The 2015 eruption of Gamalama volcano (Ternate Island–Indonesia): precursor, crisis management, and community response

Abstract

Gamalama is an active stratovolcano on Ternate, a small volcanic island in Maluku Utara, Indonesia. Since 1510, a total of 77 eruptions have been recorded, with various impacts on the population and environment on the island and its surroundings. In July 2015, Gamalama erupted after < 24 h of precursor signs. The seismic activity continued to increase until September 2015, as marked by three sudden eruptions that were not preceded by significant volcanic and tremor earthquakes. This research was intended to understand the chronology and impact of the 2015 Gamalama eruption, which is categorically unusual, and to learn how the government conducted relevant crisis management and in what manners the community affected by ejected materials reacted to it. The former was achieved by analyzing the data provided by the Gamalama volcano observatory. As for the latter, interviews with key stakeholders in volcanic disaster management and a questionnaire-based survey involving 85 respondents in the most affected areas were conducted. The results showed that despite the relatively small Volcanic Explosivity Index (VEI = 2), the 2015 eruption was rather unexpected to many parties because it began with a short-term precursor sign (less than a day). The impact included tephra deposits as thick as 2–6 mm was in the Loto, Togafo, and Takome Villages. A total of 1791 people was recorded evacuating to several locations, such as Afe Taduma village, the SMKN 2 camp, the SKB camp, and the Naval Base camp. After a rapid impact assessment and coordination with the Center for Volcanology and Geological Hazard Mitigation (CVGHM), the government issued a status of emergency and evacuation orders. In cases when eruptions are initiated with a short-term precursor, the large population size and geographic condition of Ternate Island create a particular challenge in the resultant evacuation. Nevertheless, with prior mitigation measures and evacuation drills in hazard zones, evacuation can be carried out effectively. Even when a large-scale Gamalama eruption requires an evacuation to neighboring islands, a properly implemented mitigation such as the establishment of sister islands can substantially facilitate volcanic crisis management activities on small islands.