That Sinking Feeling: Buildings Crack Up as Black Forest Town Subsides

By Mark Waffel in Berlin

In the last six months mysterious cracks have appeared in buildings in a picturesque Black Forest town. As the cracks have grown, so have residents' concerns. The problem is the town is slowly sinking into the ground. A geothermal project is apparently to blame.

People living in the small town of Staufen could be forgiven for having that sinking feeling. The citizens of Staufen, a picturesque town on the edge of the Black Forest in southern Germany, have good reason to feel worried: parts of their historic town center are slowly sinking into the ground.

As the earth beneath the town has given way, large cracks have appeared in the town hall, a church, two schools and over 50 homes. The first of the mysterious cracks, which have got bigger and bigger, was spotted two weeks after the town council embarked on an innovative geothermal project.

But what happened next took the forward-thinking town council by surprise. By trying to do its bit for the environment, the council appears to have upset a delicate balance. A couple of weeks after carrying out the work, the first cracks in the facade of buildings started to appear. So far, Staufen Mayor Michael Benitz told SPIEGEL ONLINE, the damage has been primarily cosmetic. "No buildings are in danger of collapsing," he said.

The problems began when, as part of the refurbishment of the town hall -- built in 1546 -- the council decided to heat the building with geothermal power from deep below the earth's surface. In September last year an Austrian company sunk seven geothermal probes 140 meters into the ground.

Six Figure Damage

Not long later, the first cracks began to appear, and the number of buildings whose facades have cracked open has risen steadily. At last count 68 buildings in the town center have been damaged. The cost of repairs, the mayor said, will run into six figures.

The damage has been caused by parts of the town sinking into the ground -- very slowly. To measure movements in the earth beneath Staufen, officials have set up 30 monitoring points. While some areas of the town have sunk by up to eight millimeters, other parts have actually risen by a few millimeters.

Although officials are certain the cracks have been caused by the town sinking, tests are still being carried out to find out why the earth beneath Staufen has given way. But for most residents, it seems, the culprit is clear: the town council's geothermal project.

Robert Breder, a structural engineer -- who has been hired by the town to look into the cause -- told SPIEGEL ONLINE that he also suspects the town's environmental ambitions are to blame. Even though natural causes could not be ruled out, he said, the fact that the cracks appeared shortly after the probes had been sunk certainly seemed indicative.

According to Breder, when the geothermal probes were sunk into the ground, the contractors came across confined groundwater. It is possible, he said, that the digging might have reduced the water's pressure and caused some of it to trickle away. As a result, the earth's surface could have sunk.

Breder added that although it was fairly common for geothermal projects to cause very minor damage to buildings -- especially ones with structural problems -- the damage to buildings in Staufen was unusual. "I have never encountered anything like this -- not to this extent," he said. "Also colleagues who I've spoken to about this have not seen anything like this."

The town's 8,000 residents are now waiting to see what will happen next. Repairs to buildings cannot start before the cause has been conclusively established and the town stops sinking. Mayor Benitz said it was still too early to say how severe the damage will be in the end.

"Will the earth continue to sink or is it going to stop?" he wondered. "If it does stop now, then we will have got away lightly, but if it does continue it could turn out to be quite bad."

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