Sandy Island, New Caledonia

Sandy Island (sometimes labelled in French Île de Sable, and in Spanish Isla Arenosa) is a phantom island that was charted for over a century as being located near the French territory of New Caledonia between the Chesterfield Islands and Nereus Reef in the eastern Coral Sea. The island was included on many maps and nautical charts from as early as the late 19th century. It was removed from French hydrographic charts in 1974. The island gained wide media and public attention in November 2012 when the R/V Southern Surveyor, an Australian research ship, passed through the area and "undiscovered" it. The island was quickly removed from many maps and data sets, including those of the National Geographic Society and Google Maps.

History

On 14–15 September 1774, Captain James Cook charted a "Sandy I." snaking between latitudes 19° and 20°S and longitudes 163°50′ and 164°15′ E off the tip of New Caledonia. The associated map, titled "Chart of Discoveries made in the South Pacific Ocean...", was published in 1776. The depiction is part of the existing Grand Terre reef encasing New Caledonia, with coordinates of the area generally true to within 20 nautical miles (35 kilometres), despite Cook's use of dead reckoning. The whaling ship Velocity reported the fictitious island in the year 1876, as was noted on various late-19th-century maps, including an 1881 German map and 1895 British Admiralty chart. After returning from a voyage in the Pacific, the Velocity's master reported two unusual features. The first was a series of "heavy breakers", the second some "Sandy Islets", or Sandy Island. Both then appeared in an Australian maritime directory for 1879. It noted the islets extended north and south "along the meridian 159° 57' E" and "between lat 19° 7' S and 19° 20' S". Until the appearance of "Sandy I." in 1876–79, the nearest charted land or reef was the Chesterfield Islands 100 kilometres (55 nautical miles) westwards on the Bellona Plateau. At the time when the chart was created, it was standard practice for all potential navigation hazards to be listed on such charts as a precaution. Whether the fictitious Sandy Island was intended to be a correction to the position of Cook's islands of the same name is not clear. While at about the same latitudes, Cook's real "Sandy I." was four degrees of longitude—hundreds of miles—further east than the 160°E that became the usual location of the fictitious Sandy Island on later charts and maps that were drafted after the development of the marine chronometer and accurate longitude reckoning. Hydrographic charts later placed the internationally recognized abbreviation "ED" ("existence doubtful") next to Sandy Island, in recognition of subsequent failures to spot the reported island at the expected location. Seafloor mapping in the area by the Australian Hydrographic Service (AHS) determined a minimum depth for the immediate area around and over the island ranging from 1,488 to 2,353 metres (4,882 to 7,720 feet) below sea level. Due to a lack of appearance of an island or depths indicating a shallow reef, Sandy Island was removed from the official French hydrographic charts by the French Hydrographic Service in 1974 after a flying recognition campaign and by AHS in 1985. The information about the status of the phantom island was passed on to other national hydrographic services around the world, but Sandy Island remained in global coastline and bathymetry compilations used by the scientific community and was still there when the RV Southern Surveyor sailed toward the Coral Sea in October 2012. The erroneously reported island persisted because it was included in the World Vector Shoreline Database (WVS), a data set originally developed by the U.S. National Imagery and Mapping Agency (now the National Geospatial-Intelligence Agency, NGA) during the conversion from physical charts to digital formats, and now used as a standard global coastline data set. Inconsistencies in this data set exist in some of the least explored parts of Earth, due to human digitizing errors and errors in original maps from which the digitizing took place. One of the most commonly used derived products of WVS is the Global Self-consistent, Hierarchical, High-resolution Shoreline Geography Database (GSHHG), which is ported with Generic Mapping Tools (GMT) software. Although it is now an independent data set, an error in the original WVS data would have been present in this data set.

Pumice sea rafts The Velocity may have observed pumice sea rafts (masses of floating pumice ejected from an underwater volcano) traversing the Sandy Island area in 1876 and mistakenly recorded them as an island. This explanation is supported by a 2004 study of an eruption of a volcano near Tonga that found that pumice sea rafts associated with that eruption traveled more than 3,000 kilometers (1,900 mi) westward. An analysis of the pumice trajectory revealed that pumice rafts passed within 20 kilometers (12 mi) of the location of Sandy Island, approximately 200 days after the initial eruption. A study of coral migration from Tonga to the Great Barrier Reef found pumice rafts to be the mode of transportation, with a predicted path consistent with the 2004 study. Wind and ocean surface currents in the area may combine to funnel pumice rafts through the area between Fiji and New Caledonia on their way to Australia.

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