Mount Hudson

Mount Hudson
Cerro Hudson
Aerial photo from 1991
Highest point
Elevation	1,905 m (6,250 ft)
Coordinates	45°54′S 72°58′W / 45.900°S 72.967°W / -45.900; -72.967
Geography
Location	Chile
Parent range	Andes
Geology
Mountain type	Stratovolcano
Volcanic arc/belt	Southern Volcanic Zone
Last eruption	2011

Mount Hudson (locally known as Volcán Hudson) is a stratovolcano in southern Chile, and the site of one of the largest eruptions in the twentieth century. The mountain itself is covered by a glacier. There is a caldera at the summit from an ancient eruption; modern volcanic activity comes from inside the caldera. Mount Hudson is named after Francisco Hudson, a 19th-century Chilean Navy hydrographer.

Large eruptions around 4750 BCE and 1890 BCE are believed to have been of Volcanic explosivity index (VEI) 6; these are probably responsible for the large caldera. The 4750 BCE eruption may have wiped out many if not all groups of early man living in central Patagonia at that time, based on evidence from the Los Toldos archaeological site. Recently, the volcano has had moderate eruptions in 1891 and 1971 as well as a large eruption in 1991.

Before 1970, little was known about the mountain. Minor eruptive activity began in 1970 and melted parts of the glacier, raising river water levels and leading to the identification of the caldera. In August–September 1971, a moderate eruption (VEI 3) located in the northwest area of the caldera sent ash into the air and caused lahars from the melting of a large portion of the glacier. The lahars killed five people; many more were evacuated.

The eruption in August to October 1991 was a large plinian eruption with a VEI of 5, that ejected 4.3 km³ bulk volume (2.7 cubic km of dense rock equivalent material). Parts of the glacier melted and ran down the mountain as mud flows (see glacier run). Due to the remoteness of the area, no humans were killed but hundreds of people were evacuated from the vicinity. Ash fell on Chile and Argentina as well as in the South Atlantic Ocean and on the Falkland Islands. In 1992, John Locke Blake, then resident on Estancia Condor, south of Rio Gallegos in Argentina describes the effects of the eruption vividly. He describes an ash fall up to 15 cm in depth, covering some 150,000 to 180,000 square kilometres in a triangle from Los Antiguos to Deseado to San Julian to a depth of between 5 and 10 cm. He reports that the hygroscopicity of the silica caused the formation of morasses around drinking places causing sheep to be trapped and die in huge numbers. He records that 'ten years later, most of the farms in the affected area are empty, of sheep and of people'.