Over the past 2.6 million years, there have been about 50 glacial periods in Central Europe. We use the term glacial period when the annual mean temperature is significantly below 0 °C for several thousand or tens of thousands of years. These glacial periods are separated by interglacial periods with mean annual temperatures of 8 °C or above.
Only the last three glacial periods were also partial ice ages in our region. The term ice age means that more snow falls during the winter than melts in the summer. The result is the formation of an inland ice mass that spreads southward from Scandinavia into areas of northern Central Europe.
During the Elster glacial period, northern Central Europe was covered by inland ice two times. At the beginning of the second glacial advance, about 340,000 years ago, the ice margin stretched across Europe along the Hamburg – Berlin – Warsaw line for more than 1000 km. During its continued southward advance, a glacier tongue approximately 20×20 km in size – the Muskau Glacier – broke away from the inland ice mass and moved southward more rapidly than the entire ice front. Geotechnical modeling has determined its thickness to have been between 400 m to 500 m. Compared to today’s mountain glaciers, the Muskau Glacier was distinctly short and thick, but relatively wide.
The Situation before Glaciation
In a relatively flat landscape, a “small” glacier tongue formed. It is not known why the glacier broke away at this particular location. Perhaps the valley of a small river or stream existed here, which facilitated the outflow of the ice. Such a river and its valley, however, have nothing to do with today’s Neisse River, which was formed much later.
The Muskau Glacier in Action
The layers under the ice were folded by rock flow (plastic deformation). This can be imagined as if the subsurface was clamped between the jaws of a vice. One “jaw” is the Earth, which “holds firm” from below. The second “jaw” is the ice pressing down from above. In front of the ice, rupture deformation predominantly took place. Here, the layers fractured into so-called tectonic flakes. These were uplifted and compressed into a 130 m to 180 m high, and about 700 m wide, pushed end moraine.
The Muskau Arch was therefore not “pushed together” by the shear force of the glacier, but rather “crushed” by the weight of the ice (ice load deformation). In architectural engineering, the deformation of the subsoil by the load of a building is called “ground heave”. That’s why the Muskau Arch can also be referred to as a ground heave moraine.
After the Melting of the Glacier
After the ice melted, the folding and fracturing processes in the land behind the moraine created a basin (Bahren Basin), which gradually filled up with varved clay. Varved clays are sedimentary layers deposited by meltwater in a lake. Today, the Muskau Arch and its filled-up interior is the largest contiguous woodland area in Brandenburg.
Subsequent glacial advances during the Elster and Saale ice ages swept over Muskau Arch, and glacial winds blew off fine sediments (sands, silts and clays). Both processes led to a strong leveling-out of the pushed end moraine. During the Weichselian ice age, the ice no longer reached to the area. Today, Muskau Arch only rises a few meters above its foreland – about 10 m on average. The highest level of the terrain is at its inner edge in Poland.