The World Got Diamonds. A Mining Town Got Buried in Sludge.

JAGERSFONTEIN, South Africa — The dirt wall holding in mucky waste from diamond mining grew over the years to resemble a wide, towering plateau. Suspended like a frozen tsunami over neat tracts of Monopoly-like homes in the rural South African mining town of Jagersfontein, the dam alarmed residents who feared it may collapse.

“We saw it long time, that one day this thing will burst,” said Memane Paulus, a machine operator at the dam for the past decade.

The worst fears of residents came true this month when a section of the dam crumbled, sending a thunderous rush of gray sludge through the community that killed at least one person, destroyed 164 houses, and turned a six-mile stretch of neighborhoods and grassy fields into an ashen wasteland.

The Jagersfontein disaster has caused alarm in a nation where heaping dams of mining waste, known as tailings, are part of the landscape. Experts estimate that South Africa has hundreds of tailings dams, which mining watchdogs say is the legacy of an exploitative industry that extracts lucrative gems for jewelry stores abroad, while poor communities are saddled with toxic waste at home.

The townspeople in Jagersfontein, home to one of the world’s oldest diamond mines, had watched the wall of waste mount, looming over their homes and streets. But there was little they could do to stop it because it was big business.

A consortium that bought the mining waste from the mine’s former owner, De Beers, was sifting through the tailings to extract any diamonds left behind — an increasingly popular offshoot of mining. In doing so, the operation was piling up even more waste, and government oversight was lax. Some mine workers were scared when their colleagues reported finding leaks in the dam.

“It was definitely avoidable,” said Mariette Liefferink, chief executive of the Federation for a Sustainable Environment, an environmental organization focused on mining. “The damage to the ecosystem, to human lives, to future generations — the risks are significant.”

The international mining industry had promised to do better after a similar dam collapse in Brazil three years ago killed more than 250 people. Some of the leading mine operators collaborated to develop standards for tailings dams. But many smaller operators, like the one in Jagersfontein, don’t follow the standards and lack the resources and expertise to manage tailings dams, Ms. Liefferink said.

Marius de Villiers, the legal compliance officer for the mine’s operating company, Jagersfontein Development, said it complied with all requirements set by South African regulators. The dam was regularly inspected, he said, and an engineering report from July declared it was structurally sound.

“We were not even contemplating that something like this would happen,” Mr. de Villiers said. He said that while the company was still investigating the dam break, it “must accept liability that comes with the operations and with the break.”

‘That thing is going to blast’

At about 2 a.m. on Sunday, Sept. 11, a truck driver at the dam spotted a crack in the facade, several workers there that day said in interviews. The driver reported it to a foreman, who checked it out but did not do anything, the workers said.

Joe Makalajane, a pan operator at the mine, did not see the crack himself but spoke to the driver as they were ending their shift, he said.

“He said, ‘I’ll tell you, that thing is going to blast,’” said Mr. Makalajane, 45, recalling his conversation. Of management, he added, “They didn’t take it seriously.”

Mr. de Villiers and Johan Combrink, the plant manager, denied that there was any report of a crack early that morning.

The dam wall collapsed between 6 and 7 a.m. Some residents are furious at the prospect that they could have been alerted earlier.

Rio-Rita Breytenbach, whose home is near the dam, stood on a chair in the kitchen as the barrage of slime barreled toward her. She was swept off the chair and out of the house. Caught in the raging current, Ms. Breytenbach, 39, said she floated on her back and paddled in the muck to keep her head above water.

“I was praying that I would survive,” she said.

She finally came to rest on a farm, where the police found her — more than six miles from her house.

The sludge wiped out much of two residential neighborhoods to the south and the east. Fields, stretching for miles, looked like frozen cement lakes, some dotted with mangled cars and sunken utility poles.

Jack Sephaka was visiting his mother across town when the dam broke. He stared from a distance in horror — his three-bedroom house was being washed away with, as far as he knew, his wife and one of his sons inside.

“I thought they were dead,” he said.

To his relief, his wife eventually called his mother to say they had made it to a shelter.

Now he has to rebuild a home that he bought 20 years ago for 40,000 rand ($2,300), now missing its entire front facade.

Mr. Sephaka had worked at the mine shortly after it reopened in 2010, but quit after four years because conditions were bad, he said.

“I was not happy,” he said, with “the stress of the mine.”

But the mine’s problems still caught up to him.

A colonial past

With its first diamonds extracted in 1870 by colonial settlers, the Jagersfontein mine is a relic of a diamond rush that often exploited Black South Africans while enriching white owners. It yielded a 650-carat diamond, among the world’s largest, that was acquired by British merchants and from which was cut the jubilee diamond, named in honor of Queen Victoria’s diamond jubilee.

De Beers, the global mining titan, operated the mine from 1932 to 1971. It then sat idle, but in the early 2000s, De Beers sought to capitalize on improving technology to extract minerals from tailings. It sued for the right to mine tailings without a mining license and won a judgment in 2007.

De Beers then sold the tailings at Jagersfontein in 2010 to a consortium that eventually came under the control of Johann Rupert, a South African billionaire whose companies own luxury brands like Cartier and Van Cleef & Arpels. In April, just six months before the collapse, Mr. Rupert’s holding company, Reinet Investments S.C.A., sold all of its shares in Jagersfontein Development to Stargems, a Dubai-based diamond manufacturer and retailer, according to a Stargems announcement.

Reinet did not respond to requests for comment.

The companies could be prosecuted for violating South Africa’s environmental and water laws, or could be forced to pay compensation, said Tracy-Lynn Field, a law professor at the University of the Witwatersrand in Johannesburg who specializes in environmental and mining law. Government officials may also have to answer, she said.

The ruling in 2007 in De Beers’s lawsuit removed responsibility for tailings dams from the government’s minerals department. Instead, because tailings are processed in dams, the Department of Water and Sanitation was left to oversee them, despite limited expertise in mining, Ms. Field said.

Warning signs

Residents said they were excited when the mine roared back to life in 2010, believing it would create jobs.

But soon they were coughing from all the dust in the air, and watching with angst as the dam’s dirt facade nearly doubled in height.

“We kept saying, ‘What if something happens here? What if it breaks?’” said Itumeleng Monageng, 28, who unfortunately found out the answer: This month he was knee-high in muck, salvaging whatever he could from his home.

Fears heightened in recent years when residents said they periodically saw water seeping through the dam wall. The mayor of Jagersfontein, Xolani Tseletsele, said community members aired their concerns with officials from the water department.

But Mr. Combrink, the plant manager, denied that the dam ever had a leakage problem, or that employees had reported holes in the facade. He attributed any moisture to storm water runoff.

According to a copy of a water department directive, inspectors visited the dam, and in January 2021, ordered the operation to stop, citing several violations. Chief among them was that the facility disposed more than two and a half times as much waste in the dam as it was allowed to in 2020 — and had continued disposing waste even after department officials told it to stop.

Five months later, the department cleared the facility to reopen, noting in a memorandum that Jagersfontein Development had agreed to be inspected more closely and installed new equipment to reduce the waste water disposed in the dam. Although the water department said in its memo that Jagersfontein Development still needed to address issues of dam safety raised in an independent engineering report, it gave no directive or deadline for the company to do so.

Richard Spoor, an attorney with decades of experience litigating mining cases, said it was extraordinary that water department officials, “having found that that high-level report showed a serious risk,” allowed it to reopen.

Sputnik Ratau, a spokesman for the water department, said that the dam had been allowed to reopen while safety issues were being addressed because dam officials had already satisfied other conditions.

In 2018, Jagersfontein Development built a new section of the dam that would increase its capacity by 30 percent and increase profitability, according to a 2019 annual report filed by Reinet Investments.

Even with that expansion, the dam was still having capacity issues — it has applied for a permit to dump waste in the original mining pit, which is a national heritage site.

An analysis of satellite images conducted after the collapse by a data and analytics company shows that from Aug. 1 to 13, the corner of the dam that broke had become slightly deformed, indicating weakness, said Dave Petley, a geologistat the University of Hull in England. The new section is the one that collapsed, he said.

Mining companies and regulators with proper expertise should have caught those warning signs, he said.

For Mr. Sephaka, the former mine worker whose house was ruined, this was the latest sour chapter in the long life of a mine that he felt had brought little benefit to the community.

“It’s painful,” he said, surveying the wreckage.

John Eligon reported from Jagersfontein, and Lynsey Chutel from Johannesburg.