This is why you don’t build your tourist center closer to the center of a world champion of explosive eruptions:
The flows only ran out 1 km. No one was injured, fortunately.
Mount Aso is a big caldera (see image at top of page; the big valley is the caldera, Nakadake is part of that central peak complex, I think). It last blew 90,000 years ago and now has several much smaller active vents (Nakadake was the eruption vent this time).
As far as I can tell, Asosan is still at Level 3 out of 5 alert, but there have been no more blasts since that one in October.
Volcanologists I follow tweeted about this eruption’s classic pyroclastic flows and block-and-ash flows, so here are a couple of short informative videos on these phenomena.
Follow-up, November 28, 2021: Per this week’s Global Volcanism Program report:
JMA lowered the Alert Level for Asosan to 2 (on a scale of 1-5) at 1100 on 18 November and decreased the restricted area to a radius of 1 km, noting that no eruptions had been recorded since the 21 October eruption. The sulfur dioxide emission rate remained elevated in November and was 2,100 tons per day on 16 November. The amplitudes of volcanic microtremors fluctuated for a period after the eruption, though they were generally small beginning on 1 November.
Featured image: Aso Caldera, by 555hot8p 10/Shutterstock