Siebengebirge - Geowanderung: Hölle

The Große Hölle, an area between Nachtigallental and Wintermühlenhof, is crossed by a hiking trail that was once used to remove rocks. Today, this path forms a cut up to 20 meters deep in the tuff rock, a so-called Höllentuff, and was probably created by a large fissure in the rock, which was washed out and penetrated deeper and deeper into the rock through use. This tuff layer is up to 100 meters thick in the central Siebengebirge and is a special feature. In the Nachtigallental valley, the tuffs lie directly on the Devonian bedrock, probably close to an earlier ejection point. At that time, the Siebengebirge was covered by thick layers of deposits from various volcanic eruptions that had not yet solidified. During heavy downpours, streams of mud were created which rolled down the slope onto the tertiary sands and gravels. In the process, they picked up further rock fragments from the subsoil. Over time, the mudflows solidified into the Höllentuff, a loose rock that can be seen in the Nachtigallental. This tuff was not commercially exploitable, in contrast to the light-colored, quartz-trachytic normal tuff, such as that found in the Ofenkaulen area, which is finer grained.

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