Environmental Engineering Reference
In-Depth Information
flow released about 1,200
Mt of SO
2
per year for a decade or longer. The Grande Ronde Basalts (CRBG)
appear to have released
Thordarson and Self (
1996
) estimated that the Roza
10
6
Mt of SO
2
in intermittent bursts of
<
1
10
3
to 30
10
3
Mt, separated by long-lasting non-eruptive intervals represented by thick soil
horizons in the lava sequence (Blake
et al
.,
2010
). For the Siberian Traps,
estimates of the total SO
2
emissions are in the range 10
~
10
6
Mt of SO
2
(Black
et al
.,
2012
) over the duration of emplacement of the whole province.
Basically, every 1 km
3
-
20
of basaltic magma emplaced during a CFB eruption
releases about 3.5
-
Laki lava
flows and ash indicate that the magma originally contained about 1,700
ppm of sulfur, and that the eruption could have released
~
120 Mt of SO
2
over
8 months (with two-thirds released during the
first 2 months of intense activity;
Thordarson and Self,
1993
).
There are fewer estimates of the halogen content of CFB magmas than for
sulfur. However, studies on the Deccan Traps and the Siberian Traps suggest
that emissions of chlorine and
fluorine might be comparable to those of sulfur
(Black
et al
.,
2012
), or possibly higher (Sobolev
et al
.,
2011
; see also
Chapter 10
).
Lower halogen emissions are suggested from the Paraná
-
Etendeka CFB province
(Marks
et al
.,
2014
).
Estimates of CO
2
released from a CFB province are challenging because direct
determinations of CO
2
degassing from
flood basalt magmas upon eruption are
not available. Self
et al
.(
2006
) used 0.5 wt% as a high, but reasonable, value for
pre-eruptive CO
2
concentration in
flood basalt magmas to estimate that approxi-
mately 14 Mt of CO
2
could be released for every 1 km
3
of CFB lava erupted
(assuming a density of 2,750 kg/m
3
). Therefore, the total release from an erupted
lava volume of 10
3
km
3
(the approximate volume of one Deccan eruption) would
be about 14
10
7
Mt CO
2
from the emplacement of the
entire Deccan Traps assuming a total lava volume of 10
6
km
3
. Although this
estimate suggests that a single eruption can release a very large mass of CO
2
,
this mass equates to only 40% of the current anthropogenic CO
2
10
3
Mt of CO
2
, or 1.4
10
3
Mt/yr; Le Quéré
et al
.,
2013
). If we assume a realistic release timescale of 10 years,
then the volcanic CO
2
ux (
~
35
flux from a single eruption equates to only
~
4% of the
current anthropogenic
ux.
11.4 Towards quantifying the environmental effects of CFB volcanism
The proxy record clearly suggests signi
cant environmental changes that are
temporally coincident (within the uncertainty range of radiometric age dating)
with some periods of CFB volcanism.
Figure 11.4
shows proposed cause-and-
effect mechanisms attributed to CFB volcanism including, amongst others,
