Explosive volcanism of the West eifel volcanic field, Germany

Abstract

Abstract The Quarternary volcanic field of the West Eifel is located on the Rhenish Massif which is presently rising above an anomalous mantle structure. Magmas of nephelinitic, leucititic, basanitic, tephritic, and phonolitic composition reached the surface in about 240 volcanoes. About 60 maars occur in this classic maar region and the remaining 180 volcanoes are mostly scoria cones. Nearly all maars formed in valleys where abundant groundwater was able to circulate through zones of structural weakness in bedrock beneath the valley floors. The rising magma generally had access to this ground water during the entire period of phreatomagmatic maar eruptions. In contrast most of the scoria cones erupted within small maars (initial maars), which suggests that the magma rising underneath these volcanoes must have contacted only limited amounts of groundwater circulating along hydraulically less active zones of structural weakness. The available water was shut off when the initial maar collapsed and then the magma could rise, intrude the diatreme, and erupt on the maar floor forming a scoria cone in a second eruptive phase. The hydrogeological situation in the Eifel is characterized by zones of structural weakness that exhibit different or no hydraulic activity and it clearly controls formation of the various West Eifel colcano types (maars, scoria cones with initial maars, and scoria cones).