Swabian Jura - Geology

Geology

The geology of the Swabian Jura is mostly limestone, which formed the seabed during the Jurassic period. The sea receded 50 million years ago. Three layers of different limestones are stacked over each other to form the range: black jura, brown jura, and white jura. White jura may be as pure as 99% calcium carbonate. Since limestone is soluble in water, rain seeps through cracks everywhere and forms subterranean rivers which flow through a large system of caves until they emerge. Thus there are hardly any rivers, lakes or other forms of surface water on the plateau.

In some places, former volcanic activity has left traces, such as maars and hills. In the west, the Zollerngraben (a geological depression in a tectonically active region) sometimes causes mild earthquakes. The Nördlinger Ries is a large meteorite crater (15 million years old).

Tertiary relicts can be found at the southern part of Swabian Jura. Famous locations are known of Ulm area (e.g., Turritellenplatte of Ermingen).

Constant rain and other weather influences are slowly dissolving the entire range. Each year, it loses approximately 5 cm (2.0 in). Some millions of years ago, the mountains reached as far as Stuttgart. In some places, the limestone was more resistant to decay and thus the recession of the main range has left small mountains (called "Zeugenberge" — "witness mountains"; e.g. the Achalm or the Hohenstaufen) which testify to the former territory of the range. The omnipresent caves are great tourist spots, beautiful and not very crowded. Many different types can be found, from dry dripstone caves to caves that can only be entered by boat. Sometimes the discharge of the water from subterranean rivers can be spectacular, too, e.g. the Blautopf, a source for a tributary of the Danube. Also because of the porous limestone, the Danube nearly disappears near Immendingen (in 1911, 1921, 1928 and 1943 it disappeared completely), only to reappear several kilometers further down. Most of the water lost by the Danube resurfaces in the Aachtopf, a spring for a tributary to the Rhine.

The soil is not very fertile, the humus is often as thin as 10 cm (3.9 in). Many small limestone pebbles are found on the surface.