The maar is located precisely at a SE-NW disruption in the basal complex. To the southwest, Lower Devonian grey-green sand and siltstone – some quartzitic – of the Reudelsterz layers crop out, to the northeast is the Lower Devonian, structureless Ulmen tier with sand-, siltstone and clay slate. Maar tuffs cover the Lower Devonian. Particularities At about 10,900 years, the Ulmen maar is the latest volcanic eruption in the Eifel and also in Germany. The eruption occurred during a warm period of the late- or post-glacial period, since plant remains were found at the base of the Ulmen maar ashes. The ash field can now still be detected at the surface up to 600 m southwest. The thickness of the ash ranges from 15 m directly at the edge of the crater (almost complete tuff ridge) up to 0.2 mm at the Meerfeld maar about 20 km away. Since 1926 the waterworks for the Cochem-Zell district has been obtaining drinking water from the 39 m deep maar lake with the help of 8 wells. A population of 30,000 benefit from the 700,000 m3 of drinking water produced annually.