Page 16 - Caldera Volcanism Analysis, Modelling and Response

PREFACE

Caldera-forming eruptions are among the most awe-inspiring and powerful displays
of nature’s force, yet at the same time they constitute a major natural hazard. An
eruption on this scale can wreak large-scale havoc, claim significant losses in lives
and assets and can significantly impact regional and global climate and living
conditions. Calderas are undoubtedly enigmatic displays of Earth’s evolution and
often display the most scenic landscapes on this planet, attracting millions of visitors
each year. Despite their potential ferocious nature, calderas play a crucial role in
modern society’s life. Calderas host essential economic deposits and supply power
for many via the exploitation of geothermal reservoirs and thus receive considerable
scientific, economic and industrial attention. Yet, they also pose a serious threat
to our livelihood in case of their reactivation as they can significantly impact
our environment both locally and globally (Lipman, 1997, 2000). Volcanic hazards
associated with collapse calderas differ markedly in space and time from hazards
associated with solitary volcanoes. Probably one of the most remarkable hazards related
to caldera-forming eruptions are the effects on global climate and thus on
global socioeconomics. Historical caldera-formations such as at Tambora in 1815,
at Krakatau in 1883 and at Pinatubo in 1991, although several orders of magnitude
smaller than the largest prehistoric eruptions, appear to have had a significant
impact on our climate, including visible atmospheric effects such as bizarrely
coloured skies, halos around the sun and the moon, vibrant sunsets and sunrises and
anomalously cold weather conditions leading to crop failure and famine.
Since volcanoes and their eruptions are merely the surface manifestation of
large-scale magmatic processes operating in the Earth’s interior, calderas also
provide key insights into the generation and evolution of large-volume silicic
magma bodies (Self et al., 1984, 1986; Lipman, 1984, 2000). Volcanic processes are
the culmination of a complex interaction of geological processes occurring at
global, regional and local scales and the study of volcanoes (including collapse
calderas) provides us with relevant information on lithospheric dynamics.
The relationship between caldera formation and pyroclastic activity became
evident after the historical eruption of Krakatau in 1883 (Verbeek, 1886). Verbeek
noted that the volume of the deposits was much less than that of the missing
structure. Consequently, he rejected the idea that the mountain had been blasted
away and concluded that most of the mass had foundered into the space evacuated
by a rapid discharge of huge volumes of magma. Earlier, Fouque ´ (1879) inferred
from similar reasoning, that the bay enclosed by the islands of Thera and Therasia in
Santorini had resulted from a collapse associated with a strong pyroclastic eruption.
Fouque ´ concluded that whatever the mechanism, it was the collapse of the roof
that had triggered the explosive eruptions. The main explosive discharge was the

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