Staßfurt dug 3 million cubic metres of salt out of the ground. Then it caved in.

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On 26 June 1899 the ground gave way above a salt mine in Leopoldshall, right next to Staßfurt in Saxony-Anhalt. The hole was 140 metres across and 40 metres deep. Beneath the neighbouring old town of Staßfurt, salt had been mined since 1852, and since 1883 the ground there has sunk by more than six metres. Several hundred buildings had to go, among them the town hall and the parish church. Where the market square used to be, there is now a lake. Our new episode takes just over 16 minutes to show how this happened and why Staßfurt is still sinking, even though its first mines have been full of water for more than a hundred years.

The salt nobody wanted

A saltworks is recorded in Staßfurt as early as 1170. In 1843 a borehole sunk in search of rock salt struck a salt deposit at almost 250 metres. In December 1851 work began on two shafts named von der Heydt and von Manteuffel, and on 31 January 1852 salt mining was formally opened. These two shafts are regarded as the first potash shafts in the world.

Cutting through the deposit in 1856, the miners found other salts above the rock salt that nobody wanted. Around 600 tonnes went onto the spoil heap as worthless “Abraumsalz”, waste salt. In the same year the chemist Heinrich Rose described one of these salts and named it after von Carnall, the mining official who had proposed the shafts. It is still called carnallite, and it contains potassium. Adolph Frank, a chemist at a Staßfurt sugar factory, found a way to extract it. He received his patent in 1861 and opened the first potash factory that October, and by 1863 there were already 18 such works in and around Staßfurt. To this day around nine out of every ten tonnes of potash end up as fertiliser.

The salt itself comes from the Zechstein Sea, which evaporated between England and Poland a little over 250 million years ago. Beneath Staßfurt it has risen into an arch, an anticline, which brings it close to the groundwater. And salt dissolves in water.

The ground gives way

The first warning signs came from Leopoldshall, now part of Staßfurt. Miners there were working a richer potash salt called kainite, almost up to the top of the salt body and with pillars that were too weak. From 1878 the pillars began to fail, and in 1879 a mined area of about 20,000 square metres collapsed. From 1880 the surface above the workings under the old town began to sink as well, and from 1883 Leopoldshall saw a series of Tagesbrüche, collapses that reach right up to the surface over a mined-out cavity. The largest, the one of 1899, later became an open-air saltwater pool, the Strandsolbad.

Mining beneath the old town ended in 1893. According to an expert report from 2018, it had left just over two million cubic metres of voids in the potash seam and just over one million in the rock salt. Added together, by our own calculation, that comes to just over three million cubic metres. Only part of it was ever backfilled. Around the turn of the year 1899/1900 so much brine seeped into the Leopoldshall mines that they were abandoned in the spring of 1900. In May 1900 the water reached the von der Heydt shaft, and in October the pumps were switched off.

11 November 1901

Mining carried on in newer shafts outside the old town. On 11 November 1901 a rock burst brought the rock crashing down in the Ludwig II salt mine. Seventeen miners died. Five were hewers, two were haulers, and ten were what the memorial calls Aushalter, young lads between 16 and 18 years old from Staßfurt, Leopoldshall, Neundorf and Hecklingen. A memorial stone with their names stands in the cemetery on Hecklinger Straße. Its inscription remembers the miners who died in the accident at Ludwig II. The town's old miners still keep that memory alive.

A leaning tower and a hall underground

From 1899 houses around the market square were torn down. In the middle of the subsidence stood the town church of St. Johannis with its 60-metre tower. The tower leaned until it stood 4.65 metres out of plumb, and it became known as the Leaning Tower of Staßfurt. The last service was held on 9 September 1906, and the church was later used as a barn. In May 1948 children were playing with fire inside, and the stored straw went up in flames. In 1964/65 the tower was taken down stone by stone, because it stood too close to homes to be blown up. Demolition of the old town hall began in 1966.

Potash mining around Staßfurt only ended on 31 December 1972, after which the last open mines were flooded. With them went a place you would hardly expect in a mine. At the Berlepsch-Maybach shafts, about 400 metres down, there was a festival hall some 80 metres long and 10 metres high. From 1934 a painting of Saint Barbara, the patron saint of miners, hung there. In 1975 the ground at Neustaßfurt caved in across 50,000 square metres and up to 34 metres deep. The site is still a closed zone today.

Why the town keeps sinking

The mines beneath the old town have been flooded for over a century, and yet the town is still sinking. Federal and state researchers studied this for years, partly with seismometers that have been listening since 1978. In 2008 they drilled from the Neumarkt down into the old workings. They found intact pillars, largely backfilled chambers and no large voids close to the surface. They see the subsidence mainly as a result of subrosion, the slow dissolving of salt at depth by groundwater.

Since 1907/09 the town has been pumping out groundwater, around 700 cubic metres a day according to a report from 2002. Without the pumps, parts of the centre would stand under water. Yet the pumping speeds up the subrosion. Staßfurt has to pump to stay dry, and in doing so it helps the ground to sink. At the Neumarkt the state office for geology and mining measures a long-term average of 2 to 14.5 millimetres a year, recently less, and considers a sudden collapse there very unlikely.

The town turned its subsidence into something you can see. It cleared the deepest part and let the groundwater rise. The concept went by the name “Aufheben der Mitte”. The lake opened in 2006, and the subsidence lines are marked along its shore. The story is not quite over. A research report from 2002 expected another stretch of water to form at Bernburger Straße around 2050.

What our map and our images show

In our data there are 16 shafts within five kilometres of the town centre and 37 within 15 kilometres. These are the shafts mapped in OpenStreetMap, not every shaft ever sunk. The 3D scenes in the episode are schematics based on expert reports and the specialist literature. In the subsidence scene the height is exaggerated four times, in the shaft scene the terrain five times, and both are stated in the picture. The scenes with people, including the 1899 collapse at the start, were generated with AI and are labelled “KI-Rekonstruktion” (AI reconstruction). The old photographs are genuine, as is an 1884 wood engraving of a collapse near Leopoldshall from the magazine “Die Gartenlaube”.

Going there yourself

The best place to start is the town lake, whose surface shows where the groundwater would settle if left alone. On its northern shore is the Kaligarten, the potash garden, with the sites of the first two shafts and a miners' monument from 1934. South of the lake the outline of the church tower has been set into the grass at a slant, and the town calls the spot the “Heiliger Rasen”, the holy lawn. The town and mining museum in the Salzgrafenhaus at Pestalozzistraße 6 shows a large mine model from the 19th century and the Saint Barbara painting from the underground hall. The Strandsolbad opens in summer. Please check opening times before you go.

You can no longer go underground in Staßfurt, as every mine there has flooded or been flooded. The site of the great collapse at Neustaßfurt is a closed zone, and old shaft sites and collapse areas are off limits too. The orecast map shows which shafts and mines are documented around Staßfurt, and the video tells the whole story in just over 16 minutes.

Illustrations generated with AI.