Environmental Engineering Reference
In-Depth Information
use the amounts of gas released by different types of volcanic activity as an
indication of the scale of these effects.
'
Present-day
'
emissions of SO
2
, measured at the world
'
s volcanoes since the
advent of ground- and satellite-based ultraviolet (UV) spectrometers in the late
'
passive
'
emissions to the atmosphere, such as those from the ongoing 30-year-
long eruption of K
ī
lauea (Hawai`i), where most degassing is from lava lakes
or lava
flows; and from sporadic explosive or non-explosive eruptions of varying
sizes (e.g. Pinatubo and Hudson in 1991 and Nyiragongo in 2002). Previous
compile the contributions from these different types of volcanism over the modern
period of observations and time-average in some way. For example, Pyle and
Mather (
2003
) estimated that
~
40% of the time-averaged
flux was from continu-
ous
40% from sporadic emissions from smaller explosive
eruptions (
<
10
13
kg tephra, 20
'
passive
'
degassing,
~
-
30 eruptions/yr),
~
10% from sporadic emissions
from non-explosive eruptions (1
10% from sporadic
emissions to the stratosphere from larger explosive eruptions (
>
10
13
kg tephra,
1
-
2 eruptions/yr) and
~
2 eruptions/century).
The environmental consequences of these time-averaged emissions may
range from local impacts on farmland and animal and human health from down-
wind fumigation by persistent, non-explosive degassing volcanoes (e.g. Masaya in
Nicaragua; Delmelle
et al
.,
2002
), to the global effects recorded in terms of
temperature decrease and ozone depletion after sporadic but relatively large
eruptions into the stratosphere (e.g. the 1991 eruption of Pinatubo).
Table 14.2
summarises SO
2
emissions estimated from the Pinatubo (1991, largest eruption of
the satellite era), Tambora (1815, largest historic eruption) and the Young Toba
Tuff (
-
74 ka, largest Quaternary eruption) eruptions (see also
Chapter 2
). There is
convincing historical evidence for the impacts of Tambora (Oppenheimer,
2003
)
and, although their degree is debated, Toba
'
is environmental impacts were certainly
widespread; unsurprising, given the short timescales of release and their wide
dispersal (e.g. Petraglia
et al
.,
2012
; Timmreck
et al
.,
2012
).
While the short-term injection of SO
2
was signi
~
cant in each of these cases, we
can illustrate the contributions of eruptions of these sizes to
'
background
'
planetary
outgassing by considering the size
-
recurrence interval relationships. The Pinatubo
eruption injected 12
26 Tg of SO
2
into the atmosphere, with 20 Tg often taken
as the accepted value (McCormick
et al
.,
1995
; Krueger
et al
.,
1995
). Based on
the geological record, a Pinatubo-sized eruption occurs on average about every
100 years (Pyle,
1995
). Thus, the time-averaged SO
2
-
flux from Pinatubo-scale
eruptions is about 0.2 Tg/yr. This is almost two orders of magnitude smaller than
the measured present-day global volcanic SO
2
flux and shows that while Pinatubo
