The geography of Indonesia is dominated by volcanoes that are formed due to subduction zones between the Eurasian plate and the Indo-Australian plate. Some of the volcanoes are notable for their eruptions, for instance, Krakatau for its global effects in 1883, Lake Toba for its supervolcanic eruption estimated to have occurred 74,000 Before Present which was responsible for six years of volcanic winter, and Mount Tambora for the most violent eruption in recorded history in 1815.
Peuet Sague is a volcanic complex in the northwest of Sumatra, Indonesia. The name peuet in Acehnese language means square in English. The location of the volcanic complex is isolated that needs several journeys on foot from the nearest village to reach the mountain. There are four summits in the complex that all of them are located in the Sigli Regency, Aceh Province. One of the lava dome is called Mount Tutung and it has 70 meters diameter and 80 meters deep of an active crater.
The first recorded eruption took place between 1918–1921. Due to its remoteness, the volcanic complex is infrequently visited. Little is known about its eruption history prior the 20th century.
In the morning of 26 April 1998, an ash eruption was spotted by a pilot of the Garuda Indonesia airline. The pilot saw the ash around three kilometer altitude when he flew over 7 km altitude. The local Indonesia Air Force chief confirmed the eruption from a fighter pilot who also spotted fire and thick smoke from the nearby forest. This was actually the second eruption from the first one on 19 April 1998, but the first eruption was obscured by a thick smoke from forest fires. Officials from the Ministry of Mines and Energy reported a phreatic eruption. The active crater was near Mount Tutung, 2 km west of the Peuet Sague's peak. Nobody was injured from this eruption because the nearest village is 8 km west of the mountain.
Between 9 March 1999 until 24 May 1999, volcanic activity in the Peuet Sague complex increased. Local people heard explosion noises about 20 times per day. Tectonic events increased and an eruption emitted white-gray ash up until 200 meters height. A white plume was observed between 10 0 20 meters height. All activities were then diminished.
The 1999's activity was later discovered to be continued until late of December 2000, although at a decreased level. The activity monitoring at that time was stopped due to a malfunctioning seismograph. Plumes continued to rise in June up to heights of 20 meters. Rumbling was heard on 18 occasions, and plumes continued to rise through 14 June 1999. A renewed activity began on 25 December 2000 with three explosions. Ash was spread over a relatively large area. Reports of ash-fall was occurred on Geumpang, Lutung, Mane and Bangke villages, up to 20 km away. A glowing lava flows at night was also reported. The 2000 eruption was estimated at scale 2 on Volcanic Explosivity Index.
