The Glarus Thrust

On the faces above Elm an almost ruled line runs across the rock, with pale grey limestone below it and dark red brown rock above. The upper rock is by far the older of the two: a slab several kilometres thick was pushed many kilometres north over younger material as the Alps formed, and erosion has since cut through it so cleanly that the join can be followed by eye across whole mountainsides. Geologists worked out here how such overthrusts happen, and the area was added to the World Heritage list for it. Above the village the ridge of the Tschingelhörner carries a natural hole, the Martinsloch, through which the sun strikes the church at Elm twice a year.

History

Hans Conrad Escher von der Linth was the first naturalist to notice that here, against the rule that younger rocks lie on older ones, older rocks lie on top of younger, and his son Arnold, the first geology professor at the ETH in Zürich, mapped the structure and thought it might be a huge thrust; in 1848 he showed it to the British geologist Roderick Murchison, who agreed, but in 1866 he published it instead as two overturned folds, an idea he privately admitted was absurd. His successor Albert Heim at first kept the double-fold view, while Marcel Bertrand read the structure as a thrust in 1884, and from 1893 Hans Schardt and Maurice Lugeon found further great thrusts in western Switzerland; the Helvetic nappes are now known to have been pushed more than 100 kilometres north, and the contact shows at Lochsite near Glarus and in the Tschingelhörner cliff with its Martinsloch (Wikipedia, Glarus thrust).

What's there

• The thrust line - a sharp boundary running across the mountain faces above Elm.
• The Tschingelhörner - the serrated ridge carrying the clearest exposure of it.
• The Martinsloch - a natural hole in the ridge, lit through onto Elm in spring and autumn.
• The geology trail - marked routes with boards explaining what the rock is doing.

When to go

June to October, when the high paths are clear and the chairlift runs. The sun passing through the Martinsloch onto the church happens over a few days in spring and again in autumn, at a fixed early hour, and draws a crowd to the village. Clear air after rain shows the colour difference in the rock best.

Things to know

This is a landscape you have to want to read: without a board or a guide the line is easy to miss and looks like a stripe on a hill. Reaching the good viewpoints means proper mountain walking of several hours with real height gain. Elm is small and quiet, transport is limited, and cloud on the faces hides the entire point.

Nearby

Elm and the Sernf valley, with Flims and the Rhine gorge over the passes to the south.

Key facts