The path taken by the water from the drainage catchment area to the area where the Höllgrotten caves were formed.
The Höllgrotten caves are unlike any other dripstone cave in the world. While other grottos were carved from solid rock by underground watercourses in a process lasting millions of years, the Höllgrotten caves were formed on the surface over a comparatively short period of about 3,000 years, making them relatively “young”.
BRING DOWN THE CURTAIN!
The calcareous (rich in calcium carbonate) water rising here after the end of the last Ice Age created a spring tufa formation in which the Höllgrotten caves were formed.
The Lorze ravine was formed by glacial meltwater released from the Ägeri valley when the last Ice Age came to a close about 18,000 years ago. Having drained into the Neugrund moors in Menzingen, 4.5 km (2¾ miles) above the cave site, the water leached large amounts of calcium carbonate from the surrounding rock in the course of its ten-year underground journey before rising in great springs from the flanks of the Tobel at the spot where the Höllgrotten caves now stand. As the emerging calcareous springwater ran off on the surface it deposited large volumes of calcium carbonate around the mountainside, forming in the period between 8,500 and 5,500 years ago a gigantic mass of spring tufa about 30m (100ft) high, 50m (165ft) deep and 200m (660ft) long.
Where strongly calcareous springwater rises to the surface, clumps of moss, ferns, twigs, leaves and sand calcify to form spring tufa, a so-called speleothem or secondary mineral.
The mass of tufa continued to expand along the bed of the Lorze, causing the stream to flow underneath its leading edge and form niche-like hollows and overhanging ledges. A void was created by falling rocks when the formation collapsed at a point close to the modern-day cave exit and the remainder of the caves were then slowly enclosed: curtains of roots and moss propagated by the emerging springwater quickly grew and calcified, forming dripstone caves in the spaces created behind the screen of tufa.
DISCOVERED THANKS TO THE RAILWAYS
The old quarry
Light, porous and easy to cut, the tufa deposited in the Lorze ravine was quarried in the 19th century for construction projects such as the cladding for the Bonstetten railway tunnel in Knonaueramt. Access to the first grotto, which had been discovered in the course of quarrying in 1863, was hampered by the presence of underground lakes. Tufa quarrying was fortunately halted in 1885 to preserve the grottos and in the same year, Ständerat (Councillor) Josef Leonz Schmid, whose father had discovered the caverns, ordered the construction of an adit (a type of mineshaft) to drain the cave lakes into the Lorze. The Höllgrotten caves have been open to the public since 1887 and further sections of the grottos were discovered in 1892 and 1902. Ständerat Schmid purchased neighbouring plots of land to ensure he would be able to link up all the grottos and preserve the cave system for posterity.
The first tourists to be enchanted by the caves arrived in 1887, as depicted in this contemporary illustration.
In 1917, a man-made shaft was excavated to link the lower caves with the upper grottos, 40m (130ft) above, and it is now possible to walk through the entire Höllgrotten cave system from beginning to end.
Since spring 2012, the grottos have been illuminated with cutting-edge LED technology, affording the very first opportunity for visitors to enjoy a proper view of the stone’s vast range of shapes and colours in all their subtlety.