Riedener-Vulkankomplex - Geopfad-Route R

Alongside the Wehrer Kessel and the Laacher See, the Riedener Kessel is one of the three large "pumice volcanoes" in this region, which volcanologists call the "volcanic field of the Eastern Eifel". There were also at least three eruptions from the Kempenich basin, but most of them were of a phreatomagmatic nature. The magma had a foiditic composition and was very similar to the magma of the Herchenberg volcano in its lack of silicon.

The Laacher See volcano erupted once around 13,000 years ago, the Wehrer volcano erupted three times around 200,000 - 100,000 years ago and the more recent two of at least three eruptions of the volcano located in the Kempenich basin took place around 425,000 years ago (see time table in the hiking guide, page 11). The Rieden volcano was active around 440,000 - 390,000 years ago and experienced eight major and at least six minor eruptions during this time. The major eruptions came from five different craters located in the immediate vicinity of the village of Rieden and at the south-western foot of the Hohe Lei.

Before we start, we need to know that tephra refers to all particles of any size that are ejected during a volcanic eruption. Tuff (called tufa by the stone industry), on the other hand, is ash solidified into stone. Ash, on the other hand, is not something that has been burnt, but refers to all particles up to 2 mm in size that are ejected from a volcano. In particular, these are microscopically small glass fragments that are produced during volcanic explosions when the molten rock, the magma, at a temperature of around 700-1100 °C is torn apart.

Ash particles are therefore mainly small fragments of pumice, which is nothing more than highly porous magma solidified into glass.

The rocks of the Rieden tuffs are known as leucite phonolites because, unlike the phonolites of Lake Laach, they do not contain plagioclase.They do not contain plagioclase, which is a tabular calcium-sodium-aluminum silicate belonging to the feldspar group.

The magmas were so poor in silicon that the feldspar plagioclase, which otherwise occurs as a main component, could not grow in the magma. Instead, so-called feldspar representatives such as nepheline (sodium aluminum silicate) and - due to the high potassium content of the magma - leucite (potassium aluminum silicate) grew. As the Rieden magma was also very rich in sulphur, the mineral nosean, a sulphur-containing sodium aluminum silicate, the calcium-poor brother of haüyn, which is common at Lake Laach, often grew in addition to nepheline.

The rocks of the volcanic cones around the Rieden tuffs and those of the Rieden maar eruptions should therefore not be referred to as "basalts" - although they can hardly be distinguished from them visually, as they do not contain plagioclase. Because they are low in silicon and rich in potassium, they are called leucitites and are rarities on all continents, e.g. in the Leucite Hills, USA, in the Virunga Mountains of East Africa, at Gaussberg, Antarctica, or in the Alban Hills and Vesuvius, Italy.

The abundance of a black, often centimeter-sized mica (potassium-magnesium-iron-aluminum silicate with crystal water), which is not called biotite but phlogopite because of its magnesium content, is also striking.

You can also find a detailed description with background information on the website of our volcano park guide Konrad Friedgen:https://profirouten.de/eifel/geopfad-route-r-riedener-vulkankomplex