William Thank you to Kirk and KumaVista for that beautiful photo of Unzen seen across from Aso Kusasenri. A bit of poking about found that this string of volcanos is part of the Beppu-Shimabara graben, a rift which is widening at a rate of 1-2 centimeters per year. Rifts often result in volcanic activity; this rift also results in the numerous springs for which Kumamoto is world-renowned. Info is hard to find, but for us amateur geologists: https://twitter.com/VolcanoMagma/status/1274102236910481408/photo/1