Environmental Engineering Reference
In-Depth Information
14
Volcanic emissions: short-term perturbations, long-term
consequences and global environmental change
tamsin a. mather and david m. pyle
14.1 Introduction
Volcanism plays a vital role in the outgassing and cycling of major gases and other
volatiles between the Earth
'
s mantle and its surface reservoirs. As explored elsewhere
in this topic, volatile-cycling by volcanism is one of the key mechanisms by which
processes
within
our planet drive change at the surface. Earth
'
s surface response to
volcanism has been suggested to be catastrophic in nature over both shorter (10
1
10
2
-
years, e.g. following Toba-scale explosive eruptions) and longer timescales (10
5
10
6
years e.g. large igneous provinces). However, volatile outgassing and recycling have
also played a major role in the development and maintenance of Earth
'
s atmosphere,
contributing to the persistence of conditions on the planet required for life to emerge
and evolve (e.g. Schaefer and Fegley,
2007
). For example, on geological timescales it
is hypothesised that atmospheric carbon dioxide (CO
2
) concentration is regulated by
a dynamic equilibrium between volcanic outgassing and consumption by chemical
weathering of silicate minerals and deposition of carbonates (since
-
200 Ma, e.g.
Berner
et al
.,
1983
). This stabilising mechanism has been invoked as one of the key
attributes that allowed Earth to become and remain habitable (Kasting and Catling,
2003
). However, proxy records suggest that CO
2
concentrations have varied signifi-
~
-
cantly over the last 500 million years (e.g. Wallmann,
2001
). Many explanations are
proposed for this variability but signi
cant
fluctuations in the
'
background
'
carbon
flux from the world
'
is volcanoes is one likely piece of the puzzle.
Magmatic gases are generally dominated by water and CO
2
. However, in much
of this chapter we focus on sulfur dioxide (SO
2
): (a) due to its importance in
Earth
'
s radiative balance following conversion to sulfate aerosol
(see also
Chapter 13
) and (b) because it is generally the best quanti
ed volcanic gas species
due to its low concentration in the background atmosphere, and the availability
