Tailings Dam Safety: Why Dams Fail and Key Risk Factors

Reference article · Updated 2026-11-06

Key facts

Overtopping is usually the final event in a cluster of contributing factors, not an isolated root cause, according to reviews of ICOLD data.
Dams are raised by the upstream, downstream or centreline method; the upstream method rests new lifts on previously deposited tailings and is the most vulnerable.
Brazil prohibited new upstream dams in February 2019 after the Brumadinho failure.
The Global Industry Standard on Tailings Management was launched on 5 August 2020 and applies to existing and future facilities.

Schematic cross-sections of the three common raising methods for tailings dams. Original schematic, not to scale.

The main physical mechanisms of failure

Engineering reviews of historical failures classify the immediate mechanisms in broadly similar ways. The categories used in the review by Rico and colleagues, based on an ICOLD synthesis of 221 incidents, include seismic liquefaction, rise of the phreatic surface, slope instability or mass movement, piping and seepage, overtopping, and foundation failure.

Overtopping. Water rises over the crest because the pond has too little freeboard or the spillway cannot cope with a storm. Merriespruit, South Africa (1994), failed this way after heavy rain.
Foundation failure. The ground beneath the embankment is weaker than assumed. The independent panel on Mount Polley, Canada (2014), concluded that the breach resulted from failure of a glaciolacustrine layer in the foundation and found no evidence of overtopping or internal erosion.
Seepage and piping. Water finds a path through or under the dam and erodes soil from within. Poor drains or blocked decant pipes raise the water pressure that drives this process, as discussed in analyses of Stava.
Slope instability and liquefaction. Saturated, loose tailings can lose strength suddenly under stress or shaking. The review panel on the Fundão dam in Brazil (2015) reported that small seismic shocks triggered a collapse that was already well advanced because of design and maintenance weaknesses.
Earthquake loading. Ground motion can trigger liquefaction or slope movement; design standards require a seismic design basis proportional to the consequence class.

Reviews of the ICOLD database also stress that many failures have more than one contributing factor and that causes in historical records are frequently unknown or poorly documented. Overtopping, in particular, is commonly the end of a chain of events rather than the starting point.

Upstream, downstream and centreline construction

Most tailings dams are built in stages. A starter dyke is raised as tailings accumulate, and the method used to raise it determines how the dam behaves.

Upstream. Each new lift is founded partly on the beach of previously deposited tailings. It is the cheapest and quickest method, but the dam depends on the strength of loose, often saturated tailings, which can liquefy.
Downstream. Lifts are placed on the downstream side so that the embankment rests on competent ground and on its own fill. It needs more material and a larger footprint, and gives better control of drainage and seismic behaviour.
Centreline. The crest is raised vertically above the starter dyke. Behaviour lies between the two other methods.

The Stava bank was raised by the upstream method according to the case study cited on this site. After the Brumadinho failure, Brazil's National Mining Agency issued a regulation in February 2019 banning new upstream dams and requiring existing ones to be decommissioned on a fixed timetable; reported deadlines were later adjusted, so the current schedule should be taken from the official text. A review that compared incident records noted that upstream dams account for a large share of recorded incidents, though the share varies by study.

Management, oversight and the human factors

A published review of ICOLD data by Azam and Li (2010) separated physical failure modes from climatic and managerial causes and found that unusual rain and poor management feature prominently. The case histories fit this view. At Stava, no serious stability checks had been carried out for more than twenty years. At Church Rock, cracks seen before the 1979 breach had been sealed but not explained, as described on the page on uranium mill tailings dam failures. At Mount Polley the panel judged that regulatory inspections would not have prevented the failure, because the root problem lay in design and site characterisation, a reminder that inspection alone cannot replace sound design.

Typical weaknesses highlighted in investigations include incomplete site investigation, a design basis that does not follow the real operating history, changes in the plan for raising the dam without re-analysis, poor water balance, and unclear accountability between owner, designer and regulator.

Hazard, consequence classification and downstream exposure

Dam safety practice separates the likelihood of failure from its consequences. Consequence classification considers the people downstream, environmental and cultural receptors and economic losses, and it sets the design standards: stricter flood and seismic design criteria and more intensive surveillance for dams in higher classes. The record in the chronology of major failures shows why. The failures with the highest death tolls were those with homes, hotels or workplaces in the flow path.

For uranium operations the consequence assessment includes radiological pathways, including contamination of floodplain soils and surface water by long-lived radionuclides.

Safety frameworks and standards

Several layers of guidance apply to tailings dams.

Global Industry Standard on Tailings Management (GISTM). Launched on 5 August 2020 by the Global Tailings Review, co-convened by the International Council on Mining and Metals, UNEP and the Principles for Responsible Investment. It was prompted by the Brumadinho failure, applies to existing and future facilities regardless of location, and covers topics including affected communities, design and monitoring, governance and emergency response. ICMM members committed to meet it for facilities with extreme or very high potential consequences by August 2023 and for all others by August 2025.
ICOLD. The International Commission on Large Dams publishes bulletins on tailings dam design, incidents and monitoring and maintains the incident database used by many reviews.
National guidance. Examples include the Canadian Dam Association's 2014 technical bulletin applying its dam safety guidelines to mining dams, and the Mining Association of Canada's guide to tailings management, first published in 1998.
Regulation. National laws and regulators specify design criteria, independent review and closure obligations; see regulation of uranium mining, tailings and radiation protection.

Day-to-day practice for detecting problems early is described on the page on monitoring and surveillance.

How to read failure statistics

Statistics on causes and frequency depend heavily on the database used. ICOLD, academic compilations and activist-maintained lists use different thresholds for what counts as an incident, and many older failures lack a documented cause. Percentages for individual causes in secondary articles often derive from one of these sets and cannot be compared with another. This page therefore gives no single failure rate; readers should consult the underlying papers and the ICOLD publications to find the scope of each dataset.

Frequently asked questions

What is the most common cause of tailings dam failure?

There is no single answer. Reviews of ICOLD data list overtopping, slope instability, foundation failure, seepage and earthquakes, and note that many failures involve several factors and that some causes are unknown.

Why is the upstream construction method considered riskier?

Each new lift is partly supported by earlier, loose tailings that can be saturated and liquefy, so safety depends on the strength of the waste itself.

Has any country banned upstream tailings dams?

Brazil's National Mining Agency banned new upstream dams in February 2019 after Brumadinho and required existing ones to be decommissioned on a timetable.

What is the Global Industry Standard on Tailings Management?

A standard launched on 5 August 2020 by the Global Tailings Review, co-convened by ICMM, UNEP and PRI, applying to existing and future tailings facilities worldwide.

Can inspections alone prevent failures?

Not always. The Mount Polley panel concluded that regulatory inspections would not have prevented that failure, whose cause lay in design and ground investigation.