Zinc creep in cable spelter sockets brought down the Arecibo telescope in 2020

The 305-meter Arecibo telescope’s collapse in Puerto Rico in 2020 resulted from zinc slowly losing its grip on the cables supporting the heavy platform above the reflector dish, according to a National Academies investigation. The cables were anchored in sockets filled with zinc; as the metal crept over time, cable ends began pulling free, and the platform ultimately fell into the dish. The failure sequence appears to have accelerated after Hurricane Maria in 2017. Inspections afterward showed substantial, worsening cable pullout, but safety calculations following an earlier cable failure did not account for the time-dependent deterioration that drove the eventual failure.

The case was unprecedented: zinc-filled cable sockets had been used for more than a century, with no prior documented long-term zinc-creep failure. The report proposes, without establishing it as the cause, that low-level electrical effects from the telescope’s radio waves may have sped the zinc’s creep, and recommends making remaining cable and socket sections available for research. Its broader lesson is that custom-built scientific facilities can develop failure modes that past designs cannot predict. It calls for closer monitoring as such facilities age, explicit funding for ongoing maintenance, stronger inspection and operating procedures, and independent audits. The committee based its assessment on forensic studies, engineering records, photographs, repair proposals, research, and information from observatory staff.