Geology of Mt. Fuji--an eruption on the way?

Friday, Sep. 7, 2012 Quakes added to eruption risk on Mount Fuji Kyodo Mount Fuji's magma chamber came under so much pressure from the Great East Japan Earthquake and one of its aftershocks last year that it could very well erupt, researchers said Thursday. However, the jump in pressure is not the only factor that could cause the volcano to blow, and no signs of a pending eruption have been detected, the National Research Institute for Earth Science and Disaster Prevention said. Mount Fuji most recently erupted in 1707 but under the same circumstances. At the time, the rise in pressure caused by the preceding quake, which hit right before the eruption, was weaker than that caused by last year's quakes, the group said. Based on the tectonic movements caused by the magnitude 9.0 quake that struck off the coast of the Tohoku region in March 2011 and the magnitude 6.4 quake that followed four days later, the researchers estimate that about 1.6 megapascals of pressure were placed on the magma chamber, which is thought to be some 15 km underground. That's equivalent to an atmospheric pressure of some 15.8 kg per sq. cm. In the past, 0.1 to several megapascals of pressure have been enough to trigger volcanic eruptions, including at Mount Fuji, it said. Although conditions in the magma chamber vary, 1.6 megapascals is "not a small figure," said Eisuke Fujita, a senior researcher at the institute.