Glarus main thrust fault

History

Just beneath the ridge of the Tschingelhörner, at an altitude of 2,600 metres, the famous Martinsloch opens up. This strange, almost triangular opening, with a diameter of around 18 metres, was formed by the accelerated erosion of a more fragile part of the rock. It is very special since it is a kind of natural calendar. Twice a year, roughly a week before the spring equinox and a week after the autumn equinox, the rising sun shines through the hole and lights up the church tower of the village of Elm, for about 2 minutes. Then it disappears behind the wall of rock before emerging above the ridge some 15 minutes later. This occurrence has fascinated people for centuries. The other mysterious characteristic of the Tschingelhörner and of the surrounding peaks is a grey-yellowish line, wedged between two layers of Alpine rock. This distinct line has intrigues the scientific world for a long time and prompted a considerable number of arguments amongst geologists, since it overturned, in the literal sense of the word, the prevailing theories regarding the development of the Earth’s crust. This “magic line”, as it is often called, ultimately provided a key to our understanding of the tectonic processes that gave rise to the Alps and to other similar mountain ranges.