Nature Reserve Sonnebierg

The Sonnebierg nature reserve is located in the Luxembourg village of Helmsingen, which belongs to the municipality of Walferdingen. The area, covering 15.03 hectares, has been designated as a nature reserve since July 31, 1989.
The Sonnebierg is situated on a slope at the eastern edge of the Alzette valley. Over millennia, this river has carved deep into the Luxembourg sandstone, which dates back to the middle Lias period, exposing the underlying layers. The substrate of Sonnebierg consists of stratigraphically middle Keuper layers. These are mainly composed of colorful marls interspersed with layers of harder light gray dolomite, as well as individual nests of gypsum and calcite. At various locations, layers of massive gypsum can also be found. These formed the economic basis of the now-closed Walferdingen gypsum mine. The resulting soil resembles a dried Sahel steppe in dry conditions, while in the rain, due to its clay components, it acts like a slippery soap. One of the main features of Sonnebierg are the numerous craters and holes that are visible everywhere on the hill. These were formed because the tunnels of the gypsum mine extend through the interior of the Sonnebierg, several of which have since collapsed.

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