Ehm why is this newsworthy? It was repeatedly shown to be nothing..
The quotes that it was a test were from journalists, and from people who "heard" about it. None from actual scientists who studied it.
> A December 2016 report by William Burr and Avner Cohen of George Washington University's National Security Archive and Nuclear Proliferation International History Project noted that the debate over the South Atlantic flash has shifted over the last few years, on the side of a man-made weapon test.[1] The National Security Archive briefing concluded:
>> A Central Intelligence Agency-sponsored panel of well-respected scientists concluded that a mysterious flash detected by a U.S. Vela satellite over the South Atlantic on the night of 22 September 1979 was likely a nuclear test.
> The newly released research and subsequent report was largely based upon recently declassified documents in files at the National Archives of Gerard C. Smith, a former Ambassador and special envoy on nuclear nonproliferation during Jimmy Carter's presidency.[1][60][5] Smith had once said: "I was never able to break free from the thought that the event was a joint operation between Israel and South Africa." The documents cited a June 1980 U.S. State Department report where Defense Intelligence Agency Vice Director Jack Varona had said the ensuing U.S. investigation was a "white wash, due to political considerations" based on "flimsy evidence". He added that the "weight of the evidence pointed towards a nuclear event" and cited hydroacoustic data analyzed by the Naval Research Laboratory. The data, he suggested, involved "signals ... unique to nuclear shots in a maritime environment" and emanating from the area of "shallow waters between Prince Edward and Marion Islands, south-east of South Africa".[1][5][60]
> In 2018, a new study made the case for the double flash being a nuclear test.[6][7][61][62]
The interesting fact is that there is very little speak of any other nation carrying out a nuclear test. It boiled down to Israel and South Africa, or a sensor glitch/weather fenomena. Kind of fun that the two nations vere the prime suspects although officially "nothing happened".
*Permanently uninhabited, but there's a research base there.
Atomic tests have routinely been carried out with scientific observers nearby, I mean, it's sorta the point of doing one. And as for people noticing, I would imagine apartheid South Africa had their own equivalent of an Official Secrets Act.
Also, the fact that the overwintering teams are all listed as ending their time there in September strongly correlates to the date of the Vela Incident. So entirely plausible to send the winter team home a few days early and delay the the summer team.
Prince Edward island is only 12 miles or so from Marion and visible from the base so it certainly did not happen in the waters between them.