The different types of volcanoes on Earth have been presented in the previous chapters. Volcanic edifices are all created by the accumulation, or ‘aggradation’ of eruptive products (cf. Cas and Wright in Volcanic Successions: Modern and Ancient. Springer, Dordrecht, Netherland, pp 362–410, 1988), although the duration of the eruption and the time between periods of activity can vary widely. During inactive periods, volcanoesAltiplano–Puna Miocene/Pliocene volcanoes tend to undergo ‘degradation’, but this may also occur even during active periods. Newton’s aphorism about gravity, “what goes up, must come down”, can also be applied to volcanoes (e.g. Fink in Nature 359:102–103, 1992) in the sense that what is built up by eruptions is subsequently removed by degradation, involving various erosional processes.