Volatile release from flood basalt eruptions: understanding the potential environmental effects - Volcanism and Global Environmental Change - page 169

with a duration of 3 4 days. Assuming the CRBG is typical of CFB emplacement

characteristics, it thus seems likely that individual CFB eruptions could have
in

-

uenced climate on timescales of decades to centuries if the eruptions were
sustained.

11.3 Emplacement characteristics and volatile release rates of
flood basalt eruptions
The most abundant volatile species released during a basaltic eruption is H 2 O (50%
to 90% by volume of the gas phase) followed by CO 2 and SO 2 , either of which
may contribute up to 40% by volume. Halogens are released in minor quantities
mainly in the form of HCl, HF, and with even lower abundance of HBr and HI.
When attempting to constrain volatile fluxes from CFB provinces, eruption

characteristics of individual CFB eruptions are important considerations. During
the emplacement of CFB provinces, hundreds to possibly thousands of eruptions
produce immense lava 5,000 km 3 . ow- elds with volumes on the order of 1,000 -

All ows (see

Figure 11.1b ), and when examined in detail all CFB provinces are dominated
by compound p

flood basalt lava ow- elds are dominated by basaltic lava

elds (Bryan et al ., 2010 ). In terms of eruption
style, these lava-forming eruptions produce

ā hoehoe lava ow-

fire-fountains at the vents, just like
recent Hawai`ian or Etnean eruptions as discussed above.
Constraining the timing and length of hiatus periods within a province-forming
sequence of eruptions is as important as knowing the durations of eruptions in
order to assess the environmental effects of CFB volcanism (Self et al ., 2014 ) . For
the Grande Ronde Formation of the CRBG ( Figure 11.1a ), there were

~ 100 separ-

ate eruptions within a maximum of 400,000 years (Reidel and Tolan, 2013 ).

Assuming that each eruption lasted 100 years, then the average hiatus would have
been

~

4,000 years. In reality, both the number of eruptions and the total duration
of their emplacement are highly uncertain and in any case this average hiatus may
not be typical of the durations between any two individual eruptions.
Basaltic magmas (including those forming

~

flood basalts) are usually rich in
dissolved sulfur (commonly with sulfur concentrations of 1,500 ppm, Wallace,

2005 ; Black et al ., 2012 ). Therefore, the release of sulfur-rich gases from a large
basaltic eruption can be much greater than that from an explosive silicic eruption
of equal size. It is also known that the erupted basaltic magma is not the only
source of volatiles during the emplacement of CFB provinces. In particular, for
the Siberian Traps, several authors note the potentially important role of gases
released via interactions between the magma and country rock (e.g. Ganino and
Arndt, 2009 ; Svensen et al ., 2009 , Chapters 10 and 12 ).