The basal complex here consists of Lower Devonian clay slate, sandstone and greywacke (Siegen tier / Herdorf layers), almost entirely covered by maar tuffs.
The Pulvermaar is like a picture from storybooks: It is the best preserved maar in the Eifel. The cone is entirely filled with water and surrounded by an almost closed tuff ridge (max. height approx. 45 m). It is also the maar lake with the largest expanse of water and greatest depth in the Eifel and one of the deepest lakes in Germany!
In the tuff pit at the southern inner ridge of the maar cone the tuff ridge layers are 10 m high. Looking from the bottom, the first
8 m consist of an alternating sequence of coarse (especially slate fragments of various sizes) and fine layers (ash). They were deposited
by turbulent ground streams of approx. 200° (glowing clouds) coming from the cone right after the explosion. The upper 2 m consist of fine, even layers of ash which later rained out from the air. To the south, directly at the bank path, one can see a basaltic path in the ridge. It probably pushed through coming from the Römerberg, through the maar tephra (pyroclastic deposits).
What actually is a maar?
The term Maar is derived from the Latin "mare" (=sea). It is a type of funnel-shaped volcano formed by eruptions of water vapour, which is "blasted" into the landscape and often presents itself as a bowl-like shape. A maar is formed when rising magma meets water-bearing rock layers. Violent explosions occur and the surrounding rock is shredded together with the magma into its smallest components and thrown out of the explosion funnel. A cavity forms in the area of the explosion hearth, which merges into an explosion vent. As the rock above the cavity collapses, the explosion vent becomes a collapse or maar funnel. After the volcanic activity subsided, the funnels subsequently filled with water. A total of over 70 maar volcanoes have been counted in the Eifel, twelve maars are still filled with water today, the rest have already silted up.