Here, at the geological outcrop at Mount Weilberg, we get an idea of how the Siebengebirge came into being. About 30 million years ago, in the Oligocene and into the Miocene, all hell had broken loose.
Volcanic activity in our region
In a first phase of eruption, lava and large quantities of stones came out of the interior of the earth to the surface. Here, they slowly cooled off. These were the trachyte tuffs, covering an area much larger than today’s Siebengebirge.
After that, in a second phase of volcanic eruption, the trachytes came. However, they got stuck in the thick layer of trachyte tuffs and arched it upwards, forming numerous mountains. Drachenfels, Schallenberg, Geisberg, Jungfernhardt, Lohrberg, Perlenhardt, Wasserfall, Großer Ölberg und Lahrberg came into being.
In a third phase of volcanic eruptions, the latite tuffs and latites appeared. They broke through the layer of trachyte tuffs and on their turn formed mountains. These were Wolkenburg, Bolvershan, Hirschberg, Stenzelberg, Lahrberg, Himmerich, Mittelberg and Broderkonsberg.
Finally, a last eruption phase occurred in the Miocene. Now the lava brought basalt and basalt tuffs. The last mountains to appear were Asberg, Leyberg, Scheerkopf, Petersberg, Nonnenstromberg, the core of Großer Ölberg, Kleiner Ölberg, Dollendorfer Hardt, Rabenley Finkenberg.
In millions of years, wind and weather gave the Siebengebirge its present form.
The early geologists doubted
The early geologists, and even the famous Alexander von Humboldt, could not believe that the Siebengebirge was of volcanic origin. Today we know that our region, the Middle Rhine, was part of a continental fault line system. Along these lines continents may break apart, and volcanic eruptions may occur.