Page 22 - Caldera Volcanism Analysis, Modelling and Response

Preface xxi

to infer causative sources. Troise et al. report on a new uplift episode at the
Campi Flegrei caldera after a prolonged period of overall ground subsidence. They
show that this new episode, which appears slower but longer than previous small
uplifts, sheds light both on the origin of small and large unrests, and on the
conditions to evolve towards large unrests. Evaluating an almost 25-year-long
record of geodetic observations, the authors propose that the maximum horizontal
to vertical displacement ratio can be a powerful indicator of source changes, and can
give important information for volcanic eruption forecast.
Todesco focuses on the role that hydrothermal systems may play in caldera
unrest. It is stressed that magma emplacement at depth as well as shallow circulating
hydrothermal fluids can generate geophysical signals measured at the ground
surface. Effective hazard evaluation requires a proper understanding of unrest
phenomena and correct interpretation of their causes. The author shows that
simultaneous modelling of different independent parameters is a powerful tool for
understanding caldera unrest. Her results highlight the importance
of comprehensive conceptual models that incorporate all the available geochemical
and geophysical information, and the need for high-quality, multi-parameter
monitoring and modelling of volcanic activity.
Echoing the need for cross-boundary multi-parameter investigations during
unrest episodes, Gottsmann and Battaglia present a review of recent advances of
gravimetric and ground deformation studies. They show that with deformation
data alone one cannot discriminate between magma and aqueous fluid intrusions,
but in combination with gravimetric data, the density of the intrusive fluids can be
assessed which helps in better constraining the nature of the causative source.
Through a series of case studies they highlight limitations of current standard
procedures, discuss different data inversion techniques and problems caused by
data aliasing and by the use of oversimplified models for the interpretation of
geophysical signals.
The final two papers explore the use of statistics for forecasting volcanic
phenomena. Tarraga et al. assess the failure forecast method (FFM) and its
applicability to the analysis of reawakening volcanoes and caldera unrest. Using an
automated FFM procedure, the authors present results from data collected during
the recent episode of unrest at the Las Can ˜adas caldera in Tenerife (Spain). The
authors note the importance of the long-term use of the FFM at a quiet or dormant
volcano as an essential prerequisite to define the baseline or normal behaviour of
the FFM, thus effectively reducing the number of potential false alarms during
reactivation.
Finally, Carniel et al. examine the memory or persistence of a given time series
collected at a volcano. They note that a time series that does not keep some
memory of its past cannot provide information about the future of an evolving
volcanic process, i.e. it cannot help to forecast an eruption. The authors report on
stochastic models developed for hazard estimation in the short-term by inspecting
time series sampled at Stromboli and Soufrie `re Hills volcanoes and in the long-term
using space-time data from the Osteifel and Tohoku volcanic regions. For the case
of the Las Can ˜adas caldera they show how the stochastic approach can provide
evidence for unrest.