The west Eifel volcanic field
- Figure Wartgesberg
- Figure Holocene Maar Lake
The West Eifel Volcanic field has more than 250 volcanic structures, most of which are basanitic scoria cones that reach 100 m height with a basal diameter of 600 m. 68 structures are from phreatomagmatic explosions at subsurface depth, which caused deep crater that collapsed and were finally filled with ground water, the so called maar lakes. These lake basins serve as traps for sediment and were filled on average with 1 mm of sediment per year. Accordingly, a 100 m lake fills up within 100,000 years on average, and becomes dry land. Fallout from eruptions near the maar site lead to deposits of decimeter or even meter thickness in the lake sediments. More distant eruptions cause ash layers of several cm thickness. These features are usually directly visible in the cored sediments and can be sampled. We have sampled all visible tephra in all ELSA cores and observed a distinct mineral composition, which can be used as fingerprint to differentiate individual eruptions, see “Tephra” below (Förster & Sirocko, 2016, Förster et al., 2020). The tephra layers are dated with the ELSA-20 age model.
Air photograph of the quarry at the Wartgesberg volcanic complex
The lake sediments thus provide a precise chronology for all eruptions in the Eifel during the lake phase. The resultant ELSA-20 chronology of eruption times has a precision of 150 years relative to the Greenland ice core chronology. In particular, the relative position to warming and cooling events can be precisely determined. Accordingly, most eruptions in the Eifel have occurred in the early phase of climatic transitions from cold to warm, i.e. those times of the geological past, when the load of the continental ice sheets started to lower, whereas global sea level increased.
