Thursday, January 16, 2014

Japanese Volcano Asosan Has Small Eruption [video]

The volcano known as Asosan, one of Japan's most active volcanoes, has had a small eruption amid a period of heightened unrest. Nestled in the center of a 14+ mile wide Pleistocene caldera, the resurgent stratovolcano has produced phreatic and magmatic eruptions periodically since its first historically recorded eruption in 553 A.D. On the 14th (after the GVP report), reported a magmatic eruption, and posted the below video.

The report from the Smithsonian GVP is as follows:

"On 27 December 2013 JMA raised the Alert Level for Aso to 2 (on a scale of 1-5) because volcanic tremor amplitude had been increasing since 20 December. However, on 2 January 2014 the amplitude rapidly decreased. Sulfur dioxide emissions were 1,200 tons per day during 2-9 January and 1,500 tons on 10 January. Volcanic tremor amplitude increased between 0800 and 1900 on 12 January. At 1215 on 13 January a very small eruption from Naka-dake Crater generated a grayish white plume that rose 600 m and drifted S, producing ashfall downwind."

The Smithsonain GVP describes Asosan:

"The 24-km-wide Aso caldera was formed during four major explosive eruptions from 300,000 to 90,000 years ago. These produced voluminous pyroclastic flows that covered much of Kyushu. The last of these, the Aso-4 eruption, produced more than 600 cu km of airfall tephra and pyroclastic-flow deposits. A group of 17 central cones was constructed in the middle of the caldera, one of which, Naka-dake, is one of Japan's most active volcanoes. It was the location of Japan's first documented historical eruption in 553 AD. The Naka-dake complex has remained active throughout the Holocene. Several other cones have been active during the Holocene, including the Kometsuka scoria cone as recently as about 210 AD. Historical eruptions have largely consisted of basaltic to basaltic-andesite ash emission with periodic strombolian and phreatomagmatic activity. The summit crater of Naka-dake is accessible by toll road and cable car, and is one of Kyushu's most popular tourist destinations."

Eruptions of volcanoes in Japan and its associated island chains are common. Near the end of 2013, the volcano Nishino-shima began a submarine eruption that became a new island volcano off its coast. That volcano is still erupting, and growing the new island, which will likely be permanent, much like the 1960's eruption of Surtsey in Iceland. The volcano of Sakurajjima is also frequently active, and has many webcams on the web that you can watch.

Japan lies on the Pacific Ring of Fire, and lies on a subduction zone which has been responsible for many volcanic eruptions, large earthquakes, and tsunamis. In 2011, a 9.0 subduction quake cause massive amounts of damage, and an associated tsunami which has sparked a nuclear disaster in Fukushima which is being compared to Russia's Chernobyl disaster (although still not as severe).

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