Southern Patagonian Ice Field

The Southern Patagonian Ice Field (Campo de Hielo Patagónico Sur), 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.

Geography
The Southern Patagonia Ice Field extends from parallels 48° 15′ S to 51° 30′ S for approximately 350 km, and has an approximate area of 16,480 km2, of which 14,200 km2 belong to Chile and 2,600 km2 belong to Argentina.

The ice mass feeds dozens of glaciers in the area, among which are the Upsala (765 km2), Viedma (978 km2) and Perito Moreno (258 km2) in the Los Glaciares National Park in Argentina, and the Pío XI Glacier or Bruggen Glacier (1,265 km2, the largest in area and longest in the southern hemisphere outside of Antarctica), O'Higgins (820 km2), Grey (270 km2) and Tyndall (331 km2) in Chile. The glaciers going to the west flow into the fjords of the Patagonian channels of the Pacific Ocean; those going to the East flow into the Patagonian lakes Viedma and Argentino, and eventually, through the rivers de la Leona and Santa Cruz, to the Atlantic Ocean.

An important part of the ice field is protected under different national parks, such as the Bernardo O'Higgins and Torres del Paine in Chile, and the aforementioned Los Glaciares in Argentina.

There are two known volcanoes under the ice field; Lautaro and Viedma. Due to their inaccessibility they are among the least researched volcanoes in Chile and Argentina.

Circo de los Altares is an important hiking place.

Exploration
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.

Borderline


Although the boundary between Argentina and Chile in the area was established by the 1881 treaty and delimited in 1898 by the experts of both countries during the works of the experts of both countries for the 1902 award, in which they agreed they didn't have differences on that part of the border. The award is established "to perpetuity" by both countries under British tutelage. The map published by the British Crown, as part of the documentation of the 1902 award, illustrates a clear demarcation line (from the Fitz Roy to the Stokes) to the east of the Southern Patagonian Ice Fields leaving most of the territory in question in the Chilean side.

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.

Controversies after the 1998 Agreement
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 2024, the demarcation is still pending.