38 years ago today: The Tesero dam burst: mudslide kills more than 260 people

July 19, 1985 is a sunny day in the Italian municipality of Tesero.

38 years ago today: The Tesero dam burst: mudslide kills more than 260 people

July 19, 1985 is a sunny day in the Italian municipality of Tesero. The region in the Stava valley near Trento is popular with holidaymakers. Nobody suspects that a catastrophe is looming higher up in the mountains.

Fluorite has been mined in the Prestavèl mine in the Zanggenberg massif between 1900 and 1500 meters above sea level for decades. When the valuable chemical substance is broken down, huge amounts of very liquid sludge from sand and water are produced. This is directed to two storage and clarification tanks, one on top of the other, about 50 meters deep, consisting of large sand dams that were built about 20 years ago - from tamped earth, which is from time to time paved with bulldozers. A wooden construction that supports the earth wall is missing. It's just one of many factors contributing to one of the greatest disasters in Italian industrial history.

It is 12:22 p.m. on that fateful Saturday when suddenly and without warning, the upper dam bursts. It spills into the dam below, which collapses under the weight. 180,000 cubic meters of mud, sand and water race down the valley at 25 meters per second.

First, the thunderous mudslide hits the small community of Stava, then Tesero, about three and a half kilometers away. With brutal force, the torrent sweeps away everything in its way: trees, cars, entire streets, houses, farmsteads and sawmills. The wave is so high that it smashes over an almost 30 meter high antique stone bridge that has stood in the village for ten centuries. It is almost completely destroyed. Around three and a half minutes after the accident began, the mud in the Avisio river comes to a standstill. The beautiful Stava valley is just a muddy wasteland. An area of ​​435,000 square meters is covered over a length of around 4.2 kilometers by a layer of mud that is up to 40 centimeters thick in some places. The 2500 inhabitants and also a number of tourists have almost no chance. 268 people die, including almost 60 children and young people.

It doesn't take long for rescue workers to arrive in the community. The first are the Volunteer Fire Brigades of Tesero and Val di Fiemme. Other fire brigades, soldiers, rescue services from the White and Red Cross, rescue divers, police with dog units, forest corps and countless volunteers follow. In the end, there are at least 18,000 people who tirelessly search for victims over the following hours and days. Even in the dark, they work in the light of the headlights, clearing away rubble and masses of mud with pickaxes and shovels.

Tesero City Hall becomes the headquarters from which the rescue operation is coordinated. The search operation lasted three weeks. The local elementary school gym becomes a morgue. Around 1,000 Red Cross volunteers are on duty for days to help the relatives identify the victims. In the cemetery of the small community of Tesero, there is not enough space for the many dead, so the victims are also buried in the neighboring towns.

It's a heavy blow to the otherwise peaceful town. The survivors are left in shock and sadness for their friends and loved ones. But how could a catastrophe of such proportions have happened in the first place?

The fact is: 1985 was one of the rainiest years in the Stava valley since weather records began. There is almost 23 percent more rain than usual. In addition, the snow that falls in the Alps during the winter melts in the spring – within just a few weeks. A team of experts later calculated that the volume of water from the thaw was above average that year. Some of the meltwater flowed down the slopes and through the rivers, streams and underground springs into the clarifiers, causing a further rise in water there. All these circumstances apparently played a role in increasing the volume of water in the dam basin.

But why wasn't the water drained from the pool through a drainage pipe as usual? The investigators go in search of clues in the muddy remains and sift through the remains of the dams. After sifting through 360,000 tons of mud, they find the pipe. But that's broken. Your research reveals that a section was replaced in a previous repair. But the weight of the settled sediments has caused the pipe to sag over the years. The pipe was probably bent out of the socket in such a way that the sewage could escape inside the basin and the entire drainage system became ineffective.

Six months before the disaster, sand had already slid from the upper dam basin, creating a 20-metre hole through which water had escaped. Only after two months was the gap provisionally patched up. In May, both pools had to be drained for further repairs. The draining water could have made the pipe even more unstable and caused even larger gaps. Three weeks before the dam collapsed, the basins were refilled with water. The system went back into operation four days earlier. The waste water was fed into the basins, but the excess water could not drain away due to the defective drainage pipe. Then there was the rain and the thaw, until at some point the pressure became too great. Because water had already penetrated to the outside, the sand was wet and the dam unstable.

In addition, the investigators find out that experts have been monitoring the security checks since 1974, but these apparently only took place inadequately. According to the documents, even then the angle of inclination of the upper dam was no longer within the norm. Sufficient stability was therefore not guaranteed for the reservoir. A stability test in 1975 found that the slope of the dam in the upper basin was "extraordinary" and the stability was "limited". Despite this, the mining company gave a positive response to the Mine Inspectorate and the latter to the municipality, so the landfill was further elevated - albeit with a lesser slope of the dam.

But the subsoil was apparently completely unsuitable for supporting the dams. The ground was too swampy to ensure adequate drainage - important for stability. Without sufficient irrigation, the dams could not dry out and thus become solid. In addition, the foundations for the upper dam partly protruded into the lower basin - so the upper dam was built on the sediments of the lower basin instead of solid ground. The Ministerial Commission of Inquiry and the experts appointed by the Court of Trento stated that "the entire landfill posed a constant threat to the valley below".

In 1988 the process was opened. In June 1992, ten people were found guilty of negligent causation of a disaster and multiple manslaughter. Of these, eight were responsible employees of the companies that had operated the mine since the basins were built. Two were local authority employees responsible for security. All were sentenced to prison terms. The judges noted in their verdict that a tenth of the legal costs would have been enough to secure the pools in such a way that a disaster would not have occurred. The damages totaling more than 132 million euros in favor of 739 injured parties were paid almost in full in 2004 as part of an out-of-court settlement.

Today, a foundation commemorates the accident 38 years ago through various educational projects and educational work. There is also an information center with a nature trail on site. Every year a prayer is held and a commemorative mass is celebrated. However, the foundation does not want to limit itself to a "contemplative commemoration of the tragic events," says the website. Rather, they want to "contribute to raising awareness and promote the sense of responsibility that was missing in Stava at the time".

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Sources: Stava Foundation, National Geographic, DPA archival footage