Volcanoes surrounding Lake Taupo New Zealand
Caldera volcanoes surrounding Lake Taupo

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.

Small portions of magma escape and reach the surface to form lava domes.
Catastrophic rapid eruption may follow if the magma begins to de-gas
The shallow reservoir is then partially emptied by the eruptions withdrawing support from the roof of the reservoir.
Collapse of the roof of the reservoir causes the formation of the caldera.
Portions of the magma still trapped beneath the caldera may then 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 as in Lake Taupo and Lake Rotorua.