Wednesday, January 16, 2013

Indonesia Volcano Seulawah Agam Rumbles, New Solfatara Forms

Indonesia is one place on the planet where active volcanoes are simply a part of life. With more volcanic activity than virtually any other place on the planet (at least above water), and more concurrent active volcanoes than any other nation, it typically doesn't make for great volcano blogging to mention the obvious, that some volcano in Indonesia with a hard-to-pronounce-name is erupting. But this week's Smithsonian GVP report caught my eye in regards to one Sumatran volcanoes rumblings.

Seulawah Agam volcano, one of the Northernmost volcanoes in the Indonesian archipelago has apparently begun to rumble. This volcano is of interest given that it has no 'confirmed' reports of historical eruptions, however this is uncertain. An eruption was reported int he 16th and 19th centuries, but no evidence has been found such as tephra layers, or any obvious lava flows that correspond to these dates. One theory posited by the GVP is that those mentioned eruptions could have been phreatic (water/steam driven) rather than magma related, which would make the eruptions very brief, and much less destructive.

However the nature of this volcano could change, as it is now becoming clear that magma is entering  the system. New solfataras (cracks that emit sulphurous gases and water vapor) have opened, and deformation is occuring. This means that if the volcano is going to erupt, it won't simply be a small phreatic eruption this time, and given the fact that we just don't know the last time it erupted, it could be a lot bigger than some of the normal eruptions in Indonesia.

More interesting still, it is located at the Northern tip of Sumatra, which has not experienced a whole heck of a lot of historical eruptions. It could be that the subduction of the plates underneath coupled with the recent spate of very large (7.0-9.1 magnitude) earthquakes has generated more fuel for the various magma chambers in the area.

Indonesia site on the Pacific Ring of Fire, which 'rings' the Pacific ocean with volcanoes. The bulk of these formed as a result of subduction, where one plate slides under another, creating magma through intense friction, heating of water at high pressure, and eventually creating a magma conduit to the surface. Most volcanoes that form on this subduction zone, like Seulawah Agam, are 'stratovolcanoes', which typically form into large, conical structures that look very much like our typical idea of a volcano.

This volcano, should it erupt (it is always possible that nothing will happen, as many magama intrustions do not result in an eruption at all!) has the potential to generate large explosions, heavy ashfall, pyroclastic flows, lahars, and other dangers to the surrounding population.

Here is the exact statement from the Smithsonian:

"SEULAWAH AGAM Sumatra (Indonesia) 5.448°N, 95.658°E; summit elev. 1810 m

CVGHM reported that visual observations of Seulawah Agam during 27 December-2 January seismicity increased. Visual observations were prevented due to fog, although on 2 January scientists observed a new solfatara that produced roaring noises and was within 20 m of van Heutsz Crater on the NNE flank. The Alert Level was raised to 2 (on a scale of 1-4) on 3 January. Geologic Summary.

Seulawah Agam at the NW tip of Sumatra is an extensively forested volcano of Pleistocene-Holocene age constructed within the large Pleistocene Lam Teuba caldera. A smaller 8 x 6 km caldera lies within Lam Teuba caldera. The summit contains a forested, 400-m-wide crater. The active van Heutsz crater, located at 650 m on the NNE flank of Suelawah Agam, is one of several areas containing active fumarole fields. Sapper (1927) and the Catalog of Active Volcanoes of the World (CAVW) reported an explosive eruption in the early 16th century, and the CAVW also listed an eruption from the van Heutsz crater in 1839. Rock et al. (1982) found no evidence for historical eruptions. However the Volcanological Survey of Indonesia noted that although no historical eruptions have occurred from the main cone, the reported NNE-flank explosive activity may have been hydrothermal and not have involved new magmatic activity."

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