English: Cross section of the Urach-Kirchheimer Vulkangebiet (german wikipedia), Swabian Alb. Most of the many volcanoes were of the Phreatomagmatic eruption type. The very small “Scharnhausen Volcano”, only 9km south of Stuttgart, is of prominent geological importance, as non-volcanic fragments of Upper Jurassic (Malm beta) were found within the rest of the diatreme. However, at the volcano’s location all strata of the South German Jurassic (Upper-, Middle- and Lower Jurassic) have meanwhile totally eroded away, yet during the volcanoes activity in Miocene were still cropping out.
While most of the volcanic pipes below the Swabian Alb eroded little and formed depressions, those of the foreland eroded heavily, morphologically hiding or forming conical hills.