Page 19 - Caldera Volcanism Analysis, Modelling and Response

xviii Preface

let alone with a caldera-forming event. The general idea that all unrest is triggered
by the arrival of new magma at shallow depth is also eroded by the fact that
few historic unrest periods culminated in eruptions and by the increasing evidence
for a significant role of shallow hydrothermal fluid migration during unrest
(Bonafede and Mazzanti, 1998; Battaglia et al., 2006; Gottsmann et al., 2007).
With the aim to sample state-of-the-art of caldera studies and to contribute to
the understanding of collapse calderas and their processes, we organised an
international workshop entitled Caldera Volcanism: Analysis, Modelling and
Response, in Tenerife, Canary Islands, in October 2005. More than 40 dedicated
scientists, covering a wide range of disciplines (structural geology, melt physics,
geophysical monitoring, stratigraphy, numerical modelling and gas monitoring,
to list just a few), attended the workshop and presented the most recent results
from their studies. One of the most interesting results emerging from the passionate
and down-to-the-nitty-gritty scientific discussions during that workshop was the
general acknowledgment of the desperate need for a joint multi-disciplinary cross-
boundary collaboration to tackle the many outstanding and unresolved issues on
the formation and the behaviour of collapse calderas. We need to put together
geologists, physicists, modellers, geophysicists, geochemists, mathematicians and
others in order to fully comprehend caldera dynamics, their potential effects on our
environment in general, their associated hazards and their economic benefits in
order to give informed advise to decision makers for risk mitigation.
The idea of locking up a bunch of scientist in a remote mountain resort for one
week with not much more to do except talk science (and astonishingly devour
the hotel’s bar of any liquid carbonhydrates) proved the right concept. Several
major questions were raised during the workshop, testing to the bone our current
knowledge on collapse calderas. Some of these questions were:
How do collapse calderas form? What are the conditions to create fractures and
slip along them to initiate caldera-collapse and when are these conditions fulfilled?
How do these conditions relate to explosive volcanism?
Does extensional tectonism drive caldera volcanism or vice versa?
Most products of large caldera-forming eruptions show evidence for pre-eruptive
reheating. Is this a pre-requisite to produce large volume eruptions and large
calderas?
What is the time-scale of caldera processes? How long does it take for magma to
reach conditions ripe enough to generate a caldera-forming eruption?
Do magma chamber walls behave elastically, viscoelastically or rigidly during
caldera-collapse?
Do calderas form by underpressure following a certain level of magma chamber
withdrawal during a previous eruptive episode or by magma chamber loading
due to deep doming (underplating), or both?
How to generate underpressure in a magma chamber?
How can we interpret unrest signals in active caldera systems? What is the origin
of seismic tremor?
Which criteria could be used to differentiate between pit craters and collapse
calderas?