News Navigator: How dangerous is the volcanic activity of Mount Shinmoe?
(Mainichi Japan) February 5, 2011
Mount Shinmoe, a 1,421-meter volcano in the Kirishima range, continues to erupt and make the news. The Mainichi answers questions readers may have about the volcano, known in Japanese as Shinmoedake.
.
Question: What kind of volcano is Mount Shinmoe?Answer: It is one of the most active of the nearly 20 volcanoes located in the Kirishima mountain range, which runs along the border of Kagoshima and Miyazaki prefectures. As recently as the summer of 2008, there was a small eruption at the volcano. It also appeared in a "James Bond" film, leading to headlines in overseas media like "Japan's 'James Bond' volcano erupts again."
.
Q: How do eruptions occur?
A: Magma, or molten rock, rises from deep within the earth, temporarily accumulates in a "magma chamber" located from a few to around 10 kilometers beneath the earth's surface, and when that chamber is full, the magma surges out.
Even if the magma does not come all the way to the top, its heat can boil underground water and create steam, the mounting pressure of which can lead to an explosion of steam out of the volcano.
.
Q: Does the current eruption look like it will continue for some time?
A: To answer that question, experts are looking at a past eruption of Mount Shinmoe: the Kyoho eruption, which started in 1716 and continued for a year and a half. At that time, heavy volcanic activity -- like that which started on Jan. 26 -- continued for three months. The volcano was then quiet for seven months, but after that it suddenly had a huge eruption. A pyroclastic flow -- a destructive mixture of ash, rock and volcanic gas that rapidly flows down a volcano -- destroyed homes and took lives.
Hints to whether the eruption this time will be long-lasting and whether it will develop into a large eruption like the Kyoho eruption can be found by examining the underground magma.
.
Q: How can you observe magma that is underground?
A; Researchers can't observe the magma directly, so they make inferences. For example, when magma rises, the volcano bulges very slightly, just enough to accommodate the volume of magma, and the slope of the volcano's side changes. Using tools such as global positioning systems, these changes can be observed down to the centimeter. Earthquakes caused by movements in underground magma or gas are another clue used by experts. Taking all of these factors into account, the Japan Meteorological Agency judges the danger of a volcano. It appears that a considerable amount of the magma in Mount Shinmoe's chamber may have been spent in the eruptions since Jan. 26.
.
Q: Does that mean the eruptions will end soon?
A: We hope so, but so far only around a tenth of the magma that was seen in the Kyoho eruption has been released. It's highly possible that new magma will enter the magma chamber. Furthermore, within the 700-meter-wide bowl-shaped crater of the volcano, lava has formed a large mound, acting as a lid on the magma below. Experts caution that if pressure from the magma passage below becomes too great, a large eruption could occur, taking the "lid" with it.
---
(Answers by Kosuke Hatta, Science & Environment News Department)
No comments:
Post a Comment