sedimentary rocks as well. Composition Viedma like other volcanoes of the Austral Volcanic Zone has erupted andesite and dacite. Phenocrysts include amphibole, biotite, hypersthene and plagioclase; orthoclase, plagioclase and pyroxene also occur as xenoliths. The rocks form a calcalkaline suite, but there is also an adakitic signature. The xenoliths may reflect a crustal contamination of the magma erupted at Viedma. Eruption history Tephra attributed to Viedma has been found in the Laguna Potrok Aike, including three tephra layers 26,991 - 29,416, 40,656 - 48,219 and 41,555 - 57,669 years before present which may originate either on Viedma or on Lautaro. Viedma has erupted during the Holocene; a tephra found in Lago Cardiel and dated 3,345 - 3,010 years before present may have originated at Viedma, although Aguilera and Lautaro are also candidate source volcanoes. Due to the absence of traces of volcanism at Viedma Nunatak the Global Volcanism Program removed its entry for Viedma in 2019. Historical Many observations referring to volcanic activity on the Southern Patagonian Ice Field exist, including reports of ashfalls, layers of tephra on glaciers and columns of smoke rising from the ice. A subglacial eruption occurred in 1988, depositing ash and pumice on the Viedma Glacier. These materials later gave rise to a lahar. The eruption had melted part of the ice and formed a network of valleys; it was assumed that it had taken place at some point between September and November of that year. Hazards There are no major population centres close to any volcano in the Austral Volcanic Zone, and the volcanoes are largely unmonitored. Among the know eruptions are large Holocene explosive eruptions, while historical eruptions took place in 1908 at Reclus and 1910 at Monte Burney. Future eruptions of volcanoes in the Austral Volcanic Zone may lead to ash fall at large distances from the volcano, including interruptions in air traffic and direct ash damage. See also Lautaro (volcano) Aguilera (volcano) List of volcanoes in Argentina List of subglacial volcanoes References Sources Subglacial volcanoes of Argentina Volcanoes of Magallanes Region Volcanoes of Santa Cruz Province, Argentina Andean Volcanic Belt Active volcanoes Mountains of Argentina Polygenetic volcanoes Quaternary volcanoes Quaternary South America