Calderas

The calderas are volcanic depressions with a diameter superior than 1,5 km. There are several types: the Hawaiian calderas type, the subsidence calderas, and other less common as the resurgent calderas and caldera of "subsidence in cauldron".

The first are formed by coalescence of multiple collapsed structures, causing large rebates.

The formation of large subsidence calderas is associated with eruptions of plinian type, very violent and explosive, which are emited in large quantities of pyroclastic rocks in a short period of time. Subsidence occurs at the top of the volcanic edifice, along fractures, as a consequence of the quick emptying of the magma chamber which causes the mountain top miss bearing capacity and abates by large blocks.

Most of the Azores calderas formed by this process, as is the case of calderas of the Sete Cidades and Povoação (São Miguel Island), the Santa Bárbara (Terceira Island), or the Caldeirão (Corvo Island).