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Many calderas are the culmination of long-lived volcanic systems. Field-based studies provide detailed descriptions and interpretations of the origins of individual examples, while analogue and mathematical modelling provide insights about caldera formation. Caldera morphology and structure yield information on subsidence mechanisms and geometry of the associated magma chamber, while studies of eruptive products address aspects of magma composition and eruption dynamics. Combining field data with analogue and numerical modelling leads us to propose a genetic classification of calderas based on the stress conditions that permit formation of ring faults and the pressure evolution in the magma chamber during a caldera-forming eruption. Two main end-members, referred to here as overpressure and underpressure calderas, develop from different initial conditions and generate different sequences of caldera-forming deposits. With overpressure calderas, stress conditions leading to the formation of ring faults are achieved prior to initiation of the eruption when an overpressurized sill-like magma chamber is loaded by mag-matic regional doming or subjected to regional extension. Caldera collapse is initiated near at the beginning of the eruption and the resulting eruptions are often very large. By comparison, underpressure calderas result from ring fault subsidence after significant decompression of the magma chamber following a pre-caldera eruptive episode.

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