feed the surrounding lakes, including Almsee. The 589 m high lake is poor in nutrients, but with its strongly structured vegetation belt and boggy siltation zones it offers an ideal habitat for many animal and plant species. The lake, which is 2300 meters long and 700 meters wide, is on average only two and a half meters deep, and its numerous springs lie at depths of up to nine meters.
The Almtal was formed by the Alm glacier during the last ice age. About 13,000 years ago, during the end of the Ice Age, a large rockfall occurred here, blocking the valley exit, whereupon Almsee was dammed up. The once much larger and deeper lake became smaller and shallower over the course of time due to the influx of debris from the Totes Gebirge. In particular, torrential rains and the melting of the snow add considerable amounts of rocky debris into the lake. In the area of its boggy siltation zone, where this photo was taken, the lake is just 50 cm deep.
Almsee is often enshrouded in dense fog. This is due to the cool and moist air that flows in from the mountains just six kilometers away. When this air meets the warmer air above the lake, a layer of fog forms. This is especially the case in autumn, when the valley cools down considerably on cold and clear nights and a lake of cold air forms over the relatively warm water. Then dense fogs move over the lake and change the sight of the lake from minute to minute. Together with the colorful autumn leaves, the dawn creates enchanting fairytale-like moods. In the moments when the fog fades out the foreground and background, the marshy siltation zone with the adjacent forest looks like a floating landscape where the ancestors have found their homeland.
