Environmental Engineering Reference
In-Depth Information
Figure 14.2 The time-averaged volcanic SO
2
ux to the stratosphere (Mt/yr)
and erupted tephra
flux (Gt/yr) from explosive volcanic eruptions of different size
(magnitude, M; Pyle
et al
.,
1996
). The tephra
flux is calculated from the rates of
explosive volcanism over the past 2,000 years (Pyle,
1995
), while the SO
2
flux is
calculated from the relationship between eruption size (M) and SO
2
release
determined for eruptions with M3
6, adjusted for the amount that reaches the
stratosphere (Pyle
et al
.,
1996
). Uncertainty in the sulfur emission rate is likely to
be of the order of a factor of 2. Gas emissions decline slightly from M4
-
7,
because smaller (M3, 4) eruptions tend to be more S-rich per unit mass of magma
(basalts, andesites) than (M6, 7) eruptions (dacites, rhyolites). Both
-
uxes drop
off for large magnitude eruptions (M8, 9), re
ecting their much lower recurrence
rates (Mason
et al
.,
2004a
).
magma, making petrological methods challenging to apply; and high concen-
trations in the background atmosphere hinder reliable spectroscopic quanti
ca-
tion. Gerlach
et al
.(
1996
) estimated that the 1991 Pinatubo eruption released
42 Tg CO
2
, about an order of magnitude lower than the current best estimates
for the global annual
flux of CO
2
from
'
background
'
volcanism. Time-averaging
over the
~
100-year recurrence rate of a Pinatubo-scale eruption, this
flux is
insigni
0.4 Tg/yr).
Although there is clear evidence for global effects following eruptions of the
scale of Tambora and Toba, recent modelling studies also suggest that global
temperature perturbations following this type of volcanism recover on decadal
timescales, without tipping the Earth systems into any different mode of behaviour
(Jones
et al
.,
2005
; Robock
et al
.,
2009
; Timmreck
et al
.,
2010
). In the next section
we consider the modes of volcanism that may have the potential
cant (
~
to cause
prolonged and signi
cant perturbation to the Earth system.
