Collapse calderas are defined as the volcanic depressions that result from the disruption of the magma chamber roof due to down faulting during the course of an eruption. The diameter of these volcanic depressions, usually more or less circular or elliptical in form, are many times greater than the diameter of the eruptive vents (Lipman, 1997, 2000). Despite their low frequency of occurrence, large pyroclastic eruptions and associated caldera collapse structures represent one of the most catastrophic geologic events that have occurred on the Earth’s surface during Phanerozoic times, causing considerable impacts on the environment (e.g. climate) and on human society (e.g. Tambora, 1815 (Self et al., 1984; Newhall and Dzurisin, 1988), Krakatau, 1883 (Self and Rampino, 1981; Simkin and Fiske, 1983; Newhall and Dzurisin, 1988) and Pinatubo, 1991 (Hattori, 1993; Lipman, 2000; Dartevelle et al., 2002)). Additionally, collapse calderas have received considerable attention due to their link to ore deposits and geothermal energy resources (Lipman, 2000).
Calderas have been analysed through field studies, analogue models and numerical simulations (e.g. Druitt and Sparks, 1984; Komuro et al., 1984; Martí et al., 1994; Bower and Woods, 1997; Gudmundsson et al., 1997; Gudmundsson, 1998; Burov and Guillou-Frottier et al., 1999; Acocella et al., 2000, 2001, 2004; Guillou-Frottier et al., 2000; Martí et al., 2000; Roche et al., 2000; Roche and Druitt, 2001; Folch and Martí, 2004; Gray and Monaghan, 2004; Lavallée et al., 2004; Geyer et al., 2007). However, some important aspects on caldera dynamics and structure still remain uncertain and controversial.
Traditionally, field studies have constituted the most important way to investigate and understand volcanic processes. Structural, stratigraphic, sedimentological, petrological and geochemical investigations have been necessary to understand processes from magma generation to volcanic eruption. In the case of caldera-forming eruptions, field studies have provided also valuable information concerning the caldera-forming deposits and the related collapse structures. The reconstruction of past collapse calderas and their comparison with historical examples (e.g. Fernandina, Galapagos , Chadwick and Howard, 1991 ; Katmai, Alaska , Hildreth and Fierstein, 2000; Hildreth et al., 2003; Miyakejima, Japan , Geshi et al., 2002; Nakada et al., 2005) is a powerful tool to understand caldera mechanisms.
There exist a large number of scientific papers compiling field data from hundreds of collapse calderas distributed worldwide (e.g. Steven and Lipman, 1976; Aramaki, 1984; Rytuba and McKee, 1984; Eyal and Peltz, 1994; Geshi et al., 2002). Although dealing with such a large amount of information from original sources is usually unfeasible, easier-to-use databases compiling the existing information on field studies of collapse calderas are scarce and incompleteThe Smithsonian National Museum of Natural History (http://www.volcano.si.edu/) offers a database of those volcanoes active during the last 10,000 years including caldera-forming events. The information recorded in this database includes a detailed description of the caldera geographical location (e.g. world region, subregion, latitude, longitude, elevation), the volcano number according to the Catalogue of Active Volcanoes of the World (CAVW), a brief description of the geological history and a photograph. Newhall and Dzurisin (1988) compiled worldwide historical unrest at large calderas. In their database, the authors incorporate jointly with the abovementioned information a short description of the associated tectonic setting, the type of pre-caldera edifice and the historical unrest. Other smaller compilations like those of Spera and Crisp (1981) and Walker (1984) provide additional information regarding caldera areas and volumes of extruded deposits, and the distribution of post-caldera vents, respectively.