Page 279 - Caldera Volcanism Analysis, Modelling and Response

254 J. Martı ´ et al.

Figure 8 Example of the model geometry applied by Folch and Mart|¤ (2004). d, magma chamber
depth; he, magma chamber horizontal extent; ve, magma chamber vertical extent; a, fault dip
angle; DP, pressure di¡erence (modi¢ed after Folch and Mart|¤, 2004).

large plate-subsidence calderas, without the necessity for previous inflation–
deflation cycles. Here, low chamber underpressures would trigger collapse, yet
only a relatively small fraction of the magma chamber volume would be
extruded before the onset of collapse. In contrast, the formation of ring faults
for less eccentric geometries would be more complex, similar to that found
in analogue models, and probably dependent on the previous history of
deformation. This scenario would be associated with small to moderately sized
collapse calderas, commonly associated with the growth and destruction of large
stratovolcanoes and multiple episodes of chamber inflation and deflation. In this
scenario, a higher chamber decompression is necessary to induce the collapse,
implying the extrusion of a considerable fraction of the chamber volume before
the onset of collapse.
(2) Formation of ring faults considering overpressure load conditions.
Overpressure, combined with extensional load conditions, has been
investigated by several models assuming either elastic or non-elastic crustal
rheology (Table 1 and Figure 10). The advantage of time-dependent non-elastic