Mt. Aso Nakadake Crater

Nakadake is the active cone among the five peaks of Aso, inside a caldera that runs about 18 km east to west and 25 km north to south. Its crater is a line of vents about 1,100 metres long from north to south, and in recent years only the northernmost, the first crater, has been active. In quiet spells a hot crater lake called the yudamari fills the bottom. When the volcano stirs the lake dries up and the vent throws out black, sandy ash that locals call yona.

JMA raised Aso to alert level 2 on 21 June 2026 and to level 3 on 14 August, when volcanic tremor grew and sulphur dioxide output jumped. It lowered the level to 2 at 16:00 on 1 September after the tremor eased. The council reopened the road to Aso Sanjo Plaza at 9:00 on 2 September, and the ground within about 1 km of the crater stays closed. JMA's September report finds the volcano still in a heightened state, with high gas output, and warns of eruptions that reach about 1 km from the crater.

Here is what each level means on the ground. At level 1 only the inside of the crater is off limits, and the park road and crater rim open in good conditions. Level 2 closes the area within about 1 km of the first crater and the park road with it. Level 3 closes about 2 km, with the trails to Nakadake and Takadake, and can widen toward the inhabited areas about 4 km out. Levels 4 and 5 move people out of the homes most at risk.