Lokon-Empung is a twin volcano lying on the rim of the Tondano Caldera in northern Sulawesi, Indonesia. In addition to Lokon-Empung, the volcanoes Mahawu, Sopotan and Sempu are located along the perimeter of the 20x30 km wide caldera which was formed by a massive eruption in the Late Miocene or Early Pliocene period. Nested within Tondano lies the more recent 3.5x5 km Pangolombian caldera and several subsequently formed volcanic edifices. The North Sulawesi-Sangihe Islands magmatic arc which encompasses the volcanoes around Tondano, including Lokon-Empung, is related to subduction of oceanic crust of the Molucca plate in a westward direction (thus sliding under Northern Sulawesi). The nearby Halmahera arc is associated with eastward subduction of the Molucca plate. The Molucca Sea Collision Zone is a presently unique example of the beginning of the orthogonal collision of two active subduction zones. The Molucca Sea plate lies between the two subduction systems and has been progressively subducted under the westward moving Halmahera Plate as well as the eastward moving Sangihe Plate, since about 7-17 and 25 million years ago, respectively. Whilst the subduction zones have yet to meet, the oceanic lithosphere of the Molucca Sea plate is no longer found at the surface but has been buried by about 20 km thick sedimentary formations being pushed infront of the two systems and referred to as the collision complex. Under this complex, the Molucca Plate is gradually sinking into the earths mantle. The Sangihe Plate is gradually starting to override the Halmahera forearc and eventually as the systems meet the Halmahera Plate will start to be subducted. The process is described in detail and related to the volcanic activity in the arcs in e.g. Clor et al. 2005 (Geochem. Geophys. Geosyst. 6(3), pp1-20), Elburg and Foden, 1998 (Earth Plan. Sci. Lett. 163, p.381-398), and MacPherson et al. 2003 (Geol. Soc. London, Special Publ. 219, p.207-220). The active crater of the Lokon-Empung complex, Kawah Tompaluan (1140m), lies on the saddle connecting Lokon and Empung volcanoes. No historical activity has been documented at Lokon (1579m), whilst moderate explosive eruptions occurred at Empung (1340m) around 1375 and 1775 (exact dates not known). Activity has since only been observed at Kawah Tompaluan. The first eruption at Tompaluan was recorded in 1829, with further eruptions in 1893-94, 1930, 1942, 1949, 1951-53, 1958-59, 1962-66, 1969-71, 1973-80, 1984, 1986-88, 1991-92, 2000-2003 and 2011-2012 (list last updated 2012). The 1991 eruptive phase produced particularly powerful eruptions. On 19. September, volcanic bombs falling in a radius of 500m of the crater set fire to nearby plantations. On 24-25 October significant ash emission occurred, sometimes associated with short pyroclastic flows. Up to one meter of ash fell around the crater and 2.5 cm in Kinilow, 4 km east of Tompaluan. About 10000 people were evacuated, particularly from Kinilow, about 3 square km of clove tree and coconut plantations were damaged, as well as nearly 1900 buildings (although presumably not badly). The eruption accounted for one fatality, a swiss volcanologist, who ventured too close to the crater on 24 October and was sadly killed by volcanic bombs before being buried in ash. Manado airport was closed due to volcanic ash for several days. The data in this text is largely derived from the Smithsonian GVP, as only few publications on Lokon exist. The documented activity was from 05.12-10.12, 2012. A week beforehand eruptions were occuring almost daily although activity was approximately at 3-day intervals at the time of the visit. Lokon-Empung volcanic complex lies in northern Sulawesi, about an hours drive from Manado airport. The volcano is best viewed from the resort town of Kinilow, which lies close to the city of Tomohon. The Highland Resort hotel offers a good view of the volcano and friendly staff. The crater zone is extremely hazardous during eruptive phases and is off limits to visitors. When activity is low, guides are available to take visitors on the about 1 hour climb to the crater rim. The KKVO Volcano Observatory on the outskirts of Kinilow. The observatory is responsible not only for Lokon-Empung and nearby Mahawu (see images below), but also for monitoring a number of other volcanoes in northern Sulawesi, including Soputan and several volcanoes on islands extending off the northern coast. The staff are friendly and will show interested visitors the monitoring equipment. Information panels showing the monitored volcanoes are also available.

• published: 03 Nov 2014
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