Lahendong is a geothermal field located in North Sulawesi, approximately 30 km to the south of Manado, the capital of North Sulawesi Province (Figure 1). Lahendong is the first geothermal area in Eastern Indonesia to generate electricity. As shown in Figure 1, there are two other potential geothermal areas to be developed beside Lahendong, namely Tompaso (Ganda dan Sunaryo, 1982; Prijanto et al., 1984) and Kotamobagu (Andan, 1982). The occurence of thermal activities in North Sulawesi (especially in the western part of Tondano lake) was recorded by A.R. Wallace. He is a British naturalist who visited Sulawesi in 1859 (Wallace, 1890 introduced by Whitten, 2008).
Geothermal areas in North Sulawesi lies on a complex tectonic setting. Lahendong is the only developed geothermal system in the world located in an arc – arc collision, where the Sangihe arc overrides the Halmahera arc (Hall, 2000; Figure 2). Geothermal systems in North Sulawesi are part of the Sangihe volcanic arc. Several Quartenary Volcanoes which are part of the Sangihe volcanic arc are depicted in Figure 1.
Figure 1. Location of the Lahendong geothermal system (1) and the Tompaso (2) and Kotamobagu (3) prospects with respect to major Quaternary volcanoes in North Sulawesi (compiled from Ganda and Sunaryo,1982; Prijanto et al., 1984; Andan, 1982; Morrice et al., 1983). Inset: Index map showing the position of the Lahendong geothermal system within the Indonesian Archipelago.
Figure 2. Major tectonic components of the north arm of Sulawesi and its surrounds. Lines with large barbs are subduction zones and lines with small barbs are thrusts (Macpherson et al., 2003). Quaternary volcanoes (filled triangles) along the Sangihe arc are from Morrice et al. (1983). Inset: W – E cross section of the Molucca Sea region showing the Sangihe arc overriding the Halmahera arc (Hall, 2000)
Lahendong geothermal field is situated about 10 km in to the west of Tondano Lake, a lake which occupies the structure referred to by Newhall and Dzurisin (1998) as the Tondano caldera (20 X 10 km2). Lokon and Soputan volcanoes are about 9 km northwest and 20 km southwest repectively, from Lahendong geothermal area (Lahendong). Lahendong geothermal system is hosted by andesitic and ryolitic rocks. The evidence of the occurence of thermal potential is identified by the active thermal manifestation in Lahendong village and its surrounding areas at about 750 m above sea level.
Lahendong geothermal area was first studied by Volcanological Survey of Indonesia (VSI) after the State Electricity Company (PLN) recognized the increasing demand for electricity in North Sulawesi (also known as Minahasa) and the difficulty of developing other local energy resources. From 1976 to 1978, PVMBG in collaboration with Japan International Cooperation Agency (JICA) had conducted several geological, geochemical and geophysical surveys.
These were followed by drilling three, narrow diameter (7.3 cm) holes about 350 m deep on the west side of Lake Linau in 1981 – 1982 (Prijanto et al., 1984; Suari et al., 1986). In 1980 Pertamina (the State Oil and Gas Enterprise) was appointed by the Government of Indonesia to develop the Lahendong prospect, with a generating target of 55 MWe. The development project began with detailed geoscientific exploration (Suari et al., 1987). Electricity production began in August 2001.
Until July 28th, 2016, 36 wells has been developed up to the depth of 1.500-2.500 m. Furthermore lahendong geothermal area has produced electricity with total capacty of 80 MWe. The steam production of lahendong geothermal area is managed by PT Pertamina Geothermal Energy (PGE), while the electricity generation is handled by PLN. Moreover, the direct use of gethermal brine has also been developed in the form of brown sugar production (collaborative project between PGE and Badan Energi Atom Indonesia/BATAN) from 2008.
Beside for electricity generation, geothermal areas can also serve as natural laboratory facility. Not only researchers from geology, geochemistry and geophysics, but also those who would like to study the diversity of animals and plants can observe the natural laboratory provided by geothermal area. Severals studies on geological and engineering aspects of geothermal have been conducted through UGM-NZAID programme Community Resilience and Economic Development (CaRED). The results of the study have been published in both national and international journals. The list below shows some publications about geothermal in North Sulawesi:
- Hydrothermal Alteration and Evolution of the Lahendong Geothermal System, North Sulawesi
- Initiating The Development Of The Lahendong Geothermal Education Park, North Sulawesi, Through Student Community Empowerment Program
- Lahendong Geothermal Education Park: a Proposed Geothermal Public Education Facility in the Eastern Part of Indonesia
- The Problem and Challenges to Development Lahendong Geothermal Education Park
- Distribution of Sr and Ca Isotopes in Fluids of Lahendong Geothermal Field
- Development Plan Of The Lahendong Geothermal Education Park, North Sulawesi
- Lahendong And Some Other Geothermal Systems In The Western Pacific Belt: Comparison On Their Geologic Settings, Hydrology And Hydrothermal Alteration
- Mass Transfer During Hydrothermal Alteration at the Lahendong Geothermal System, North Sulawesi
- Overview of the Lahendong Geothermal Field, North Sulawesi, Indonesia: a Progress Report
Interpretation of Well Logging Data on Lahendong Geothermal Field, Indonesia
- Tectonism and Volcanism Study in the Minahasa Compartment of the North Arm of Sulawesi Related to Lahendong Geothermal Field, Indonesia