Viedma () is a subglacial volcano whose existence is questionable. It is supposedly located below the ice of the Southern Patagonian Ice Field, an area disputed between Argentina and Chile. The 1988 eruption deposited ash and pumice on the ice field and produced a mudflow that reached Viedma Lake. The exact position of the edifice is unclear, both owing to the ice cover and because the candidate position, the "Viedma Nunatak", does not clearly appear to be of volcanic nature. Geography and geomorphology Viedma is located in the southern Patagonian Andes, southwest of Mount FitzRoy. The lake of the same name lies southwest of the volcano. The area is poorly accessible and the volcanic history poorly known. Viedma is part of the Austral Volcanic Zone. This volcanic zone consists of six volcanoes, from north to south Lautaro, Aguilera, Viedma, Reclus, Monte Burney and Fueguino. These volcanoes form a long chain of volcanoes, the most southern of which is a volcanic complex of lava domes and lava flows on Cook Island. Few things are known with certainty about the volcanic edifice of Viedma as it is mostly buried beneath glacial ice and the "Viedma Nunatak" was later revealed to not be a volcano. In 1956 Louis Lliboutry proposed that volcanic activity may occur in fissure vents buried beneath glaciers; between eruptions they would be concealed below the ice; Lliboutry considered dark bands on the ice to be tephra deposits, a view supported by a 1958-1959 expedition that found pumice on the Viedma Glacier. Other reports of volcanic phenomena in the region exist, and the existence of a large caldera beneath the Southern Patagonian Ice Field has been suggested as an explanation for volcanism there. Viedma Nunatak The Viedma Nunatak is commonly interpreted to be the site of the volcano, after observations made in 1944-1945 and 1950 by survey flights including controversial sightings of fumaroles which also led to the nunatak becoming known as the "Volcan Viedma"; but the lack of clear evidence and the difficulty of field sampling has rendered its identification with the Viedma vent contentious. The nunatak is about high above sea level. Most of the mountain is buried beneath the Viedma Glacier of the Southern Patagonian Ice Field and only parts of it crop out. The outcropping nunatak is elongated in north-south direction. A number of structures interpreted as craters and concave depressions are found especially on the