Southern Patagonian Ice Field

An ice field in southern Chile and Argentina

The Southern Patagonian Ice Field (lang es), located at the Southern Patagonic Andes between Chile and Argentina, is the world's second largest contiguous extrapolar ice field. It is the bigger of two remnant parts of the Patagonian Ice Sheet, which covered all of southern Chile during the last glacial period, locally called the Llanquihue glaciation.

Thorough explorations include the expeditions of Federico Reichert (1913–1914), Alberto de Agostini (1931), and Harold William Tilman and Jorge Quinteros (1955–1956); as well as Eric Shipton (1960–61). The first (North South) crossing of the field was accomplished in 1998 by Pablo Besser, Mauricio Rojas, José Montt and Rodrigo Fica. Nevertheless, some areas of the field remain largely unexplored. From the air, initial exploration was conducted in 1928–29 by Gunther Plüschow after whom a glacier is named. From April 1944 to April 1945, the United States Army Air Forces conducted an aerial survey using the Trimetrogon method at the request of the Chilean government.

[[File:Mapa argentino de 1912 mostrando los hitos del límite histórico acordados por los peritos de Argentina y Chile en el Campo de Hielo Patagónico Sur. jpg|thumb|Argentine map of 1912 showing historical boundary markers agreed upon by the Argentine and Chilean experts, Fitz Roy, Huemul, Campana, Agassiz, Heim, Mayo and Stokes. The 1902 award considered that in that area the high peaks are water dividing and therefore there was no dispute. Both experts, Francisco Pascasio Moreno from Argentina and Diego Barros Arana from Chile agreed on the border between Mount Fitz Roy and Stokes. Since 1898, the demarcation of the border in the ice field, between the two mountains, was defined on the next mountains and their natural continuity: Fitz Roy, Torre, Huemul, Campana, Agassiz, Heim, Mayo and Stokes. In 1914 the Mariano Moreno range was visited by an expedition, however, Francisco Pascasio Moreno already knew of its existence. Argentina started to question the border arguing that the border should be in the Mariano Moreno range. In 1994, the Laguna del Desierto dispute was solved which involved territory of the Ice Field, an international tribunal awarded almost the whole zone to Argentina. After a refused appeal in 1995, Chile accepted the award. Since then, Chile has a small corridor to access Mount Fitz Roy and the Marconi Pass was defined as an international border crossing point. The Southern Patagonian Ice Field section of the border is the last remaining border issue between Chile and Argentina. On August 1, 1991, the governments of Chile and Argentina agreed on a borderline, but the agreement was never ratified by the Argentine legislature. Later, in 1998, both governments agreed to redraw the borderline between Mount Fitz Roy and Cerro Murallón

Section A (between Cerro Murallón and Daudet) and small part of B (from Fitz Roy to a point defined to the west) was drawn, however, they also agreed that section B (from Fitz Roy to Murallón) would wait until completion of a detailed 1:50,000 scale map of the area with further negotiations. To date, this one section remains the final non concluded boundary section and has been an irritant in Argentina Chile relations.

In February 2006, Ricardo Lagos appeared in a photo with the head of the Air Force, General Osvaldo Sarabia, in the undemarcated area, this caused controversy with Argentina. In 2006, the Argentine Instituto Geográfico Militar (IGM) (today Instituto Geográfico Nacional) edited a map without a note about the nondefined border but showed the Argentine claims as the official borderline. After Chilean diplomatic protests, the Argentine government withdrew the map and urged Chile to expedite the demarcation of the international border according to the 1998 agreement. On August 24, 2006, the Argentine Undersecretary of Tourism stated that the maps used by the Secretariat of Tourism's website were official because they were approved by the National Geographic Institute of Argentina. In 2006, president of Chile Michelle Bachelet and president of Argentina Néstor Kirchner held a meeting over the cartographic controversy. Kirchner served as the governor of the Santa Cruz Province from 1991 to 2003. In the maps published in Argentina, until today, the region continues to be shown without the white rectangle, as can be seen in a map of Santa Cruz on a website of an official Argentine agency. While in the official Chilean maps and most tourist maps, the rectangle is shown and it is clarified that the boundary is not demarcated according to the 1998 treaty. In 2018, Argentina made a National Ice Inventory in which are included some disputed glaciers. From September 20 to October 4 of the same year, the Argentine army traveled to into the area that is pending to be demarcated. This caused controversy mainly in Chile where the mayor of Villa O'Higgins denounced the fact as a "provocation" and made a call to the central government of Chile to reinforce the sovereignty in the zone. After the Argentine government published its inventory of glaciers including undefined territory the Chilean Foreign Ministry informed that a claim note had already been sent denying the Argentine inventory. In 2021, there was a controversy since CONAF (from Chile) installed a dome in the Circo de los Altares which its southern part is claimed by both countries. As of , the demarcation is still pending.