Geology and formation

Stone runs form when a layer of clay in the soil prevents lime-rich groundwater from seeping downward. If this spring water then flows very slowly over a gentle slope, the lime dissolved in the water reacts with the oxygen in the air and is deposited as solid limestone. This mostly happens along the edges of the stream, so that over time a raised channel forms, with a central groove where the water continues to flow.

Stone runs are a unique feature of lime-rich regions such as the Rohrbach Valley. In Germany, they mainly occur in the karst landscapes of the Franconian Jura and the northern edge of the Alps. They are especially found in deciduous forests with nutrient-poor soils.

Only six such stone runs are registered in Bavaria as geological natural monuments, four of them in the district of Weißenburg-Gunzenhausen.

The Stone Run at Rohrbach is about 80 meters long and 1–2 meters high.

Growth Rate: A few millimeters to two centimeters per year.

Vulnerability: Their growth can be interrupted by falling leaves, so most stone runs rely on human maintenance to survive.

Adaptable and Full of Life

Such special habitats are home to rare species like: Bechstein’s Bat Roosts in humid places and hunts insects in richly structured forests. Purple Emperor Butterfly Strongly dependent on specific plants like aspen and goat willow. Broomrape A parasitic plant that taps into the roots of others to feed. Bistort A moisture-loving plant with prominent flower spikes. Lesser Stag Beetle A beetle whose larvae develop in dead wood; prefers old broadleaf forests. Alpine Dock Found in moist meadows and forest clearings; rare in Central Europe. Black Woodpecker The largest native woodpecker; carves large nesting cavities in old trees.

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