The subduction process is related to the production of volcanoes in Japan as the downgoing oceanic slab undergoes dehydration at depths of roughly 90 to 100 km beneath the overriding plate.

[13] Water in the structure of hydrated minerals interact with the upper mantle, lowering its melting point.

As the mantle begins to melt, its density decreases and rises through the upper crust, forming a volcanic vent.

The climactic eruption began on 4 August and lasted for 15 hours,[17] and contained pumice falls and pyroclastic flows.

[23] The effects of this eruption were made worse because, after years of near or actual famine, neither the authorities nor the people had any remaining reserves.