According to the United States Geological Survey, the Indonesian region is one of the most seismically active zones on Earth. There are more than 120 active volcanoes in Indonesia and the country frequently experiences volcanic eruptions due to its location in the pacific ring of fire.
The ring of fire or the circum pacific belt is a path along the pacific Ocean characterised by active volcanoes and frequent earthquakes. Seventy-five per cent of volcanoes on Earth, i.e., more than 450 volcanoes, are found here. The region also witnesses ninety per cent of Earth’s earthquakes. The reason behind this is the movement of tectonic plates in the region as it lies near an intersection of shifty tectonic plates. These plates include the pacific, Juan de Fuca, Cocos, Indian-Austrialian, Nazca, North American, and Philippine plates. These plates overlap at convergent boundaries known as subduction zones along much of the ring of fire.
Recent Eruptions in Indonesia
Indonesia witnessed many volcanic eruptions in 2020. On December 01, 2020, an eruption on mount Semeru resulted in several villages around its slops getting engulfed under ash and sulphur. This resulted in emergency evacuation of thousands of inhabitants, who were advised to stay 4 km from the crater. The Indonesian authorities closely monitored several other volcanoes because sensors deteced increased activity.
Mount Sinabung was also closely monitored as sensors picked up increasing activity since August 2020. Villagers were advised to stay 5 kilometres away from the crater and remain vigilant.
Before this, Mount Ili Lewotolok, 12,060 feet (3,676 metres), released hot clouds raising as high as 13,100 feet (4,000 metres) into the sky, causing the evacuation over 4,600 people from the slopes of the mountain. Ili Lewotolok’s alert was raised to the second-highest level after sensors picked up increased activity. It had been rumbling since October 2017. Apart from that, authorities also evacuated more than 1,800 people from the volatile Mount Merapi volcano’s fertile slopes in November, 2020. Merapi spewed ash and hot gas as high as 6 kilometres (3.7 miles) into the sky in June 2020, but no casualties were reported. Its last major eruption in 2010 resulted in killing of 347 people and evacuation of 20,000 villagers.
According to a volcanologist from the Bandung Institute of Technology, Mirzam Abdurrahman, volcanic activity could increase relatively simultaneously in more than one mountain with the same triggers, as they are in the same Sunda Arc, which covers the islands of Sumatra, Java, Bali, West Nusa Tenggara, and East Nusa Tenggara.
Semeru is a stratovolcano, built up of alternate layers of lava and ash, located in East Java, Indonesia. Its common activity consists of ash plumes, pyroclastic flows, and avalanches, and lava-flows. The highest volcano on Java, it rises abruptly to 3,676 metres above coastal plains to the south. Summit topography is complicated by the shifting of craters from NW to SE. Frequent 19th and 20th century eruptions were dominated by small-to-moderate explosions from the summit crater, with occasional lava flows and larger explosive eruptions accompanied by pyroclastic flows that have reached the lower flanks of the volcano. It has been in almost continuous eruption since 1967.
The Sunda Arc is a volcanic arc, consisting of volcanoes that form the topographic spine of the islands of Sumatra, Nusa Tenggara, Java, the Sunda Strait, and the Lesser Sunda Islands. This Arc begins at Sumatra and ends at Flores, near the Banda Arc. It formed via the subduction of the Indo-Australian Plate beneath the Sunda and Burma plates at a velocity of 63-70 mm/year.