The continuing eruption of Indonesia’s Mount Sinabung volcano has made headlines worldwide. Television pictures show refugees leaving their villages as the sequence of volcanic activity, which began on 15 September 2013, continues to intensify.
According to the country’s Institute of Disaster Management (Badan Nasional Penanggulagan Bancana, or BNPB) the current number of people displaced by the eruption stands at around 23,000.
Although the scale of the eruption is significant, and there is a need for humanitarian aid in the several temporary camps which are experiencing a shortage of necessities such as clean water and baby milk, the BNPB have announced that they do not classify the Mt. Sinabung eruption as a national disaster.
Mount Sinabung and Indonesia’s Volcanoes
Mount Sinabung, or Gunung Sinabung, is just one of many active volcanoes within Indonesia (the Smithsonian Institute’s Global Volcanism Program lists 145 within the country, of which 33 are located, like Sinabung, on the island of Sumatra). Sinabung is a stratovolcano (one made of alternating layers of ash and lava) and the current eruption is characterised by large numbers of debris flows of volcanic material known as pyroclastic flows (up to 426 of these were recorded in just two days on 4-5 January, 2014) and an ash plume rising to around 7km.
Unlike some other volcanoes, Sinabung does not have a long recorded eruptive history, although some earlier eruptions may have gone unrecorded. The only known eruptions are a probable but unconfirmed event in 1881, and an eruption which lasted for less than a month in 2010. By contrast, scientific and historical observations suggest that Java’s Raung volcano, which is also currently active, has erupted 66 times since 1586.
Indonesia is part of the so-called Pacific Ring of Fire, a belt of volcanoes surrounding the Pacific Ocean. The chain of volcanoes, especially along the islands of Java and Sumatra, is associated with plate movement. The subduction of the Indo-Australian plate beneath the Philippine plate, which is the cause of many destructive earthquakes, also generates volcanoes. As the crust is forced downwards, heat and pressure cause the descending rock to melt. Being more buoyant, it rises and reaches the surface, forming volcanoes.
Historic Volcanism in Indonesia
Although spectacular to see, and unquestionably devastating for many of those who live close by, the current eruption of Sinabung is by no means exceptional According to the monitoring website Volcano Discovery, five Indonesian volcanoes are currently classified as erupting, nine others are exhibiting minor activity and a further 16 are showing signs of unrest.
The dynamic geological and tectonic nature of Indonesia, and of the Java-Sumatra island arc in particular, needs very little illustration. In 1818 the volcano Tambora sprang into life with what’s thought to be the largest eruption during the Holocene period (the past 10,000 years); while the notorious Kratkatua eruption of 1883 produced a sound which was heard thousands of miles away.
On the Volcanic Explosivity Index these eruptions had ratings of 7 (super-colossal) and 6 (colossal) respectively – and such events are expected to occur once every thousand or hundred years. By contrast, the current eruption of Sinabung, which is rated as VEI 2, is merely ‘explosive’.
Volcanic Eruptions: Frequent and Devastating
Such eruptions occur on a weekly basis and the current event demonstrates that the impact of a volcano depends not just upon its size but upon the number of people who live close to it.
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