At about 6.00 am local time, on the 2nd of July 2011, Mount Soputan, on the northern arm of Sulawesi Island in Indonesia began to erupt, for the first time since October 2008. The volcano produced a column of ash and smoke which initially reached 5 km in height, then grew slowly throughout the day, eventually reaching 14 km, before suddenly subsiding at about midnight. This ash-cloud was been drifting steadily westward covering several hundred km. It continues to produce isolated bursts of ash. The Indonesian government has ordered local people not to go within 8 km of the sight, though since the volcano is in a fairy remote location it is unlikely that anybody would do this anyway. It is unclear what the volcano will do in the near future, though it is unlikely to prove hazardous to human life. Soputan is a fairly active volcano, but has not caused any recorded fatalities, due to its remote location. It is possible that it might become a hazard to aviation.
Soputan Volcano, Northern Sulawesi.
Mount Soputan is a stratocone volcano (a classic cone shaped volcano of the sort you would expect to see in a Hollywood movie) which forms part of the Tondano Caldera, a 20 x 30 km complex of volcanoes fed from a single source. In addition to Soputan the caldera contains the Sempu, Lokon-Empung, and Mahawu stratovolcanoes, the Batu Kolok and Sarangson Hot Springs, the Tampusu Cindercone (a cindercone is a cone of ashes which forms downwind of a volcanic vent) and the Lahendong Maar (a volcanic crater caused by an explosion when lava comes into contact with groundwater).
Soputan is an active volcano, having most previously erupted in 2008, then before that in 2007, 2006, 2005, 2004, 2003, 2002, 2000, 1996 and so on. In 1906 a vent opened in the north-east flank of Soputan. This vent, given the name Aeseput periodically produced lava flows until 1924, but has been inactive since.
Of the other volcanoes in the caldera, Lokon-Empung is also fairly active, Mahawu last erupted in 1789 and there have been no recorded eruptions on Mount Sempu, which hosts a sulphur mine.
An eruption on Mount Soputan.
Suluwesi forms part of the Pacific Ring-of-Fire. It lies on the border between the Pacific, Eurasian and Australian plates. The Australian plate is moving northward, butting into the Eurasian plate, which is moving south-eastward. Eventually this collision, may turn what is now Indonesia into an extension of the Himalayas, with Australia attached to South-East Asia. This is made more complex by the Pacific plate moving eastward, being forced under the other two plates and subducted into the Earth's mantle. As this happens waterlogged sediments are melted by the heat of the Earth's interior and rise up through the overlying plates to form volcanoes. Sulewesi has 13 active volcanoes, and there are hundreds more scattered throughout Indonesia.
See also The Puyehue Eruption, Chile,