Lokon-Empung is a double volcano located near the eastern tip of the northern arm of Sulawesi, Indonesia. It has two cone-shaped peaks, Lokon to the southwest and Empung 2.2 km to the northeast, with a saddle of volcanic rock separating the two. Of these Lokon is the larger, though it has not erupted in recorded history, whereas the slightly smaller Empung last erupted in the late eighteenth century. Situated on the saddle between the two summits is Tompaluan, a double crater that remains active to the current day.
Smoke rising from Tompaluan Crater. The Lokon summit is to the right, Empung to the left.
On 27 December 2011 the Pusat Vulkanologi Dan Mitigasi Becani Geologi (Indonesian Centre for Volcanology and Geological Hazard Mitigation) detected a series of seismic tremors beneath the mountain and imposed ban on traveling within 2.5 km of the crater. The following day the Jakarta Post reported a series of explosions from the crater.
Tompaluan is a very active volcano. In June-August 2011 a series of explosive eruptions and lava flows lead to over six thousand people being evacuated from around the mountain, with one fatality due to a heart attack during the evacuation process. Since then there have been smaller eruptions in October and November. There was also a small eruption in February this year. Prior to this year Tompaluan erupted in 2008, 2007, 2003, 2002, 2001, 2000, 1999, 1998, 1996, 1994, 1991, 1988, 1987, 1986, 1984, 1975, 1973, 1971, 1969, 1966, 1965, 1963, 1962, 196, 1958, 1951, 1949, 1942, 1930, 1893, and 1829. All eruptions prior to this appear to have been from the Empung crater.
The Lokon-Empung volcanic complex is located at the southern end of the Sangihe Volcanic arc, where an extension Molucca Sea Plate is being subducted beneath an extension of the Eurasian Plate, sometimes called the Sangihe Plate. As this happens part of the subducting plate is melted by the heat of the Earth's interior, and rises up through the overlying plate as liquid magma, forming volcanoes at the surface. 320(ish) km to the east the Molucca Plate is also being subducted beneath an extension of the Philippine Sea Plate, sometimes called the Halmahera Plate, producing a second chain of volcanoes in the Halmahera Islands. At some point in the future the Molucca Plate will vanish and the two volcanic arcs will meet.
The Molucca Sea, five million years ago (above) and today (bellow).