Page 385 - Caldera Volcanism Analysis, Modelling and Response

360 Thomas R. Walter

Deflating spherical magma reservoir enclosed by reactivated ring-fault

A) Map view, model setup B) Map view, displacement vectors

Magma chamber
(10 MPa 20
pressure drop)
10
X X'
Subsidence
0 Subsidence
Subsidence
-10
Freely slipping
ring-fault
-20
-20 -10 0 10 20 -20 -10 0 10 20

)
C) Cross-section, x-displacement (U x
0
X X'
-10

-20

D) Cross-section, z-displacement (U ) [in m]
z
0
X X' 1
Freely -10
slipping 0
ring-fault
-20 -1
-20 -10 0 10 20
Figure 4 De£ation of a spherical magma chamber enclosed by a ring-fault. (A) Model setup
(x--y plane). A ring-fault is de¢ned surrounding the magma chamber, with a radius of 10 km
at 2--20 km depth.The magma chamber is subject to a pressure drop of 10 MPa. As a result,
the ring-fault may be reactivated and slip in dip-slip and strike-slip. (B)--(D) Same as in
Figure 2. Displacement abruptly stops at the ring-fault, while U z deformation is ampli¢ed
inside the‘‘caldera.’’

3.2.1. Deflating spherical magma chamber
In this model, a deflating magma chamber is encircled by a ring-fault, which
reaches from the base of the magma chamber to the surface (Figure 5).
Displacement vectors and displacement contours suggest piston-type subsidence
with the largest horizontal displacement in the periphery (Figure 5B). The side
views onto the opening ring-dike (Figure 5C) show that the displacement at the
ring-fault is largest at depth near the magma chamber and is radially uniform,