Page 312 - Caldera Volcanism Analysis, Modelling and Response

Structural Development of Calderas 287

Figure 1 Surface structure of exceptionally exposed calderas: (a) n rim of Erta Ale caldera,
Afar, Ethiopia; (b) Wrim of Bromo caldera, Indonesia. Even in these favourable cases, it is still
not possible to de¢ne the deeper structure and how and why this developed.

central block is accommodated at crustal depths and (c) nature (geometry and
kinematics) of the caldera’s bounding faults.
This study tries to put constraints on the structure and development of calderas
through an overview of previously performed analogue experiments. Several sets of
analogue models have been performed, in the last years, to simulate calderas. These
have been run under different conditions, providing an invaluable amount of data to
understand the deeper structure and the development of calderas. Most of these
studies have focused mainly on the experimental results themselves, rather than on
the comparison to similar models and to nature; for this reason, these experiments
appear yet under-acknowledged within the volcanological community. Within this
framework, this study aims to: (a) give an overview of the experiments, highlighting
similarities and differences; (b) propose a consistent structural evolutionary model;
(c) reconcile this model with the available geological and geophysical data; and (d)
propose, from the comparison between models and nature, an updated genetic
caldera classification.

2. Analogue Modelling

2.1. General features
Analogue modelling consists of a scaled simulation of natural processes. Simulating
calderas, analogue models allow an understanding of the mechanism of collapse,
defining the mode of deformation and the role of the different parameters in
controlling the deformation. This is obtained through a systematic change in the
value of each parameter, while keeping the others fixed. This procedure allows
consideration of the general mechanism of deformation, potentially applicable to a
wide range of cases.
The main advantage of the analogue models is the possibility to directly observe
the deformation process in 3D, at an accessible laboratory scale (mm to m), within a
reasonable time span (minutes to days). Moreover, analogue models, conversely to