The geological record contains evidence of rare, explosive
supereruptions that have covered whole continents with
volcanic ash and have global long-term recurrence intervals
estimated to be in the range of 100,000–200,000 years.
Supereruptions have been defined as eruptions yielding in
excess of 1
kg of magma (>450 km
; Sparks et al. 2005).
Extremely rare examples have produced vast amounts of
kg, or 4500 km
). Supereruptions lead to
caldera collapse, the formation of huge sheets of pyroclastic
flow deposits (ignimbrites), as well as very extensive ash-fall
layers and injection of noxious gases into the atmosphere.
The effects of a future supereruption will therefore be more
violent and damaging than those of the considerably smaller
eruptions that society has experienced in historic times.
The immediate effects of a supereruption will be almost
unimaginably severe. Yet sooner or later, another one will
occur, and future societies must be aware of, and prepared
for, the consequences. Unlike other extreme natural hazards,
there may be some degree of warning of an impending
supereruption (Lowenstern and Hurwitz 2008 this issue).
Furthermore, supereruptions are potentially long-lasting
(continuing at least for many days, and in some cases inter-
mittently for weeks to perhaps years; Wilson 2008 this
issue), compared to a brief but intense major earthquake or
tsunami. The volcanic ash and gases released high into the
atmosphere could have severe worldwide effects on climate
and weather. Thus, huge explosive eruptions are one of the
few natural phenomena that can
produce truly global catastrophic
effects. They also differ from other
hazards (except meteorite impacts)
in producing persistent atmospheric
effects for several years after the
eruption (Rampino 2002).
This article presents an assessment
of the effects of very large explosive
eruptions, which could have con-
sequences well beyond those asso-
ciated with historic volcanic activity.
We begin with brief descriptions of
the eruption style and the deposits
that are produced, the gases that are
released, and how we study them.
We then turn to the duration,
recurrence, and effects of supererup-
tions, including their atmospheric
impact, and consider their poten-
tial influence on global tempera-
ture and weather. Finally, we discuss issues facing society
after a supereruption, including potential socio-economic
impacts. Predicting all of the effects of supereruptions is
problematic because many are outside modern experience.
PRODUCTS AND STYLES OF SUPERERUPTIONS
We have chosen here to assess the effects of a supereruption
in the range of 2000–3000 km
of magma [4–7
Magnitude 8.6–8.8 (Pyle 2000; see Miller and Wark 2008 this
issue), equivalent to 5000–8000 km
of volcanic ash
deposits], an eruption like the largest from the Toba
(Indonesia) or Yellowstone (USA) supervolcanoes. All
supereruptions are associated with the formation of a