9. The Ground Failure Moraine Muskau Arch (Muskauer Faltenbogen): A Special Kind of a Glaciotectonic Composite Ridge

The Muskau Arch is a beautifully formed, horseshoe-shaped glaciotectonic composite ridge formed by an inland ice glacier. Geographically, it is a spatially and structurally distinct part of the main ice margin of the Saalian Warthe period. However, it was formed in the early Elsterian Ice Age. Due to a special surface morphology in the form of small valleys without drainage, the so-called Gieser, as well as very extensive geological investigations for the raw materials, especially lignite, it is geologically the best documented and researched composite ridge worldwide. By balanced geological sections, it was possible to show that its formation cannot be attributed solely to a horizontal compression, which is classically assumed, but is the result of a two-stage formation process. In a first deformation step, the advancing, deforming Muskau glacier lobe caused ground failure in its unfrozen, loose sedimentary bedrock. In the second step, the glacier pushes and overthrusts the composite ridge, starting from the terrain depression caused by the ground failure. According to this genetic model, the Muskau Arch is referred to as a ground failure moraine. The geomorphological and structural geological classification of the Muskau Arch in relation to the surrounding Pleistocene glacial landscape is presented. Furthermore, the Muskau Arch is described in detail as a medium-size landscape element (landform) with its most important geosites. The Muskau Arch UNESCO Global Geopark was established in the territory presented in this chapter, showcasing the landscape of glacial origin as well as historical industrial development use of raw materials, mainly lignite. Today, the Muskau Arch is an attractive natural, cultural and post-mining landscape, with adequate tourist infrastructure.