Not all mapping is about discovery…



Australian scientists 'undiscover' south Pacific island


A team of Australian and international scientists has 'undiscovered' a mysterious south Pacific island recorded on world maps for more than a decade.


Sandy Island has been shown on weather maps, Google Earth and in scientific publications going back to 2000 as sitting between the Australian mainland and the French island of New Caledonia in the eastern Coral Sea.


But when scientists on a research expedition aboard the RV Southern Surveyor sailed into the area last week, they were surprised to find nothing but empty ocean.


A team including Associate Professor Steven Micklethwaite, of University of Western Australia's (UWA) Centre for Exploration Targeting, was on a scientific excursion to collect submarine data and rock samples from the little-explored part of the Coral Sea. The expedition was aimed at understanding the tectonic evolution of the area.


The team became suspicious when the navigation charts used by the ship showed a depth of 1400m in an area where scientific maps and Google Earth showed the existence of a large island. They decided to investigate and found the charts were correct: the island shown by Google Earth as a black blob (at the coordinates 19˚14´S, 159˚56´E) simply did not exist.


"We all had a good laugh at Google as we sailed through the 'island'," said Associate Professor Micklethwaite. "Then we started compiling information about the seafloor, which we will send to the relevant authorities so we can change the world map."

He said nobody knew how the mistake had found its way into the databases used to produce maps.


"One of the sources of that map, ironically, is actually the CIA in the US so of course when we discovered this error we had lots of conspiracy theories floating around the ship. It certainly caused us to have a good giggle."


The excursion, which also included chief scientist Dr Maria Seton, of the University of Sydney, proved worthwhile in more ways than one: after 25 days at sea the team collected 197 different rock samples and more than 6,800 km of marine geophysical data, and mapped more than 14,000 square kilometres of the ocean floor.


Not only did they uncover rocks formed around 100 million years ago as Australia, Antarctica and New Zealand broke apart, but they also found extensive limestones at 3000m below the waves, revealing a massive drowning of the region over time.



Source :

Published on Tue, 27/11/2012





Sandy Island Mystery Solved 33 Years Ago



Free air anomaly detected by satellite altimetry



The above figure shows the free air anomaly detected by satellite altimetry (Sandwell and Smith model, V16.1, 2006). The presumed position of Sandy Island is represented by a black X and is located less than 15 km east of the main anomaly observed.



The ‘ghost island’, Sandy Island, is back in the spotlight today despite the fact that its mystery was definitively solved in 1979. During a recent survey of the tectonic evolution of the Coral Sea, the Australian research vessel Southern Surveyor found no land mass in the presumed position of Sandy Island.


The opposite would have been surprising, because in 1979, to put an end to the many doubts surrounding the existence of this island, Service Hydrographique et Océanographique de la Marine (SHOM) commissioned several aerial reconnaissance missions with a Maritime Patrol Aircraft (Neptune P2H) of the Naval Air Force in New Caledonia, which concluded that the island did not exist. It was deleted from nautical publications via a notice to mariners in March 1979.


The position in question is located in the French exclusive economic zone between the Chesterfield Islands and New Caledonia and France is responsible for international mapping of the area at the largest scale (1:1.5 million) (INT chart 636 and ENC (Electronic Navigation Chart) FR273210).


The official charts meet the objectives of navigational safety and are carefully developed and updated under strict conditions. This example demonstrates once again the importance of using reliable, official information provided by hydrographic services. These services actively inventory all available information in their areas of responsibility and transcribe the data on nautical documents after critical analysis. Likewise, in accordance with the provisions of the Convention on the Law of the Sea on marine scientific research in sovereign waters, the data collected by the Southern Surveyor will be forwarded to SHOM and used to update the nautical charts.


The Pacific Ocean is vast and much remains to be learned about its bathymetry. Although it is possible that undetected seamounts may reach the surface, it is highly unlikely that existing islands –especially ones allegedly as big as Sandy Island (25km) – would be omitted from official charts now that satellite imagery is available.


Sandy Island was reported by a whaling ship in 1876. This mistake may have arisen due to a positioning error (in the 19th century, positioning at sea was inaccurate and sometimes random, often with errors in longitude. The presumed position of Sandy Island is located just east of the Bampton reefs, which do actually exist.) Or it may have been due to a misidentification (although Sandy Island does not exist as an island, an underwater volcano does exist at this position and the presence on the surface of floating volcanic residue may in some cases suggest the existence of a land mass).


Because bathymetry is likely to remain incomplete for many years given the extent of the ocean to survey from hydrographic vessels, other techniques such as satellite altimetry are used to detect seamounts. However, though this technique can effectively detect the presence of large seamounts, it cannot accurately determine their depth, and if the seamount is likely to constitute a hazard to surface or submarine navigation, it is necessary to conduct a hydrographic survey of the area. In 2008, SHOM analysed the altimetry data of the area where Sandy Island was allegedly located. The free air anomaly of 80mGal observed in the data indicates a high probability of the presence of a seamount, and a seamount was indeed found by the Southern Surveyor. This underwater mountain already appeared on the charts at a depth of 1,474m. It will be more accurately described based on the data from the Southern Surveyor.



Service Hydrographique et Océanographique de la Marine (SHOM)