From potential hidden sinkholes to the weakening of concrete by salt water. Those are some of the plentiful hypotheses about what caused a residential building in Miami to suddenly collapse.

The partially collapsed Champlain Towers South building in Surfside was in the midst of a recertification process at 40 years old, something that requires detailed inspections, both structural and electrical.

A 2018 report from engineering firm Morabito Consultants – the same one that performs the 40-year inspections – identified numerous problems in the building, including “significant structural damage” to a concrete structural slab under the indoor pool, which needed extensive repairs.

“If the waterproofing is not replaced in the near future, the extent of concrete deterioration will expand exponentially,” warned the report, which was released along with other documents by Surfside officials. He warned that the situation represented a serious error dating from the original construction of the building.

The report also discovered “abundant cracks and spalling” in concrete columns, beams and walls in the parking lot. Some of the damage was minor, while others were severe: columns with the steel rebar exposed and deteriorated.

It was not immediately clear from the documents whether that issue or others identified in the report were ever resolved or played a role in the collapse. Frank Morabito, president of the firm, did not respond to an email seeking comment on Saturday.

Surveillance video captured the moment the structure collapses. At least one person died Thursday when part of a 12-story, 40-year-old residential building collapsed on a main street in Miami Beach. The images you will see can be disturbing to some people.

In an interview Friday, Surfside Mayor Charles Burkett said he was unsure whether the inspection had been completed, but said it may contain crucial clues.

“It should have been a very simple thing to do,” Burkett said. “Buildings in America don’t collapse like this. There is a reason. We have to determine that reason.”

The collapse of the 12-story tower left many questions about how the tragedy could have happened and if other similar buildings are in danger.

Details of the Champlain Towers recertification inspection will be released once it is complete, Surfside City Clerk Sandra McCready said in an email.

Miami-Dade Mayor Daniella Levine Cava told a news conference Friday that she has seen no evidence of a sinkhole – much more common in other parts of Florida – or anything voluntary, such as a bomb.

“I can tell you right now that they have found no evidence of an intentional act.”

Other than that, a lot of attention is paid to seawater, the level of which is rising in South Florida and elsewhere due to changes in the weather. Last year, Republican Gov. Ron DeSantis signed a law to require builders to conduct sea level rise studies before starting publicly funded projects.

Like everyone else, the governor says he wants answers on the cause of the collapse, as soon as possible.

“We need a definitive answer on how this could happen,” DeSantis said at a news conference. “It is really a unique tragedy, in the middle of the night, that half a building collapses like this.”

Meanwhile, the land the building stands on has been gradually sinking, according to a study published last year by a professor of environmental studies at Florida International University.

But the professor, Shimon Wdowinski, cautioned that the collapse should not be attributed to that sinking land. Their study used satellite data collected between 1993 and 1999 to examine the land subsidence in Norfolk, Virginia; and in Miami Beach.

In a video interview released by the university, Wdowinski said the study found numerous examples of sunken land, some causing cracks in buildings, something he said is “quite common” in Florida.

“In most cases, those buildings just move,” he said. “There is no catastrophic collapse as in the case at Surfside, which was very unfortunate.”

Another hypothesis is that the ubiquitous salty water in an area that suffers from frequent flooding reaches the concrete supports, where it corrodes the corrugated steel bars and weakens the concrete.

Abi Aghayere, an engineering expert at Drexel University, said determining whether such deterioration occurred could be key to understanding the collapse.

“Did a column fail? That column has been bearing that load for 40 years. Why would it fail now? ”Said Aghayere, adding that it is rare for corrugated bars to corrode without anyone noticing. “You would have chunks of concrete protruding, falling off.”

Others have mentioned frequent flooding in the building’s underground parking lot, including the possibility that water has seeped through the porous rock that the area that includes Surfside and Miami Beach is in.

More than a day after the Miami Beach tragedy, authorities are working around the clock to locate survivors.

Surfside officials say work was underway on the building’s roof, but have dismissed the possibility that that caused the collapse. Barry Cohen, an attorney who escaped from Champlain Towers with his wife, said the work on the roof may have been part of a “perfect storm” of causes that combined to bring down the structure.

“They were making a new roof. And I think, all day, that the building was echoing, echoing and echoing. They have been doing it for over a month,” he said.

Another problem mentioned by some is construction on a nearby building, which they believe may have caused vibrations that weakened the Champlain Towers. Cohen said he raised concerns that the job could be causing cracks in the pool area.

The collapse has already sparked lawsuits, including one that was filed just hours later by attorney Brad Sohn against the condo owners’ association seeking compensation for negligence and other reasons on behalf of all residents of the building.

The association, the lawsuit says, “could have prevented the collapse of the Champlain Towers South tower with the exercise of ordinary care, security measures and supervision.”

A lawyer for the association, Ken Direktor, did not respond to an email seeking comment on Friday.