IntroductionThe volcanoes of the Siebengebirge arose in the Tertiary Period, 28 to 15 million years ago. The volcanic activity occurred in two phases. First, gas-rich and explosive magmas from the earth crust penetrated to the surface. When they erupted, large amounts of volcanic ash and scoria were ejected, covering the surface in thick layers. During the second phase of volcanic activity, less explosive magma intruded into the previously formed tuff cover. The magmas got stuck just below the surface and cooled down in the form of rounded lava domes or rock passages. Basalt rocks formed, creating sometimes nice basalt columns.
The current shape of the mountains was mainly created in the last 5 million years, when the Rheinish Slate Mountains were increasingly lifted out. As a result, the Rhine cut more deeply into the subsoil and in the process prepared the source crests from their tuff mantle.
See also: Sentinel hub | Landsat 8 | NASA FIRMS