Stava Dam Disaster 1985: Causes, Victims, Verdict

Reference article · Updated 2026-11-06

Key facts

The dams held waste from fluorite mining above Stava, in the municipality of Tesero, Province of Trento.
The upper dam failed at about 12:22 on 19 July 1985; the flow travelled roughly 4.2 km at a speed reported near 90 km/h.
268 people died; three hotels, 53 homes and six industrial buildings were completely destroyed.
A criminal trial ended in June 1992 with ten convictions for multiple manslaughter and culpable catastrophe.

The valley, the mine and the two basins

Val di Stava lies in the Italian Alps near Tesero, in the Province of Trento. Fluorite from the Prestavèl mine and other mines was processed nearby, and the fine waste was pumped into two tailings basins built one above the other on the hillside. Below them, along a steep valley, stood the village of Stava, hotels and holiday homes that were full on a July Friday.

The basins were enlarged repeatedly over the years. According to the technical case study published by tailings.info, the bank was raised using the upstream method, which was the fastest and cheapest approach but also the most vulnerable, because each new bank rests partly on previously deposited, soft tailings. The general significance of this method is discussed on the page about causes of tailings dam failure.

The collapse of 19 July 1985

The Stava foundation's account dates the failure of the upper dam to 12:22 on 19 July 1985. The mass of saturated tailings poured into the lower basin, which also failed, and the combined flow ran down the valley. Published case studies give about 180,000 m³ released from the dams, with a further 40,000 to 50,000 m³ picked up from eroded ground, demolished buildings and uprooted trees. The flow moved at close to 90 km/h over about 4.2 km before it reached the Avisio river, covering an area of roughly 435,000 m² with mud 20 to 40 cm deep.

The same sources record 268 deaths. Three hotels, 53 homes and six industrial buildings were completely destroyed, eight bridges were demolished and nine buildings were seriously damaged. The economic damage is quoted at about 155 million euros in the case study. Because mud on this scale moves faster than people can flee, nearly all victims had no realistic chance of escape.

What the investigations found

Expert examination rejected two early hypotheses, an earthquake and an explosives blast at one of the regional mines. The findings that survive in the technical literature concern the design and operation of the basins:

The upper dam was below the minimum factor of safety needed to resist failure; the Stava foundation describes chronic instability, especially of the upper basin.
The deposited slimes were under-consolidated and did not settle, partly because the ground was marshy and the bank had been built in a way that impeded drainage.
The upper basin was built too close to the lower one, so its growing bank spread onto unconsolidated slime.
The upper bank was about 34 m high with an outer inclination near 40 degrees, standing on a slope averaging about 25 percent.
Drainage pipes were installed incorrectly, and the dams had received no serious stability checks or monitoring for more than twenty years.

Researchers have argued about the exact trigger. One analysis (Chandler and Tosatti) concluded that a blocked decant pipe within the tailings most likely initiated the collapse, while other analyses stress under-consolidation and excessive height and slope. The sources reviewed do not give a single agreed trigger, but they agree that the margin of safety was unacceptably low before any trigger acted. A report from 1974 is also cited as having described the dam's stability as marginal; its recommendations were not followed.

Trial and liability

The first trial took place in Trento and was concluded in less than three years, after which the case passed through several further levels of judgment, including the Supreme Court. According to the case study, the proceedings ended in June 1992 with ten people convicted of multiple manslaughter and culpable catastrophe. They included managers and officials responsible for building and running the upper basin and officials of the Mining District of the Autonomous Province of Trento who had not inspected the dams. Several companies, among them Montedison, and the Autonomous Province of Trento were ordered to pay damages.

The case is often cited as an early example of criminal responsibility reaching regulators as well as operators, because failure to inspect was itself part of the findings.

Lessons that carried into later practice

The disaster fed directly into the case for independent design review, regular stability analysis and instrumented monitoring of every tailings facility, topics treated in monitoring and surveillance of tailings dams. It also showed the importance of land-use planning below dams: the loss of life was so large because homes and hotels stood in the path of the flow.

Modern frameworks such as the Global Industry Standard on Tailings Management, launched in August 2020, address several of these themes through requirements on design, monitoring, governance and emergency response. For other failures set against Stava, see the chronology of major failures.

Why a tailings flow is so deadly

The numbers at Stava illustrate the physics of a tailings flow. A saturated mass of fine tailings does not spill like water; once its structure collapses it flows as a dense liquid, carrying boulders, trees and building debris. At the reported speed of near 90 km/h, a distance of about 4 km is covered in a few minutes, which is less time than any alert-and-evacuate chain could use. The depth of mud left on the valley floor, 20 to 40 cm over a large area, shows how far the flow spread out after the narrow valley section.

This is why dam safety frameworks treat the consequence of failure as separate from its probability: where a population lives directly below, only prevention is effective, and monitoring and design review have to be correspondingly strict. The same point arises in the Ajka case, where villages lay within a few kilometres of the reservoir.

Remembrance and documentation

A foundation created after the disaster maintains an archive and educational material about the event, and it is also the origin of a collection of case studies on other tailings failures. French accident databases and academic repositories hold technical papers on the dam geometry and the stability analyses carried out after the collapse. These documents remain the best routes for readers who want calculations rather than summaries.

Frequently asked questions

When and where did the Stava dam collapse happen?

On 19 July 1985, at about 12:22, in Val di Stava, municipality of Tesero, Province of Trento, in northern Italy.

How many people died at Stava?

The case studies and the memorial foundation record 268 deaths.

What was stored behind the dams?

Tailings from fluorite mining, deposited in two basins built one above the other.

What caused the failure?

Investigators found dams with an unacceptably low factor of safety, under-consolidated tailings, poor drainage and an overloaded upper bank. Researchers disagree on the precise trigger, with a blocked decant pipe proposed in one analysis.

Was anyone convicted?

Yes. The trial ended in June 1992 with ten convictions for multiple manslaughter and culpable catastrophe, and several companies and the Province of Trento were ordered to pay damages.