Sciency Thoughts: Tangkubanparahu

Monday, 7 October 2013

Eruptions on Tangkubanparahu, West Java.

The Pusat Vulkanologi dan Mitigasi Bencana Geologi (Center for Volcanology and Geological Hazard Mitigation) has raised the alert level on Tangkubanparahu, a volcano 30 km to the north of Badung in West Java, following a string of small explosions that started at about 6.20 am local time on Saturday 5 October 2013 (about 11.20 pm on Friday 4 October, GMT). The volcano's crater is noted for its hot springs, which are a popular tourist attraction, and the explosions are thought to be phreatic in origin (caused by water percolating through rock and encountering hot rocks or magma then turning more-or-less instantly to steam, resulting in an explosion). The explosions were accompanied by the release of clouds of steam and gas, which reached 300 m above the volcano's summit. A 1.5 km exclusion zone has been set up around the crater as a precaution, as similar events in the past have been followed by toxic gas emissions and small ash plumes. Tangkubanparahu erupted in February this year, prior to which it had been quiet since 1983.

A cloud of white steam above Tangkubanparahu at about 6.50 pm local time on Saturday 5 October 2013. Mega Nugraha/Tribun News.

The Indo-Australian Plate, which underlies the Indian Ocean to the south of Java, is being subducted beneath the Sunda Plate, a breakaway part of the Eurasian Plate which underlies Java and neighboring Sumatra, along the Sunda Trench, passing under Java, where friction between the two plates can cause Earthquakes. As the Indo-Australian Plate sinks further into the Earth it is partially melted and some of the melted material rises through the overlying Sunda Plate as magma, fueling the volcanoes of Java and Sumatra.

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Saturday, 1 September 2012

Seismic activity beneath Mount Tangkubanparahu.

Mount Tangkubanparahu is a shield-like stratovolcano (cone-shaped volcano, with a low, broad profile) located on West Java to the north of Bandung, the former capitol of Indonesia. It is located on the western rim of the 6 × 8 km Sunda Caldera, the remains of a supervolcano thought to have been active 190 000 years ago. Tangkubanparahu itself rises to a height of 2084 m, and has undergone a number of small eruptions since the nineteenth century, though no major eruption has ever been observed; an eruption in May 1846 did cause some fatalities due to lahars (mudflows) and possibly small pyroclastic flows (avalanches of hot ash and gas). The last major eruption on Mount Tangkubanparahu is thought to have happened about 9500 years ago.

Satellite image of Mount Tangkubanparahu. Google Maps.

Between 13 and 23 August 2012 the Pusat Vulkanologi dan Mitigasi Bencana Geologi recorded an increase in seismic activity (small Earthquakes) beneath Tangkubanparahu, and visitors to the crater were banned as a precaution. Earthquakes beneath volcanoes can be a sign of magma moving in chambers under the visible cone, which can be a precursor to an eruption, although Tangkubanparahu has undergone at least four periods of raised seismicity since the last eruption, a small crater explosion in 1985. However this does not imply the tremors are completely safe; seismic activity on Tangkunbanparahu is often associated with fumaroles (gas emissions) which are typically high in toxic sulphur dioxide (SO₂). In September 2002 a number of dead animals were found near the summit after a series of minor tremors.

Java is located on the southern margin of the Sunda Plate. To the south of the island the Australian Plate is being subducted beneath this plate in the Sunda Trench, passing under the island and sinking into the Earth. As the plate is subducted it is partially melted by the friction and the heat of the planet's interior. Some of the melted material then rises through the overlying Sunda Plate, fueling the volcanoes of Java and neighboring Sumatra.