Indonesia’s most active volcano, Mount Merapi, increased its eruptive activity on 26 October 2010 (BBC news online “Indonesia volcano Merapi erupts, thousands evacuated”, 26 October 2010). The volcano is located on the island of Java and the eruption came the day after another in series of severe earthquakes centred on the region shook the island of Sumatra, also in Indonesia.
Mount Merapi: Some Facts
Mount Merapi is part of an active volcanic arc and is one of almost 150 volcanoes in Indonesia to be listed in the Smithsonian Institute’s Global Volcanism Programme, 41 of which are located on the island of Java. The volcano is a composite, or stratovolcano – namely, one formed of different layers of ash and lavas (Smithsonian Institute “Global Volcanism Program: Merapi” volcano.si.edu).
Although Merapi is currently heavily monitored, changes in its activity have been tracked in detail only since April 2006. During that time, the volcano has been almost constantly active with larger eruptions occurring. The Indahnesia website lists eleven separate alerts relating to its eruptive activity (Indahnesia “Changes in activity for Gunung Merapi” indahnesia.com).
Scientists first warned of an imminent eruption in the densely populated region on Monday 25th October and local people were warned to evacuate the area. Officials quoted on the BBC said that an estimated 13,000 people, some 5,000 of whom live on the slopes of the volcano itself, have been advised to move away.
Early reports indicate that some residents are reluctant to leave their homes and that several people have been injured by hot ash and at least one person killed (Sky News “Mount Merapi Begins To Erupt In Indonesia” news.sky.com). A previous eruption of the 2,968 metre peak, in 1930, is thought to have killed over 1,000 people (BBC).
Earthquake and Volcano Activity in Indonesia
Indonesia is located on a boundary between two of the earth’s tectonic plates. As a result it is highly seismically active and subject both to extensive volcanic activity and also to frequent major earthquakes. The day before the eruption, an earthquake of magnitude 7.7 shook the neighbouring Indonesian island of Sumatra ( United States Geological Survey, “Latest Earthquakes M5.0+ in the World - Past 7 days” earthquakes.usgs.gov).
Both earthquakes and volcanoes are the result of the descent of one of the earth’s tectonic plates below another. Volcanoes are caused by melting of rock under pressure as the earth’s crust is dragged downwards, while the earthquakes are the result of the stress built up as the two plates move past one another.
Although both natural hazards have the same root cause, there is no direct connection between them. The fact that such a major earthquake and a large volcanic eruption should occur within a day in the same country is coincidental. Given the nature of the region’s structural geology, however, such a coincidence is not altogether surprising.
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