The process of Caldera Volcanoes like Lake Taupo is explained below.

Caldera formation generally follows the climax of major volcanic activity.
The formation and rise of a large body of magma to occupy a reservoir several kilometers below the earths surface starts the cycle.

A) Small portions of magma escape and reach the surface to form lava domes and flows, and pumice beds.

B) Catastrophic rapid eruption of ash and pumice may follow if the magma within the chamber begins to degas.

C) The shallow reservoir is then partially emptied by the eruptions withdrawing support from the roof of the reservoir.

D) Collapse of the roof of the reservoir causes the formation of the caldera.

E & F) Portions of the remaining magma still trapped beneath the caldera may them be erupted on the floor or along the walls of the caldera. The caldera may fill with water forming a lake and the new lava domes can typically form islands in the lake, like in Lake Taupo and Lake Rotorua.

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