Hi–Brasil or Hy–Brasil is sometimes referred to as the Irish Atlantis and is a name given to a legendary island to the west of Ireland. It is frequently referred to as the Fortunate Island, which has obvious resonances with the Hesperides. Another appellation in Irish is Tir fo-Thuin or Land under the Wave. A further explanation offered for the origin of the name is that it is derived from an ancient term ‘brazil’that refers to the source of a rare dye, which is reminiscent of the expensive purple dye extracted from the Murex snail, traded by the Phoenicians.
One theory is that in the dim and distant past a part of what is now known as the Porcupine Bank, just west of Ireland, was exposed when the sea levels were lower as a result of the last Ice Age. When the feature was submerged by the rising seas it was probably eroded further by the ocean currents. The claim is that a memory of the exposed land lingered in the folk memory of the inhabitants of the west coast of Ireland.
The Genoese cartographer, Angellino de Dalorto (fl.1339), placed Hy-Brasil west of Ireland on a map as early as 1325. However, on some 15th century maps, the islands of the Azores appear as Isola de Brazil, or Insulla de Brazil. Apparently, it was not until as late as 1865 that Hy-Brasil was finally removed from official naval charts. Also found on medieval maps was another mystery island south of Brasil, sometimes appearing as Mayda, Asmaidas or Brazir(d).
Phantom islands have been shown on maps for hundreds of years and some as recently as the 20th century(f).
One of the most famous visits to Hy-Brasil was in 1674 by Captain John Nisbet of Killybegs, Co. Donegal, Ireland. He and his crew were in familiar waters west of Ireland, when a fog came up. As the fog lifted, the ship was dangerously close to rocks. While getting their bearings, the ship anchored in three fathoms of water, and four crew members rowed ashore to visit Hy-Brasil. They spent a day on the island and returned with silver and gold given to them by an old man who lived there. Upon the return of the crew to Ireland, a second ship set out under the command of Alexander Johnson. They, too, found the hospitable island of Hy-Brasil and returned to Ireland to confirm the tales of Captain Nisbet and crew.
The last documented sighting of Hy-Brasil was in 1872, when author T. J. Westropp and several companions saw the island appear and then vanish. This was Westropp’s third view of Hy-Brasil, but on this voyage he had brought his mother and some friends to verify its existence.
The Irish historian, W.G.Wood-Martin, also wrote[388.1.212] about Hi-Brazil over a hundred years ago.
Donald S. Johnson has also written an illustrated and more extensive account of the ‘history’ of Hi-Brazil in chapter six of his Phantom Islands of the Atlantic.
A modern twist on the story arose in connection with the Rendelsham UFO(b) mystery/hoax(c) of 1980, when co-ordinates that correspond to one of the Hy-Brasil locations was allegedly conveyed to one Sgt. Jim Penniston who kept it secret for thirty years(a)!
In 2010, the September 11th edition of the London Daily Mail (and its sister paper, the Irish Daily Mail) they ran an article with the adventurous headline of “The Atlantis of Connemara” that included the accounts of 20th century witnesses to unexplained visions off the west coast of Galway. Included was a potted history of recorded sightings since 1460.
In 2013 Barbara Freitag published a valuable in-depth study of Hy-Brasil dealing with its cartography, history and mythology.
Disappearing Islands, sometimes known as ‘phantom islands’ have been recorded in many parts of the world usually due to volcanic or seismic activity. However, there is now evidence that some of these phantom islands never actually existed(c). The most recent instance, in the Pacific, was reported on the BBC website(d) , where ‘Sandy Island’ which was shown on Google Maps was proven not to exist at all.
Examples of such islands are trotted out as some sort of proof of the type of event that caused the destruction of Atlantis. This suggestion does not stand up to the most cursory scrutiny. Firstly the examples adduced are usually small with short existences above water. The Atlantis portrayed by Plato is a large well-cultivated island with a large settled population. No island of that extent, longevity or development has ever been reported lost through seismic or volcanic forces. Even if one had, we should remember that the island described by Plato was only part of a larger empire of ten realms ruled by ten brothers.
Lists of these phantom islands are available on the Internet(a) while a more extensive study  of the phantom islands of the atlantic has been written by Donald Johnson(b).