Page 391 - Caldera Volcanism Analysis, Modelling and Response

366 Thomas R. Walter

Troll et al., 2002). In this model, an intrusion of a radial dike outside a caldera ring-
fault is considered (Figure 9A). The radial dike is 15 km long and deep, and subject
to 1 m of uniform opening. This induces a displacement at the adjacent ring-fault.
Similar to the models described before, the ring-fault is allowed to open. The map-
view displacement vectors show extension perpendicular to the dike and two lobes
of uplift (Figure 9B), typical for shallow dike intrusions (Dzurisin, 2007). The side

Radial dike intrusion, opening at ring-fault

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

20 20
Radial dike intrusion 10 Opening 10
Opening
Opening
ring fault
ring fault
Uplift ring-fault
Uplift
Uplift
10 km 0 0
y Uplift
Uplift
Uplift
-10 -10
Opening
ring-fault
x -20 -20
-20 -10 0 10 20 -20 -10 0 10 20
C) Side views on opening ring-fault
z z
x y
0

Dike
Opening -10 Opening

Amount of
opening [m]
1
-4 0 4 -4 0 4
0
Figure 9 Radial dike intrusion causes opening of caldera ring-fault. (A) Model setup (x--y
plane). A radial dike with an area of 15 15 km is subject to 1m uniform opening.The dike is
located outside a ring-fault. Boundary conditions are set so that the ring-fault is allowed to
open. (B) A map view of horizontal displacement vectors at the surface (x--y plane) shows
displacement perpendicular to the dike, with two lobes of maximum uplift in the periphery.
U z displacement contours are locally in£uenced by the opening ring-fault. (C) Side views
shows opening of ring-fault (left shows x--z plane, right y--z plane) in the region facing the
radial dike.The zones of opening can be more easily intruded by ring-dikes, so a radial dike may
control the intrusion of an ensuing partial ring-dike.