Environmental Engineering Reference
In-Depth Information
16
Halogen release from Plinian eruptions and depletion
of stratospheric ozone
kirstin kr ยจ ger, steffen kutterolf and thor h. hansteen
16.1 Introduction
Plinian eruptions are characterized by large mass eruption rates and high eruption
columns. They inject gases (water vapour, carbon dioxide, sulfur dioxide and
halogen compounds) and solid particles (e.g. ash) directly into the stratosphere
(Walker,
1973
; Textor
et al
.,
2003a
; von Glasow, 2009), where they in
uence the
atmospheric composition and chemistry, in particular sulfuric acid aerosol and
ozone concentrations as well as the radiation budget (Robock,
2000
; Timmreck,
2012
; see also
Chapter 13
). If a Plinian eruption takes place in the tropics, the
climate in
uence is global, due to the spread of volcanic relevant gases by the
Dobson circulation in the stratosphere (Toohey
et al
.,
2011
). Based on
stratospheric circulation timescales sulfur and subsequently formed particles have
a residence time of 3
-
6 years. Therefore they have the ability to cool the surface
climate and affect the ozone layer for a few years. If large amounts of volcanic
halogens reach the stratosphere, they have the potential to further enhance the
depletion of the ozone layer (Stolarski and Butler,
1978
; Mankin and Coffey,
1984
). Ozone in the stratosphere protects the Earth
'
s surface from the harmful
ultraviolet (UV) radiation. Recent model studies revealed substantial ozone deple-
tion and UV ampli
-
Brewer
cation due to the Siberian Traps volcanism during the end-
Permian (Beerling
et al
.,
2007
; Black
et al
.,
2014
; see also
Chapter 20
).
Most large explosive eruptions occur in subduction-zone settings (also called
volcanic arcs), where the magmas are typically water-rich and reach
fluid over-
saturation at depth, which in turn represents a major driving force for the explo-
sivity. The high volatile contents in subduction-zone magmas originate from
dehydration and partial melting of the subducted oceanic plate. Subduction-zone
volcanism occurs at nearly all latitudes, and probably represents the volumetrically
