Environmental Engineering Reference
In-Depth Information
most important subaerial explosive volcanism in the tropics (Schmincke,
2004
).
This kind of explosive eruption also comprises higher amounts of the volatiles
sulfur and halogens compared to hot-spot and rift-related volcanism, which is
especially true for chlorine (Scaillet
et al
.,
2003
; Pyle and Mather,
2009
; Mather
et al
.,
2012
; Shinohara,
2013
). Large subduction-zone eruptions in the tropics
therefore have a high potential to in
uence climate and atmospheric composition,
including ozone depletion (Metzner
et al
.,
2012
; Kutterolf
et al
.,
2013a
).
Following an introduction on halogen outputs from Plinian eruptions, this
chapter gives an overview about novel measurements to detect bromine (Br) and
chlorine (Cl) masses emitted from large explosive subduction-zone eruptions in the
past. Literature data of volcanic emissions are combined with detailed
field data
and chemical measurements of the halogen release from the entire Central American
Volcanic Arc (CAVA) covering the last 200 kyr. Our mass budgets are based on
petrological data obtained by microchemical analyses of Br and Cl in representative
melt inclusions in minerals and the corresponding matrix glasses (Kutterolf
et al
.,
2013a
; unpublished), and scaled according to mass estimates of the eruption products
(Kutterolf
et al
.,
2008
, and references therein). Finally, this chapter addresses the
potential role of halogen release from large, tropical eruptions on the stratospheric
halogen burden and evaluates their potential impact on the ozone layer. The in
uence
of volcanic emissions on the troposphere is addressed in
Chapters 13
and
14
.
16.2 Halogen output from Plinian eruptions
A number of studies have been performed on the Cl output of large explosive
eruptions (Devine
et al
.,
1984
;Symonds
et al
.,
1988
;Gerlach
et al
.,
1996
). Volatile
masses released from single eruptions have typically been estimated using the
petrologic method (Johnston,
1980
), in which the difference between pre-eruptive
volatile concentrations measured in glass inclusions in minerals and those in the
degassed tephra particles are scaled up using the erupted mass of previously mapped
volcanic products. Another approach used for modern eruptions is to estimate the
erupted sulfur mass in the gas phase with satellite-based instruments (Krueger,
1983
;
Carn
et al
.,
2003
;Theys
et al
.,
2013
), and thereafter derive the Cl contents using an
assumed Cl/S ratio (Giggenbach,
1996
;Halmer
et al
.,
2002
). Mass balance calcula-
tions using prescribed Cl/S ratios are problematic due to the large natural variations
of Cl/S ratios in magmas, which are further enhanced by degassing processes. Thus,
global estimates of Cl output from large eruptions based on a combination of both
petrologic Cl data and indirect estimates are hampered with comparatively large
errors, which may reach one to two orders of magnitude (Aiuppa
et al
.,
2009
).
Recent reviews of the data used for such global compilations are given by Scaillet
et al
.(
2003
), Fischer (
2008
), Pyle and Mather (
2009
) and Shinohara (
2013
).
