1831 CE mystery eruption - Zavaritskii caldera, Simushir Island (Kurils)

[Astronuc]

Cataclysmic 1831 Eruption Traced to Quadruple Volcano on Abandoned Soviet Island​

https://gizmodo.com/cataclysmic-183...volcano-on-abandoned-soviet-island-2000608193

In 1831, the Northern Hemisphere cooled by nearly 2 degrees Fahrenheit (nearly 1.1 degrees Celsius), throwing the climate into disarray and painting skies strange hues. Scientists long suspected a massive volcanic eruption was to blame, but its source remained unknown—until now. The recent study revealed that Zavaritski, Simushir’s relatively modest 2,047-foot (624-meter) volcano was the culprit. Ash from the eruption was later found in polar ice cores, solving the nearly 200-year-old mystery of which volcano triggered the global cooling.

The 1831 CE mystery eruption identified as Zavaritskii caldera, Simushir Island (Kurils)​

https://www.pnas.org/doi/10.1073/pnas.2416699122

Zavaritski Caldera
https://volcano.si.edu/volcano.cfm?vn=290180

https://en.wikipedia.org/wiki/Zavaritski_Caldera - the Zavaritsi Caldera (Russian: Вулкан Заварицкого, Vulkan Zavaritskogo), also spelled "Zavaritskii" and "Zavaritsky", is a caldera system located in the center of Simushir island, in the central Kuril Islands, Russia. The Zavaritski volcano contains three nested calderas, measuring 3 kilometres (2 miles), 8 km (5 mi) and 10 km (6 mi) in diameter.
https://en.wikipedia.org/wiki/Zavaritski_Caldera#1831_eruption

 

[SleipnirTheHorse]

Love volcanic stuff, do have any information on why a quadruple volcano would form and why it doesn't happen more often?