The sky in the Brohl valley darkened as the Laacher See volcano erupted just five kilometers away. A red-hot mixture of lava particles and gases shot up into the atmosphere at intervals. Each time the eruptive column collapsed, the material rushed through the surrounding valleys as if on a cushion of air - ash and lava particles filled the valleys up to 60 meters high. Over the course of time, the once loose material from the pyroclastic flow has caked into a rock that is called “trass” in our region.
The Romans already mined trass in the Brohl valley and used it to build houses, among other things. When finely ground and mixed with lime and water, it produces a mortar that also hardens under water. It is likely that it was the Dutch who pushed mining in the Brohl Valley from the 16th century onwards, as trass is ideal for building dykes and harbors.
They were also the ones who gave the volcanic cement its name: “Tyrass” is Dutch and means “glue”. The trass walls you see from here have been hollowed out by quarrying and can be visited.
Due to their poorer quality, they were no longer of interest for mining and are now an impressive testimony to the huge pyroclastic flow that once filled the entire valley.
