From Wikipedia - the subsidence
Since 2008, the centre of the city has reported to have risen some 12 cm, after initially sinking a few millimeters. This has caused considerable damage to buildings in the city centre, including the historical town hall. One hypothesis for the cause of this geological change is a drilling operation conducted in the spring of 2007 to provide geothermal heating to the city hall. The drilling perforated an anhydrite layer and caused high-pressure groundwater to come into contact with the anhydrite, which then began to expand. Currently no end to the rising process is in sight. By 2010 some sections of town had risen by 30 cm.
Data from the TerraSAR-X radar satellite before and after the changes has confirmed the localised nature of the situation. "A geochemical process called anhydrite swelling has been confirmed as the cause of these uplifts. This is a transformation of the mineral anhydrite (anhydrous calcium sulphate) into gypsum (hydrous calcium sulphate). A pre-condition for this transformation is that the anhydrite is in contact with water, which is then stored in its crystalline structure."
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