Abstract
Caldera eruptions are among the most hazardous of natural phenomena.
Many calderas around the world are active and are characterised by
recurrent uplift and subsidence periods due to the dynamics of their
magma reservoirs. These periods of unrest are, in some cases, accompanied
by eruptions. At Campi Flegrei caldera (CFc), which is an area characterised
by very high volcanic risk, the recurrence of this behaviour has
stimulated the study of the rock rheology around the magma chamber,
in order to estimate the likelihood of an eruption. This study considers
different scenarios of shallow crustal behaviour, taking into account
the earlier models of CFc ground deformation and caldera eruptions,
and including recent geophysical investigations of the area. A semi-quantitative
evaluation of the different factors that lead to magma storage or
to its eruption (such as magma chamber size, wall-rock viscosity,
temperature, and regional tectonic strain rate) is reported here
for elastic and viscoelastic conditions. Considering the large magmatic
sources of the CFc ignimbrite eruptions (400-2,000 km3) and a wall-rock
viscosity between 10^18 and 10^20 Pa s, the conditions for eruptive
failure are difficult to attain. Smaller source dimensions (a few
cubic kilometres) promote the condition for fracture (eruption) rather
than for the flow of wall rock. We also analyse the influence of
the regional extensional stress regime on magma storage and eruptions,
and the thermal stress as a possible source of caldera uplift. The
present study also emphasises the difficulty of distinguishing eruption
and non-eruption scenarios at CFc, since an unambiguous model that
accounts for the rock rheology, magma-source dimensions and locations
and regional stress field influences is still lacking.
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