A pole of inaccessibility with respect to a geographical criterion of inaccessibility marks a location that is the most challenging to reach according to that criterion. Often it refers to the most distant point from the coastline, implying a maximum degree of continentality or oceanity. In these cases, a pole of inaccessibility can be defined as the center of the largest circle that can be drawn within an area of interest without encountering a coast. Where a coast is imprecisely defined, the pole will be similarly imprecise.
Northern pole of inaccessibility
The Northern pole of inaccessibility, sometimes known as the Arctic pole, is located on the Arctic Ocean pack ice at a distance farthest from any landmass. The original position was wrongly believed to lie at 84°3′N 174°51′W. It is not clear who first defined this point but it may have been Sir Hubert Wilkins, who wished to traverse the Arctic Ocean by aircraft, in 1927. He was finally successful in 1928. In 1968 Sir Wally Herbert came very close to reaching what was then considered to be the position by dogsled, but by his own account, "Across the Roof of the World", did not make it due to the flow of sea ice. In 1986, an expedition of Soviet polar scientists led by Dmitry Shparo claimed to reach the original position by foot during a polar night.
In 2005, explorer Jim McNeill asked scientists from The National Snow and Ice Data Center and Scott Polar Research Institute to re-establish the position using modern GPS and satellite technology. This was published as a paper in the Polar Record, Cambridge University Press in 2013. McNeill launched his own, unsuccessful, attempt to reach the new position in 2006, whilst measuring the depth of sea-ice for NASA. In 2010 he and his Ice Warrior team were thwarted again by the poor condition of the sea ice.
The new position lies at 85°48′N 176°9′W, 1,008 km (626 mi) from the three closest landmasses: It is 1,008 km from the nearest land, on Henrietta Island in the De Long Islands, at Arctic Cape on Severnaya Zemlya, and on Ellesmere Island. It is over 200 km from the originally accepted position. Due to constant motion of the pack ice, no permanent structure can exist at this pole. As of February 2021, McNeill said that, as far as he could ascertain, no one had reached the new position of the Northern Pole of Inaccessibility - certainly not from the last landfall across the surface of the ocean and it remains an important scientific transect.
Southern pole of inaccessibility
The southern pole of inaccessibility is the point on the Antarctic continent most distant from the Southern Ocean. A variety of coordinate locations have been given for this pole. The discrepancies are due to the question of whether the "coast" is measured to the grounding line or to the edges of ice shelves, the difficulty of determining the location of the "solid" coastline, the movement of ice sheets and improvements in the accuracy of survey data over the years, as well as possible topographical errors.
The pole of inaccessibility commonly refers to the site of the Soviet Union research station mentioned below, which was constructed at (though some sources give ). This lies from the South Pole, at an elevation of . Using different criteria, the Scott Polar Research Institute locates this pole at .
Using recent datasets and cross-confirmation between the adaptive gridding and B9-Hillclimbing methods discussed below, Rees et al. (2021) identify two poles of inaccessibility for Antarctica: an "outer" pole defined by the edge of Antarctica's floating ice shelves and an "inner" pole defined by the grounding lines of these sheets. They find the Outer pole to be at , from the ocean, and the Inner pole to be at , from the grounding lines.
The southern pole of inaccessibility is far more remote and difficult to reach than the geographic South Pole. On 14 December 1958, the 3rd Soviet Antarctic Expedition for International Geophysical Year research work, led by Yevgeny Tolstikov, established the temporary Pole of Inaccessibility Station (Polyus Nedostupnosti) at . A second Russian team returned there in 1967. Today, a building still remains at this location, marked by a bust of Vladimir Lenin that faces towards Moscow, and protected as a historical site.