Rock salt lies in thick beds below this part of Maceió, and it was extracted by solution mining - pumping water down, dissolving the halite, drawing the brine back up, and leaving voids behind. Dozens of cavities were worked beneath the northern districts by the petrochemical company Braskem. Salt creeps under pressure; the roof of a cavern that is not properly managed will sag and eventually break, and the failure travels upward through the overlying rock until it reaches the surface as a slow, wide bowl of subsidence rather than a sudden hole. The warnings were not new. Two professors at the Federal University of Alagoas raised the risk as far back as the 1980s, and university researchers had been publishing on it since at least 2010. Almost nobody outside the university was listening.

It took the state until May 2019 to put a formal finding on the record. The Geological Survey of Brazil - the CPRM, a federal research body under the Ministry of Mines and Energy - presented its report at the Federal Court in Alagoas and concluded that the ground movement in Maceió was linked to the mining. Extraction, the survey found, had been carried out in a way that destabilised the existing cavities and produced the fissuring above them. It is worth being precise about what that document did and did not do. It established a geological connection between the mining and the subsidence. It did not, by itself, settle the questions of liability that courts in two countries have been working through ever since.

What followed has no real precedent in urban Brazil. Five neighbourhoods - Pinheiro, Mutange, Bebedouro, Bom Parto and part of Farol - were progressively condemned and evacuated. Estimates of the human scale vary because nobody set out to count this in advance: figures from the city and from monitoring bodies put the number of people who have had to leave since 2018 at somewhere between fifty-five and sixty-four thousand, with roughly fourteen thousand properties given up. In May 2022 the municipality asked the national statistics institute, the IBGE, for help simply establishing who had been affected. Walk these streets now and the doors still have numbers, the bougainvillea still grows over the walls, and the schools stand with their gates chained. Among the losses are listed heritage buildings: the Solar Nunes Leite, built between 1880 and 1890, and the 1877 asylum founded for orphans of the Paraguayan War, which was still working as a public school when the ground began to move.

For five years the disaster moved at the speed of geology, which is to say slowly enough that it kept slipping out of the national news. Then, on 30 November 2023, Maceió declared a 180-day state of emergency over the imminent collapse of a mine beneath Mutange. A perimeter went up, and people who had already been told to leave watched from behind it. On 10 December 2023 the city's civil defence authority confirmed that the mine had partially collapsed. No deaths were reported; the area had already been emptied - which is the single clearest argument for taking slow disasters seriously. But the collapse also ended any lingering hope among former residents that the ground would settle and the neighbourhoods could be reoccupied.

Braskem has not officially accepted that it caused the disaster. It has nonetheless signed agreements in the Alagoas courts committing more than twelve billion reais to compensating residents and business owners and to relocating public facilities such as schools and health units. The case has travelled: in May 2022 affected residents were heard by the District Court of Rotterdam, which ruled that September that it had jurisdiction, three Braskem subsidiaries operating on Dutch territory. On 1 November 2024, Brazil's Federal Police indicted twenty people connected to the company on charges relating to damage to public property and environmental crime - charges, not findings. All of which is the formal register, and the formal register is not where this is felt. A payment closes a file. It does not restore the street a family lived on, the neighbours they knew, or the reasonable expectation that the ground beneath a house in a capital city will stay where it is.