A radar analysis of Mount Asama, which has been showing activity since a medium-scale eruption Sept. 1, has confirmed there is magma at the bed of its crater, the Meteorological Agency and Geographical Survey Institute said Sunday.
The agency and the institute said the magma is the first observed at the volcano since 1973 and was caused by the Sept. 1 eruption. The volcano is located some 150 km northwest of Tokyo.
Radar images taken Thursday show a dome-shaped, layered form several dozen meters high with a radius of about 100 meters in the northeastern part of the crater.
It is believed the dome formed as a result of intermittent eruptions of magma and is 500,000 cu. meters in volume, the agency and the institute said.
“There have been no notable changes in volcanic activity and there is little likelihood of magma building up rapidly,” an agency official said.
But the official cautioned that an eruption similar in scale to the Sept. 1 event could still occur.
The Meteorological Agency also conducted infrared observation from above the volcano Saturday and confirmed that the temperature has risen to at least 150 degrees in a 50-meter area in the crater bed
The Sept. 1 medium-scale eruption was the first of that size since April 1983 at Mount Asama, which straddles Gunma and Nagano prefectures. It remained quiet until Tuesday when a small eruption occurred. Since then, countless small eruptions have been observed.
Thursday through Friday, volcanic ash, though a minute amount, was also observed in a vast area stretching to Tokyo and Chiba and Kanagawa prefectures.