The Almsee near Grünau in the Almtal Valley is nestled in Austria’s Salzkammergut region of the European Alps, at the northern foothills of the Totes Gebirge mountain range, which rises to nearly 2,500 meters (8,200 feet). Totes Gebirge translates as “Dead Mountains,” a name that describes its rugged, barren, waterless, and therefore largely unvegetated rocky landscape. This stark appearance is a consequence of the limestone that forms the mountains. Rainwater absorbs small amounts of carbon dioxide from the atmosphere, forming a weak carbonic acid capable of dissolving limestone. Over millions of years, this seemingly gentle process can dissolve entire mountain ranges.
Through fractures and fissures in the rock, water penetrates deep into the mountains. Over time, depressions develop into cavities and gullies, creating an extensive network of underground rivers and cave systems through which rainwater percolates and drains away. Landscapes shaped by these processes are known as karst. The limestone itself formed about 230 million years ago in the warm, shallow waters of the long vanished Tethys Ocean, which was then connected to the global ocean. We can easily imagine the lagoons and reef landscapes of that ancient world because they likely resembled today’s Great Barrier Reef in northeastern Australia and the shallow island seas of the Bahamas and Florida. During the formation of the Alps, these sedimentary layers of limestone, in places up to three kilometers (1.9 miles) thick, were uplifted and subsequently sculpted by rainwater.
The water that disappears into the mountains eventually returns to the surface through springs that feed the surrounding lakes, including Almsee. At an elevation of 589 meters (1,932 feet), the lake is poor in nutrients, yet its richly structured vegetation belt and extensive marshy siltation zones provide an ideal habitat for numerous plant and animal species. The lake is about 2,300 meters (1.4 miles) long and 700 meters (2,300 feet) wide, but averages only two and a half meters (8 feet) in depth. Its numerous springs emerge from depths of up to nine meters (30 feet).
The Almtal Valley was shaped by the Alm Glacier during the last Ice Age. About 13,000 years ago, toward the end of the Ice Age, a massive rockfall blocked the valley exit and caused Almsee to form behind the natural dam. Once much larger and deeper, the lake gradually became smaller and shallower as debris washed down from the Totes Gebirge accumulated in its basin. Torrential rains and melting snow in particular can carry enormous quantities of rocky debris into the lake. In the marshy siltation zone where this photograph was taken, the water is now only 50 centimeters (20 inches) deep.
Almsee is often enveloped in dense fog. Cool, moist air flows down from the mountains, which rise only six kilometers (3.7 miles) away. When this cold air encounters the warmer air above the lake, fog begins to form. The effect is especially pronounced in autumn, when clear, cold nights cause the valley to cool rapidly and a layer of cold air accumulates above the relatively warm lake. Dense banks of fog then drift across the water, transforming the appearance of the landscape from one minute to the next. Combined with the vivid colors of the autumn foliage, the first light of dawn creates enchanting, almost fairytale-like moods. When the fog obscures both foreground and background, the marshy siltation zone and the surrounding forest seem to float in space, like a forgotten landscape in which our ancestors once found their home.
