As our planet has evolved, major land forms have often been dependent on igneous activity. Features ranging from the mighty Andes, to the smallest hot spring are all dependent on the same processes of fire and earth that fuel and form the heat engines of our planet. One of these land forms that is common in the igneous environments is the feature known as a caldera.
Calderas are very important land forms, not only due to the importance of their ash flows in the geologic chronology and climate of the region but also due to their local control of the surface features. They also have interesting life cycles which are widely varied dependent on rock composition, tectonics and location. Lets now examine calderas: their formation, differences, and their locations on the planets surface.
Before the processes, and stages of caldera formation are described, the term caldera mustfirst be defined. A caldera is a more or less circular volcanic depression, which is presumably formed by the collapse of an underlying magma chamber. ( Hyndman p. 265) Calderas are further subdivided into two types, explosive and subdivide. (Summer field p. 118) The size of a caldera is variable, but it is generally larger than a volcanic crater, but smaller than a volcano-tectonic depression ( Stein berg p 267) Subsidence calderas are features that form subsequent to large eruptions that lower the level of magma in a chamber to the point that the chamber’s roof can no longer support itself and collapses. Explosive calderas are generally formed in association with large volcanic blasts and are essentially, larger versions of volcanic craters.
Another structure, closely related to calderas, is a calderon. This is a caldera like structure, with rectilinear of graben-like bounding fractures that are controlled by the regional tectonic framework. Calderas form in two environments. In epicontinental sialic rocks, and also in basaltic shield volcanoes.
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