Page 282 - Caldera Volcanism Analysis, Modelling and Response

A Review on Collapse Caldera Modelling 257

Figure 11 Boundary-element results showing the contours of the maximum principal tensile stress
in megapascals. Models simulate a magma chamber subject to remote horizontal tensile stress of
5 MPa.Two chamber reservoir shapes have been considered: (A) spherical shape and (C) sill-like.The
other two sketches show the results of models emulating a magma chamber under the e¡ects of a
magmatic overpressure (10 MPa) in a reservoir located at the base (underplating) of the volcanic ¢eld
containing the magma chamber.Two di¡erent chamber reservoir shapes have been considered:
(B) spherical shape and (D) sill-like (modi¢ed after Gudmundsson,1998).

(3) Formation of ring faults considering regional extension or doming.
Elastic models indicate that sill-like chamber geometries subjected to
regional doming or extension may generate a stress field adequate for ring-fault
formation (Figure 11) even if the chamber overpressure is low (Gudmundsson,
1998; Gudmundsson et al., 1997) or inexistent (Gudmundsson, 2008). In the
case of doming, the area of the volcanic field subject to doming must, however,
be much larger than the cross-sectional area of the chamber, otherwise the
surface stresses peak above the centre of the chamber and do not favour the
initiation of a ring fault. Other geometries such as spherical magma chambers
are not suitable for ring-fault formation. Regional extension has also been
investigated by some time-dependent non-elastic models (e.g. Burov and