Environmental Engineering Reference
In-Depth Information
flood volcanism
Flood basalt volcanism releases large quantities of gas over prolonged periods of
time, as well as being associated with huge outpourings of lava and ash onto the
surface of the planet. The link between this activity and evidence of global change,
the style of eruption and its potential impacts are explored in detail elsewhere in
this topic (e.g.
Chapter 11
) but here we consider the signi
(ii) Continental LIPs and
cance of the estimated
gas emissions compared to other modes of volcanism.
Studies of continental
flood basalt provinces show that while the emplacement
of the provinces as a whole may span a million years or so, during this period there
will be pulses of heightened activity associated with the emplacement of individual
flow units (see also
Chapter 11
). As illustrated in
Table 14.2
,
estimated SO
2
emissions for entire individual
10
6
flood basalt provinces range from
~
3
to
10
7
Tg SO
2
. Averaged over a timescale of
7
~
1 Myr, which re
ects their broad
duration, this yields time-averaged SO
2
fluxes of 3.5
-
6.5 Tg/yr for the Deccan
Traps, 6.2
-
10.8 Tg/yr for the Paraná
-
Etendeka and 12.6
-
68 Tg/yr for the Siberian
Traps. These
fluxes represent a signi
cant enhancement (20
-
200%) compared
to the
flux. The pulses of
heightened activity thought to characterise the emplacement of these provinces
means that these broad enhancements include phases of highly elevated
'
present-day background
'
continuous volcanic
ux
separated by hiatuses. For example, the Roza
flow of the Columbia River Basalt
Group may have been emplaced in about a decade (Thordarson and Self,
1996
)
yielding an average SO
2
fluxes of
100
-
1,000 Tg/yr of SO
2
probably characterised decadal-scale pulses of Deccan
volcanism (Self
et al
.,
2006
). These
flux of 1,242 Tg/yr during this period. Similarly,
fluxes would overwhelm global persistent
emissions similar to those seen today, increasing global volcanic sulfur emissions
by 10- to 100-fold during these pulses of activity.
Clusters of large-magnitude silicic eruptions may also be associated with
continental LIP provinces (e.g. Paraná
-
Etendeka and Afro-Arabian LIPs, Bryan
et al
.,
2010
). Like the
are-ups
'
, these provinces can be highly productive, with
total volumes of erupted silicic magma up to
'
10
4
km
3
Etendeka),
and a time-averaged rate of silicic magmatism exceeding 0.05 km
3
/yr (Bryan
et al
.,
2010
). The potential emissions from these silicic provinces may well have been
signi
~
5
(Paraná
-
cant. Scaillet and Macdonald (
2006
) used experiments to investigate the
solubility of sulfur in peralkaline and metaluminous silicic magmas representative
of this type of activity, and found that the origin of the silicic magma is critical to
its capacity to deliver large quantities of volatiles to the atmosphere. In particular,
peralkaline rhyolites that are the products of extensive fractional crystallisation of
basic magma in extensional rift settings like Ethiopia can carry signi
cant amounts
of dissolved sulfur, and yield substantial emissions. Scaillet and Macdonald (
2006
)
