The Mulde – a River through Earth’s History
Background: Supervolcanoes on the Supercontinent
About 290 million years ago, during the Permian period, Saxony was located near the equator on the supercontinent Pangaea. Intense volcanic activity in the region between Rochlitz and Grimma today, resulted in a collapse basin (the Rochlitz Caldera) more than 30 km in diameter. These eruptions also produced the porphyry rocks between Colditz and Kössern, which were later exposed by the Mulde.
- Caption 1: The Rochlitz Caldera, showing volcanic deposits and the current level of erosion
- Caption 2: Rochlitz porphyry from Sermuth; a so-called “fusion tuff,” formed from a mixture of volcanic gas, ash, and magma fragments
Prologue: The Mulde River in the Tertiary Period
During the Tertiary Period (Miocene “Lignite Era”), the coastline of what is now the North Sea lay far south of Leipzig. As early as about 35 million years ago, rivers originating in what is now Bohemia (CZ)—including a “primeval Mulde”—flowed into this primeval North Sea. The slow uplift of the Ore Mountains (Erzgebirge) later blocked the northward course of these Bohemian rivers.
- Caption 3: Scheibenberg (Ore Mountains) 1930: Extraction of gravelly sands from a Tertiary river that flowed from Bohemia toward the “Primeval North Sea,” covered by Tertiary lava (basalt)
The Final Touch: The Mulde and the Inland Ice Sheet
For about 350,000 years, during the Pleistocene (Ice Age), an inland ice sheet from Scandinavia repeatedly advanced across the Central German region, exposing the Permian porphyry rocks once again. As cold and warm periods alternated, the glaciers came to a standstill, advanced, or retreated several times. This process created gravel barriers (moraines). The rivers flowing toward the North Sea had to bypass these obstacles: The Mulde River turned north-west at the ice front toward what is now Naunhof. It was not until about 130,000 years ago that it broke through the moraines and has since flowed northward toward the Elbe.
- Caption 4: Basin evolution since the Miocene and the Ice Ages
Glacial River Terraces: The Geological History of the Mulde River
A wide variety of glacial deposits can be found along the Mulde Valley between Rochlitz and Eilenburg: coarse river-transported sand and gravel, fine material from the glaciers (glacial marl and loam, banded clay), and wind-blown dust (loess). During the most recent warm period (“post-glacial period,” Holocene), the Mulde formed river loops (meanders) with slip-off slopes and cut banks. During floods, the fine material transported by the water was deposited in the lowlands as floodplain clay.
Geologists can reconstruct the shifting course of the Mulde over the past 500,000 years based on valley elevations and the varying gravel composition of the gravel terraces, and from this derive a spatiotemporal model of the entire Mulde river system.
- Caption 5: Geological cross-section through the river terraces of varying ages along the Mulde River near Grimma
- Caption 6: Boulders in the river gravel of the United Mulde provide information about the river’s history
- Caption 7: River terraces and the course of the Mulde River in the Rochlitz/Grimma/Naunhof area over the past 500,000 years
Legal Notice
Concept and text: National Geopark Porphyry Land in collaboration with the City of Colditz;
Photos: Marion Geissler, Frank W. Junge, Max Nowak/Deutsche Fotothek Dresden;
Geological cross-section / maps: Frank W. Junge based on templates by Lothar Eissmann (1975); Block diagram: GEOmontan GmbH Freiberg / Geopark Porphyry Land;
Design: