Page 363 - Caldera Volcanism Analysis, Modelling and Response

338 Agust Gudmundsson

magma reservoir with a width of 16 km and a height of 2 km, as in the circular
magma-chamber models. When the loading is doming, the deep-seated reservoir is
subject to magmatic excess pressure of 10 MPa.
In the first model, the chamber is located in a crustal segment subject to
horizontal tension of 5 MPa as the only loading. Here, the maximum tensile stress
s 3 and the Mises shear stress t peak at the appropriate locations for the initiation of
a ring fault (Figure 17). Since the stresses at the upper boundary of the chamber are

Figure 17 Sill-like magma chamber, 8 km wide and 2 km thick.The chamber is located at
3 km depth in a 20 km thick and 20 km wide layered crustal segment subject to horizontal
tensile stress of 5 MPa.The lower part of the segment (hosting the chamber) has a sti¡ness of
40 GPa, whereas the uppermost 3 km above the chamber consists of 30 layers alternating in
sti¡ness between 1and 100 GPa. (A) Con¢guration of the model; (B) contours of tensile stress
s 3 around the magma chamber; (C) maximum principal tensile stress s 3 and von Mises shear
stress s at the free surface; (D) contours of shear stress s around the magma chamber and (E)
tensile s 3 and shear s stress at the upper boundary of the magma chamber.