Living with Supervolcanoes in Saxony: The Fossil Lake Börtewitz

The Rochlitz Caldera: Tracing Prehistoric Volcanism

Supervolcanoes in Saxony: Around 290 million years ago, the Permian period brought intense volcanism to Saxony. This violent activity occurred in the region between Rochlitz, Grimma, and Mügeln. As a result, the eruptions left behind a massive collapse depression. This area is known today as the Rochlitz caldera. Furthermore, it spans a diameter of more than 30 kilometers.

Today, the caldera is filled with various types of porphyry. These rocks are all direct products of ancient volcanic activity. However, the rock layers near Börtewitz hide a special secret. They have preserved the rare remains of plants and animals. Therefore, we can experience the living world between the volcanoes.

Over millions of years, the porphyry weathered to kaolin on the surface. This valuable porcelain clay is still mined today between Kemmlitz and Mügeln. In addition, inland glaciers moved across the region several times during the Ice Age. Consequently, these glaciers exposed the hidden porphyry and lake deposits for us to discover.

The Fossil Lake of Börtewitz: A Discovery of International Importance

The fossilized remains of an ancient lake recently came to light in an open pit. This unique lake existed 290 million years ago. Since 1989, scientists have conducted several geoscientific excavations here. For instance, the Freiberg University of Mining and Technology led these efforts alongside the Schleusingen Natural History Museum. Consequently, the teams discovered incredibly rich fossil material.

The fossil-bearing layer is almost ten meters thick. It consists mainly of yellowish to light-brown mudstones. These stones are hard, finely layered slabs of silicified lake deposits and volcanic ash. Furthermore, they contain spectacular remains of conifers and fern seeds. You can also find amphibians, fish, arthropods, and insects here.

Unfortunately, violent ash eruptions extinguished Lake Börtewitz several times. However, the lake always re-formed during dormant periods. This cycle continued over the course of more than 4,000 years. As a result, the unique habitat repeatedly attracted new populations of amphibians and fish.

Permian Ecosystem Research: A Window into the Past

Paleontologists recovered unique fossils in Börtewitz. These finds provide vital information on Permian ecosystems under changing environmental conditions. In addition, these discoveries are of international importance. They perfectly complement other fossil finds in Thuringia and the Chemnitz area. Therefore, scientists use them to reconstruct prehistoric life on a global scale.

These fossils are clear evidence of a highly specialized habitat. The ecosystem featured a relatively low species diversity. Nevertheless, it often boasted very high numbers of individual organisms. In conclusion, Lake Börtewitz is an outstanding example of a Permian biotope. It is just as significant as the famous petrified forest excavated in Chemnitz.

Image Captions (Short & Punchy)

  • The exhibition “Supervolcanoes in Saxony” is located in the Röcknitz Geoportal. It displays the volcanism and the living world of 290 million years ago.

  • The Rochlitz eruptions produced kilometer-high ejections of ash and gas. For example, this process is similar to the modern Bromo volcano on Java. These heavy ash falls repeatedly buried Lake Börtewitz.

  • You can visit two main theme rooms in Röcknitz. These are the “Supervolcanoes” room (above) and the “Biosphere” room (below).

  • This graphic shows the bedding conditions of the rock layers. It also shows the age of the Börtewitz fossil lake geotope.

  • The first excavation in 1989 required pure muscle power. Later, the team received technical support from Kemmlitzer Kaolinwerke GmbH. The man in the pale orange T-shirt is Dr. Harald Walter. He is the original discoverer of the fossil lake.

  • This section displays the rock profile of the fossil lake. You can see the excavated plants and animals here. Please also refer to the back panel.

  • A dramatic scene unfolds during a volcanic eruption. A freshwater shark hunts its prey, including bony fish and amphibians. Meanwhile, a prehistoric cockroach buzzes curiously above them.

  • A violent volcano buried this ancient forest 291 million years ago. Today, scientists excavate it in Chemnitz. The area contains cordaite, pasronite, and calamite trees. Furthermore, it hides snails, scorpions, and giant centipedes.

Imprint & Credits

  • Concept & Texts: Created in cooperation with the Museum für Naturkunde Chemnitz and TU Bergakademie Freiberg.

  • Photos: M. Bertuch, R. Roscoe, L. Richter, TU Bergakademie Freiberg.

  • Geological Profiles: GEOmontan GmbH Freiberg according to GK50 1992, P. Tschernay 2004, and Schneider & Puschmann 2024.

  • Reconstructions: Museum für Naturkunde Chemnitz based on designs by J. Schneider / F. Spindler and S. Schießl / I. Kogan.

  • Design: Lars Hoschkara, DESIGN & MULTIMEDIA (Wermsdorf). ((Supervolcanoes in Saxony))