Engineering Geological Map of Lower Saxony 1: 50 000 — Salt Stockings

Subrosion is the underground leaching and transporting of mostly easily soluble rocks. Subrodable are chemical sediments, such as the easily soluble chlorides stone salt and potassium salt, sulphate rocks such as plaster and anhydrite (sulfate carbonate) and the heavier soluble carbonate rocks e.g. limestone (carbonate carbonate). Most of the damage in Lower Saxony is due to the leaching of sulphate rocks. In subrosion, it is necessary to distinguish between regular and irregular leaching. Regular leaching takes place extensively on the surface of the subrodable rock and leads to wide, usually small reductions of the terrain. Irregular leaching focuses on a small-scale, narrowly limited area and can lead to the formation of caves, muds or gutters. It progresses in the solid rock mainly along crevices or joints in the rock. Therefore, loosened mountain areas in tectonic disturbance zones are also mostly areas of intense subrosion. If the boundary load capacity of the mountain above a cavity is exceeded, this cavity can collapse and break through to the earth’s surface (earthfall). The layer strength of the soluble rock and thus the possible size of a cavity are decisive for the size of the burglary on the terrain surface. About 50 percent of the earthquakes in Lower Saxony have a diameter of up to two meters and about 40 percent the diameter is between two and five meters. Although these diameters appear quite small, the impact on structures can be very large. On the ISH50 map, on the basis of the Geotectonic Atlas of Northwest Germany, 1:100,000 saltstock highlands were identified, in which salt rocks occur above -200 m NN — in a few exceptions above -300 m NN — and are surrounded by groundwater layers. Here, by leaching in the area of the salt level, surface reductions and leaching in the area of the gypsum hat can occur. The information shown in the map does not replace a ground study according to DIN EN 1997-2 (DIN 4020).