A full translation of a Kumanichi article analyzing the current state of Mt. Aso:
The eruption at Aso Nakadake No. 1 crater has continued over a half year increased activity. After the summer, “ash eruptions,” which emit magma as ash, have continued, and experts point out that this resembles the activities around 1989-90. Speculation that the magma has risen to about 2 km below surface, experts warn that “if movement towards a full-scale magma eruption continues, there is a possibility of an increase in the amount of ash fall over a prolonged period.”
On April 14, No. 1 crater was raised to alert level 2 due to the possibility of a small-scale eruption, restricting entry to 1 kilometer around the crater. Immediately after that, a very small eruption occurred for the first time in two and a half years. The hot water pool at the crator floor evaporated, and the amount of volcanic gas (sulfur dioxide) released per day increased. Volcanic tremor amplitude, which indicates the movement of underground gas and magma, has repeatedly increased and decreased since late July.
The magma chamber is said to lie 6 km underneath Kusasenri. However, professor Takahiro Okura from the Kyoto Volcano Research Center estimated from observations that the magma had risen horizontally to a depth about 2 km, creating a new magma chamber directly under Nakadake. Director Shinichiro Ikebe of the Aso Volcano Museum also sees that, since August, the volcanic ash contains much magma glass components and has already entered a form of magma eruption.
However, this state has stagnated for about 3 months. Prof. Okura pointed out that if the supply of magma increases and rises to near the crater in the future, there is a possibility of shifting to “Strombolian eruptions” that intermittently eject shards and splashes of magma. The temperature and crustal deformation near the surface of the crater is under observation, revealing magma transition.
“Ash eruption, which have lasted over 3 months, are similar to the activity around 1989-90. Considering the length of the run-up period, this may also be prolonged,” says Okura. During that time, magmatic eruptions continued intermittently for about 4 years, and there was a large amount of ashfall. Though possibility exits that activity will subside, ash countermeasures for machinery and crops as well as disemination of accurate information is necessary."
On the other hand, the restricted range when the last magma erupteion occured in 2014-15 was 1 km around the same crater. Prof. Okura says, “Even if a full-scale magma eruption occurs, it can still be dealt with within current limits."
The article contains an instructive graphic. I suggest you click on it. - Wiliam
