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Karst phenomena: dolines, swallow holes and caves

The soluble nature of gypsum has resulted in karst phenomena developing in extensive areas of the park, creating unique landscapes that are significantly different from those in the adjacent hills. On the surface, there are closed depressions, such as blind valleys and dolines, and the openings to numerous caves, which lead to a complex underground environment. The underground hydrological system is continuously replenished by various sources of water absorption, such as swallow holes, but even through small fractures, resulting in impressive speleogenetic events. Blind valleys form where the gypsum outcropping begins. A small valley lying over an impermeable substrate (generally marl) terminates against gypsum cliffs and the water course disappears underground through a swallow hole, resulting in an authentic subterranean stream. Instead, dolines form above the vast gypsum areas and there are different ways in which they develop. Under various aspects, the park's karst area is of international importance. The Spipola Doline is the largest doline over gypsum across western Europe. The underground cave system, running from the blind valley at Acquafredda to the Siberia resurgence, has an explored length of over 9 km. Gypsum karst has been observed and studied since the 1700s, when the abbot Calindri provided a fascinating description of the Acquafredda valley, however it was Luigi Fantini who began carrying out systematic speleological explorations in the 1930s, resulting in the discovery of numerous caves, including Spipola, and the creation of the Bolognese Speleological Group. Many of the park's caves, featuring formations, concretions and archaeological remains of great scientific importance, are protected and closed to prevent vandalism.