Karst Landscapes and Karrenfields The Mediterranean island of…

Karst Landscapes and Karrenfields The Mediterranean island of…

Karst Landscapes and Karrenfields

The Mediterranean island of Mallorca is well known for its spectacular karst features including vast underground cave networks, gorges, and poljes (large depressions) several km wide. But when I took part in a field trip to the island in 2013, the beautifully-eroded slopes in the karrenfields were what amazed me the most. Pictured are rinnenkarren on the sides of the Sa Calobra Gorge, within the Serra de Tramuntana mountain range on the northwestern coast of Mallorca.

Karst landforms are distinctive due to their formation from the dissolution of chemically soluble rocks, such as limestone, by water. When rainwater reacts with carbon dioxide in the atmosphere, it forms carbonic acid. This acid interacts with the limestone causing disassociation of the calcium carbonate into calcium and bicarbonate, effectively breaking down the rock. Limestone dominates Mallorca, comprising over 60% of the island. The majority of this limestone was originally formed on the ocean floor during the Mesozoic, some 65 – 225 million years ago. When the African and Eurasian plates collided around 25 million years ago, this seafloor was uplifted forming the mountain belt.

Karren form due to the dissolution of limestone by rainwater under subaerial conditions. They form straight, parallel solution channels that dip in the direction of the sloping rock face giving outcrops a characteristic ‘furrowed’ appearance. Larger features, known as rinnenkarren, form from the movement of water flowing down the surface of the rock. These channels are often several tens of meters long, and tens of centimeters wide and deep. Rillenkarren are smaller, generally less than a meter long and only a couple of centimeters wide and deep.

The typical Mediterranean climate in the Serra de Tramuntana mountains makes it the perfect place for karren to form. The area has a mean annual temperature of 15°C and gets more than 800 millimeters of rain a year. Karren are best formed at elevations of 200 – 700 meters above sea level, resulting in the large karrenfields which dominate the mountain slopes at these elevations.

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Sources

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Personal Photo.