First published: 20/07/24.

Clyde 2.5

Evaporitic Karst And Caves

Evaporitic Karst and Caves (Inscribed)

Evaporitic Karst and Caves by Clyde

I visited this WHS in June 2023. Since I visited before inscription I wasn't sure which components would be inscribed or left out, so to be on the safe side I picked the 200 million year old circa Triassic Gypsums (Gessi Triassici) evaporite karsts around the Alta Valle Secchia component, making sure to visit the Tanone Grande-Tanone Piccolo cave system which is mentioned quite a number of times in the nomination dossier. Not being a speleologist and usually not so comfortable in claustrophobic crawling and messy activities in muddy terrain, my target was to safely get to the entrance of the caves alone and explore a small area which is clearly in the core zone (a headlamp and a hard hat are a must).

Visiting on a sunny summer day, I followed the best stretches of the Sentiero Spallanzani route along the Secchia river streams and stopped at a number of panoramic viewpoints to see the Triassic Gypsums and the Bismantova outcrop of the Reggiano Apennines. Perhaps one of the best panoramic viewpoints, close to the Triassic Gypsums, is known as Ponte della Pianellina where one can gaze at the Monte Rosso, Monte Merlo and Monte Carù slopes together with the U-shaped karst valley, while also cool down in the freezing stream waters. This area is also part of the Parco Nazionale dell'Appennino Tosco-Emiliano and also part of UNESCO's Man and the Biosphere Programme. It is also a Site of Community Importance and a Zone of Special Protection of the Natura 2000 network.

The whitish outcrop of Monte Rosso is very easy to spot, especially after the huge mudslide of Sologno. It consists of Upper Triassic gypsum rocks (216-203 million years old), among the oldest of the Northern Apennines, it is surrounded by younger shale formations and is about 250 metres high. During the Upper Triassic, when the appearance of the continental masses was very different from today, the water of the ancient Tethys Sea deposited gypsum and halite evaporating into wide lagoons. Today the evaporite strata appear strongly deformed and fragmented because they were buried below a thick pile of sediments  and because of the intense strain phenomena related to the collision between the European and African plates. The evaporite rocks are easily deformable and acted as the main detachment horizon along which huge rock masses were thrust into stacks so that one lies on top of the other. This structure developed during the uplift of the Apennine chain.

Halite is more soluble than gypsum and is present intermixed with the gypsum, but nowadays it remains only underground at depth, where it is actively dissolved by the meteoric waters infiltrating the gypsum rocks. This is the reason why the waters of the worth visiting Poiano Springs nearby are salty. Gypsum is soluble in water, and meteoric and stream waters flowing into fractures enlarge them progressively by dissolution. The results are karst features such as bowl-shaped depressions called doline and karst caves: tane and tanoni (lairs), as well as pozzi (shafts or wells). The waters of the Sologno stream, flowing downhill, enter the gypsum hill forming the Tanone Grande della Gaggiolina karst system. For this reason, the streambed section downstream of the sinkhole is commonly dry. The underground waters again reach the surface, forming a resurgence,  a few kilometres downstream and flow into the Secchia River. Towards the left of the Ponte della Pianellina is the Monte Caldina karst system which reaches the record depth of 265 metres and is the deepest gypsum cave in the world.

Towards the right of the Ponte della Pianellina, along the Strada Provinciale Bondolo-Carù (from Castelnovo ne' Monti), follow the hiking signs slightly uphill and head to the right towards S.S.P. Cerro Sologno. After reaching an area full of chestnut trees, I followed my GPS location on my mobile phone and compared it to the accurate spot on Google of the Tanone Grande della Gacciolina cave. The spectacular entrance is almost hidden beneath a doline rockfall now fully surrounded by chestnut trees on top and a variety of ferns and vegetation which usually grow in colder regions, thanks to the particular microclimate around the cave entrance. There are signs warning of frequent rockfalls everywhere and after scrambling on a number of rocks, the first fluttering bats flew towards me in the humid pitch dark cave, and I decided to head back to the entrance and back to safety.

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