Approximately 230,000 years after the onset of lake
sedimentation (24.56±0.04 Ma; Mertz et al. 2007), a
basaltic lava flow, originating south of Stöffel hill, filled
the lake in one go, which at that time still had a depth of
several tens of metres (Pirrung 1997). The heated zone was
only 30 cm thick (Radtke and Wuttke 1995). The lake was
Palaeobio Palaeoenv (2010) 90:21–27 23
completely filled, and no younger lake sediments developed.
The basaltic flow preserved the lake sediments, protecting
them in particular against deep erosion after the quaternary
uplift of the Rhenish Slate Mountains.