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31.10.2022 - The Tectonic Arena Sardona is a unique illustration of the formation of mountain ranges. It has kept numerous geologists busy over the past 200 years. However, it is also a constantly evolving visitor magnet. And above all, the Tectonic Arena Sardona forms the magnificent backdrop for the fifth stage of the Swiss O Week 2023.

Since 2008, the mountain range between the Walensee(lake), the main valley of Glarus and the Chur Rhine valley has been on the hit list of the UNESCO natural heritage sites. Although, at first glance, it is a mountain range like many others – or is it not? The Tectonic Arena Sardona convinced UNESCO with a strong argument: the so-called Glarner overthrust. It arose from a continental collision between Africa and Europe. It was a collision that did not happen in fractions of a second, but at a snail’s pace. It lasted over millions of years and did not happen on the surface of the earth but at a depth of 15 kilometres. Older Verrucona rocks overlaid much younger Flysch rocks over around 40 kilometres. Limestone, the Lochsite limestone, formed as a kind of “lubricant”.

The "magic line"

There are a number such collision mountains around the world. The particularity about the Glarner Overthrust is that it is immediately recognizable, even for lay-people, because the rocks below and above the overthrust are very different both in colour and in their type of weathering. The razor-sharp boundary, the so-called “magic line”, is immediately noticeable. In addition, the thrust was lifted into an arched position and is visible three dimensionally around the Piz Sardona. The ceiling tectonic can be admired as if in an arena. Hence the wording of the World Heritage Site. Nowhere in the world can this phenomenon be observed as well as in the area of the fifth SOW stage. And nowhere else in the world can one see the results of these processes that lead to the mountain building as clearly and monumentally as here.

The hole in the rock

A special feature in the Tectonic Arena is the Martinsloch (hole). It was created by the crossing of a soft, flat marl layer and a steep upright fracture surface. This allowed erosion to remove limestone more quickly. The breakthrough has the form of a triangle of more than 15 meters width and around 22 meters height and is located below the “Tschingelhörner” mountain ridge. In mid-March and early October, the sun’s rays shine through the Martinsloch onto the church of Elm.

Over 200 years research

It is not surprising that geologists and amateurs from all over the world have been conducting research in the Tectonic Arena for over 200 years. In 1809, Hans Conrad Escher von der Linth (1767-1823) stated that older rocks would probably lie on younger ones. His son Arnold Escher (1795-1883) also devoted extensive studies to the phenomenon. In 1841, he concluded that a “colossal overthrust” was present. However, he shied away from publication of his theory. “No man would believe it and would think me being a fool”, he stated. The geologist Albert Heim (1849-1937) stuck to Alfred Escher’s theory that the phenomenon could only be explained by a single, large thrust. Even today, numerous geologists are continuing to research the main thrust. Their questions revolve around the mechanisms of these powerful processes of mountain building and the types of deformation that played a role.

Discover the Tectonic Arena

The Tectonic Arena is not only a geological marvel, but also a true natural paradise with protected areas for animals and plants. The different altitudes, climatic conditions and the geological subsoil result in a wide variety of habitats. A stop at the visitor pavilion of the Segnes hut is also worthwhile. But none of this should stop the participants of the fifth stage from first focussing on the map and compass on the way to the tectonic arena. The overview of all SOW stages can be found here.

Foto: Philipp Ruggli

Foto: Philipp Ruggli

©Flims Laax Falera
Foto: Rémy Steinegger

Foto: Rémy Steinegger

LK Martinsloch

LK Martinsloch

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