Ajka Red Mud Spill 2010 (Kolontár), Hungary: Case Study

Reference article · Updated 2026-11-06

Key facts

The failure occurred on 4 October 2010 at a reservoir of the MAL alumina plant near Ajka; the north-western corner of the reservoir gave way.
Ten people died; reported injuries range from about 150 to about 200.
The red mud was strongly alkaline, with a pH reported at about 13; released volume is given as 600,000 to about 1 million m3, depending on the source.
A 2019 retrial at Győr convicted ten defendants, including former company executives, and acquitted five.

Red mud and why it is stored in reservoirs

Aluminium is made from bauxite in a two-step process: the Bayer process first dissolves alumina from the ore in hot sodium hydroxide, and the insoluble residue is then discarded. This residue, known as red mud or bauxite residue, is fine-grained, contains iron oxides that give it its colour, and remains strongly alkaline because of the caustic liquor. Producers have long kept it in engineered reservoirs, some of which are built much like tailings dams.

Red mud is not radioactive in any way that matters for this case, and the Ajka accident has no uranium connection. It is included in this reference because the hazard is of the same type as a tailings failure: a large stored volume of fine waste and process liquid held by an embankment, with an extended downstream flow path. The wider family of such events is listed in the chronology of tailings dam failures.

The failure of 4 October 2010

A geotechnical case study by engineers of Fugro Consult dates the event to 4 October 2010 and describes the north-western corner of reservoir X, also numbered as reservoir 10, giving way. Hungarian authorities, in a presentation to a UNECE conference, gave the released quantity as 600,000 to 700,000 m³ of red mud and process water. Other accounts put the flow near 1 million m³ from a reservoir said to hold about 30 million m³, and the 2019 court coverage uses about 1 million to 1.1 million. The spread illustrates why no single figure should be quoted without its source.

The wave inundated the settlements of Kolontár and Devecser and a wider area reported at more than 40 square kilometres. The Hungarian presentation records ten deaths and 790 affected people. Press reports early in the emergency gave lower casualty numbers, which rose as the toll was confirmed.

Chemical hazard: alkalinity, burns and the Danube

The Hungarian presentation describes the mud as having a pH of about 13 because of sodium hydroxide. The main immediate dangers were therefore chemical burns to skin and eyes, and the physical force of the flow. In the days that followed, authorities and the International Commission for the Protection of the Danube River (ICPDR) framed the main environmental questions as high pH and heavy metals in the river system.

Press reports citing official measurements stated that the pH where the slurry entered the Danube was about 9 to 10 and that the river's pH at a downstream station was later close to neutral. Authorities also warned people not to let animals drink from affected waters in the immediate aftermath.

Emergency response

Residents of Kolontár were evacuated, and Devecser residents were told to prepare to leave because the remaining north wall of the reservoir was expected to fail again. The sources reviewed for this page do not give verified details of the later cleanup, its cost or the volume of material removed, so none are stated here.

Why did the wall fail?

The sources reviewed do not give a single settled answer. The Fugro case study attributes the failure to poor siting: the reservoir lay partly on a diverted creek bed and on marshy ground weakened by the highly alkaline liquor, on a sloping site. Official statements in the early days suggested human error, and there were press reports that wind pressure on the walls was considered. Anyone seeking detail should treat these as competing hypotheses and read the technical papers directly.

General principles for foundation and water-balance problems are set out on the page about tailings dam safety.

Legal and regulatory aftermath

The criminal case took nine years. A Veszprém court acquitted all defendants in January 2016; an appeals court overturned that ruling in February 2017 and ordered a retrial. In February 2019 a court in Győr found ten defendants guilty and acquitted five. The former chief executive of the company, Zoltán Bakonyi, was sentenced to two and a half years in prison and his deputy to two years, as reported by several news services. Commentators noted that this was the first time company officials in Hungary were jailed for criminal negligence in an environmental disaster.

On the civil side, the company was reportedly ordered to pay a very large sum for environmental damage and was later put into liquidation. The exact amount and the sequence of administrative decisions are best confirmed from Hungarian court records. Comparable questions of operator responsibility arose after the failure at Stava in 1985.

Why the numbers differ between sources

Readers comparing accounts of Ajka will find different figures for volume, injuries and affected area. Volume estimates depend on whether the count refers to red mud alone or to mud and liquid, and on whether it is derived from the reservoir's pre-failure level or measured in the field. Injury counts were reported as about 150 in some reports and about 200 in others, and the number of dead moved as victims died of their injuries in the days after the flood.

Early news reports also quoted figures such as two million cubic metres that later reporting did not support. For a reference page the safest approach is to give ranges and name the source: the Hungarian presentation to the UNECE conference for the official figures, and the court reporting for the legal chronology.

Relevance for tailings management

Ajka showed that an alkaline residue store can fail with the same dynamics as a mine tailings dam, and that a downstream population within a few kilometres has little warning time. It also illustrated the importance of emergency plans and of rapid, public environmental sampling. These themes are developed in monitoring and surveillance of tailings dams.

Frequently asked questions

When did the Ajka red mud accident happen?

On 4 October 2010, when the north-western corner of a red mud reservoir near Kolontár, Hungary, collapsed.

How many people died?

Ten people died, according to the Hungarian presentation to the UNECE conference and later court reporting.

How much red mud was released?

Official Hungarian figures cite 600,000 to 700,000 cubic metres of mud and liquid; other sources report close to 1 million. The figure depends on the source.

Was the spill radioactive?

No. Red mud is the residue of aluminium refining, and the main hazard was its strong alkalinity, about pH 13, along with the force of the flood.

Were executives convicted?

In February 2019 a Győr court convicted ten defendants, including former company executives, and acquitted five, after an earlier acquittal was overturned on appeal.