Thompson Island (South Atlantic) — a phantom island and its history

Early reports and descriptions

The origin of the Thompson Island story dates to the voyages that followed the discovery and rediscovery of remote subantarctic islands. Bouvet Island itself was first sighted in the 18th century and was re-sighted several times during the 19th century. During one of those voyages, between 13 and 16 December 1825, Captain George Norris of the Sprightly recorded a small island northeast of Bouvet and described turbulent seas around it. He named the land Thompson Island and identified three nearby rocks he called the "chimneys" because of their shape. Norris sketched positions and included these features in his log, though later analysts noted discrepancies between the coordinates in his map and those in his written notes.

Subsequent sightings, mapping and doubts

Reports that may have referred to Thompson Island resurfaced in later years. An 1853 British Admiralty chart showed Thompson Island together with Bouvet and the Chimneys, giving the impression of formal acknowledgement. In 1893 Captain Joseph J. Fuller reported sighting Thompson Island while commanding the Francis Allyn, and some chartmakers continued to include it. At the end of the 19th century the German Valdivia expedition sought to clarify positions in that region but did not verify the island. The scientific vessel Meteor later measured a sea depth of 1,579 m near the coordinates where Thompson had been reported (1915), and a Norwegian expedition in 1928–29 explicitly searched for the island and reported no evidence of land at the claimed location, concluding that it did not exist.

Possible explanations

Several hypotheses have been proposed to explain how Thompson Island entered the charts and why it disappeared from them:

• Misidentification: an iceberg, an atmospheric mirage, or a distant view of Bouvet Island itself could have been mistaken for a separate islet.
• Navigation and charting errors: 19th‑century position fixing at high latitudes was difficult, and transcription mistakes could have created phantom features by shifting coordinates.
• Volcanic emergence and subsidence: Bouvet and nearby seafloor have volcanic origins, and a transient volcanic cone might theoretically have risen and later collapsed or been eroded away. Some commentators have suggested a volcanic eruption in the late 19th century as a possible cause, but there is no direct evidence that a volcanic island appeared and then vanished at the reported spot.

Cartographic legacy and significance

Thompson Island is an example of cartographic inertia: once a feature appears on authoritative charts, it can persist for decades despite later negative evidence. Thompson continued to turn up on some maps until at least the mid‑20th century, even as hydrographic surveys tightened standards. The case illustrates the challenges of early polar and subantarctic navigation, the limits of visual observation in high latitudes, and the evolution of charting practices from reports and sketches to systematic surveys with soundings and later sonar.

What is generally accepted today

Contemporary nautical charts do not show Thompson Island. The most likely conclusion among historians and hydrographers is that the island was either a mistaken sighting—possibly of Bouvet Island or of pack ice—or a transient feature that left no lasting trace. The only near‑contemporary detailed description comes from Norris, and later descriptions such as Fuller's have been judged inconclusive or possibly conflated with Bouvet. Thompson survives mainly as a historical curiosity and a cautionary example about early seafaring reports and the persistence of phantom islands on maps.

Timeline (key entries)

1. 1739 — Initial European discovery of Bouvet Island (context for regional exploration).
2. 1825 — Captain George Norris records Thompson Island and nearby "chimneys."
3. 1853 — Features appear on an Admiralty chart, giving them official visibility.
4. 1893 — Captain Joseph J. Fuller reports a sighting; some charts retain the feature.
5. 1898 — The Valdivia expedition attempts but fails to locate Thompson.
6. 1915 — The Meteor records a deep sounding near the reported position.
7. 1928–29 — A Norwegian expedition fails to find Thompson and declares it nonexistent.
8. Mid‑20th century — Thompson ceases to appear on modern nautical charts.