Siebengebirge - Geo Hike: Hell

The large "Hölle", an area between Nightingale Valley and Winter Mill Court, is intersected by a hiking trail that used to be used for transporting rocks. Today, this trail forms a cut up to 20 meters deep into the tuff rock, a so-called "Hell Tuff", and probably originated from a larger fissure in the rock that was eroded and deepened through use into the rock. This layer of tuff has a thickness of up to 100 meters in the central Siebengebirge and is a unique feature. In Nightingale Valley, the tuffs are stored, probably near a former vent, directly on the Devonian bedrock. At that time, the Siebengebirge was covered by thick, still poorly consolidated layers of deposits from various volcanic eruptions. Heavy rainstorms created mudflows that rolled downhill onto the tertiary sands and gravels, picking up additional rocks from the subsurface. Over time, the mudflows solidified into Hell Tuff, a loose rock that can be seen in Nightingale Valley. This tuff was not commercially usable, unlike the light, quartz trachytic Normal Tuff, such as that found in the area of the Oven Caves, which is finer-grained.