Environmental Engineering Reference
In-Depth Information
17
The environmental and climatic impacts
of volcanic ash deposition
morgan t. jones
17.1 Introduction
Explosive volcanic eruptions rapidly inject a mix of gases, aerosols and solids into
the atmosphere, leading to the wide dispersal of ejecta. The solid particles erupted
by a volcano consist of igneous minerals, fragments of country rock, and volcanic
glass in varying abundances. The mineral species and volcanic glass compositions
are determined by the chemistry of the parent magma. A considerable fraction of the
airborne solids (tephra) is volcanic ash, de
ned as
<
2mminsize(RoseandDurant,
fine-grained nature of volcanic ash allows for
transportation thousands of kilometres from the source prior to deposition. The
largest known eruptions can eject
>
10
16
kg of material in a single event (Mason
et al
.,
2004
), capable of blanketing whole continents and/or extensive swathes of the
ocean floor with deposits several centimetres thick (Self,
2006
;
Figure 17.1
).
Ejected volcanic volatiles cool as they mix with the atmosphere, forming salts,
condensed gases, and aerosols (
Figure 17.2
). Co-erupted solids act as nucleation
surfaces for such phases (Delmelle
et al
.,
2007
; Oskarsson,
1980
). These soluble
surface coatings, termed ash-leachates, are comprised of sulfur species and
halogens as the main anion donors and signi
cant concentrations of many alkali
and transition metals as cation donors (Frogner
et al
.,
2001
). Up to 40% of the
erupted SO
2
and 10
-
20% of HCl can be scavenged from volatile phases onto
particle surfaces in this manner (Rose,
1977
). Ash-leachate chemistry and volume
varies substantially between different eruptions as a function of geological setting,
eruption size, plume concentration, and magmatic chemistry (Jones and Gislason,
2008
; Witham
et al
.,
2005
).
Volcanic ash deposition can have substantial impacts on both terrestrial and
oceanic ecosystems, the extents of which can be global and long-lived. Many of
