Environmental Engineering Reference
In-Depth Information
2
On the nature and consequences of super-eruptions
clive oppenheimer and amy donovan
2.1 Introduction: what are super-eruptions and super-volcanoes?
Super-eruptions have been described as
'
the ultimate geologic hazard
'
(Self and
Blake,
2008
). Volcanological use of the term
can be traced at least
back to the title of a 1992 paper on the 74 ka Youngest Toba Tuff eruption in
northern Sumatra (Rampino and Self,
1992
). However, it is the British Broadcast-
ing Corporation (BBC) that can be credited for the proliferation of the terminology
(following a 2000 broadcast), both in the scienti
'
super-eruption
'
c sphere and beyond. While not
'
'
all volcanologists like the term
super-eruption
(perhaps considering it is being
'
'
used more for
Wilson and Charlier,
2009
), it is broadly
understood (e.g. Sparks
et al
.,
2005
)todene a pyroclastic eruption of magnitude,
M
, of 8 or above, where (Pyle,
2000
):
convenience or effect,
M ΒΌ
log
10
(mass of erupted material in kg)
-
7
This threshold thus represents a mass of 10
15
kg. Taking a pumice density of
1000 kg m
-
3
, the bulk volume of a super-eruption deposit would exceed 1000 km
3
,
corresponding to a dense magma volume of approximately 450 km
3
. While silicic
lava (effusive) eruptions can be very large, none approaching this volume has
yet been identi
ed. The term
'
super-volcano
'
may be just as contentious as
'
super-
eruption
'
but it is also prevalent in the scienti
c literature, and we consider the
de
nition proposed by Miller and Wark (
2008
) appropriate: a
'
super-volcano
'
is a
volcano associated with one or more super-eruptions.
Notwithstanding the damping effects of the logarithmic term in
Equation (2.1)
,
when it comes to reporting eruption magnitudes, it is important to note the consider-
able uncertainty attached to estimates of eruption volumes or masses. Estimates for
super-eruption deposits are typically based on mapping or estimating the thickness
