Environmental Engineering Reference
In-Depth Information
estimate that the 60,000 km
3
rhyolites from the Afro-Arabian province may have
released as much as 9
10
5
Tg SO
2
. In contrast, the metaluminous silicic
-
15
-
magmas from the Paraná
Etendeka province, likely the products of crustal
melting, may not have been volatile saturated at depth, and had much less capacity
to carry dissolved sulfur (estimated total release of up to 1
10
4
Tg SO
2
from
the 20,000 km
3
rhyolites from the Paraná province).
There are limited estimates of carbon dioxide emissions for continental
ood
1,000 km
3
pulses of Deccan activity lasting 10
-
50 years at 1.4
-
11 Pg CO
2
in
total, or
1,100 Tg/yr. In contrast to SO
2
, this CO
2
injection is trivial
compared to the atmospheric reservoir (currently
~
220
-
10
6
Tg CO
2
and likely
higher at the end of the Cretaceous), and hundreds to thousands of years between
eruptive episodes would allow the atmosphere suf
~
3
cient time to re-equilibrate
(Self
et al
.,
2006
).
(iii) Feedbacks from the Earth
'
s surface modulating the rate/style of volcanism
While
flood basalt volcanism may be the most spectacular symbol of the potential
link between volcanism and global change, more subtle long-term changes in the
rates of global volcanism have also been proposed to perturb the global environ-
ment over Earth history. The major feedbacks that have been explored are those
between the hydrological cycle and volcanism. Although short (annual) timescale
feedbacks have been proposed (Mason
et al
.,
2004b
), feedbacks on longer time-
scales such as glacial cycles have received more attention and have more relevance
in terms of the links between volcanism and global change.
Many studies have discussed the possible coupling between volcanism and
glaciation. In the 1970s, Bray (
1977
) postulated that volcanism might have driven
Pleistocene glaciations. The reverse hypothesis, that rapid climate change leading
to ice-retreat, glacial unloading, and sea-level change might trigger volcanic
activity, was proposed by Rampino
et al
.(
1979
). Subsequent work has revealed
a number of more- or less-compelling examples where this hypothesis might hold.
There is strong evidence for a burst of subaerial volcanic eruptions in Iceland
shortly after the last glacial maximum (LGM) with time-averaged eruption rates
several times higher than at present (Sigvaldason
et al
.,
1992
; Maclennan
et al
.,
2002
). There is also weak evidence for increased continental eruption rates in
both northern Europe and eastern California following deglaciation, over several
glacial cycles (Glazner
et al
.,
1999
; Nowell
et al
.,
2006
). Each of these settings,
however, features volcanism that results from decompression melting of the
mantle, and where decompression following ice removal may lead to increased mantle
melt production (e.g. Jull and McKenzie,
1996
; Pagli and Sigmundsson,
2008
).
