Environmental Engineering Reference
In-Depth Information
(Shoji
et al
.,
1993
), limiting the extent of groundwater contamination but
increasing the incorporation into
flora (e.g. Martin
et al
.,
2009
). This exposes
grazing animals to the effects of
fluorosis (
Figure 17.3C
), such as the mortality
of
>
60% of the sheep livestock in Iceland following the 1783 eruption of Laki
(Thordarson and Self,
2003
).
17.2.2 Radiative changes
Terrestrial ash deposition is capable of initiating changes in atmosphere
-
ocean
circulation through altering surface albedo and by removing vegetation. Volcanic
ash is generally extremely re
ective due to its silica-rich composition and
high particle vesicularity (Jones
et al
.,
2007
). As a result, most ash blankets
will signi
cantly increase the surface albedo (
Figure 17.3D
). The insulation and
increased re
ection of incoming radiation can lead to markedly reduced soil
temperatures below an ash layer (Cook
et al
.,
1981
). The burial of vegetation
diminishes moisture supply to the atmosphere through evapotranspiration
(
Figure 17.3E
), reducing the latent heat
flux and therefore internal atmospheric
convection. This both stabilizes the atmospheric boundary layer and leads to less
recycling of precipitation (Trenberth,
1999
). The combined effects of vegetation
burial and surface-albedo increase become more prevalent with increasing
eruption magnitude. In large-scale scenarios, local effects include a marked
decrease in precipitation, an increase in re
ected shortwave radiation, cooling
from reduced heat retention, and changes to cloud coverage through increased
convective heating (
Figure 17.3F
; Jones
et al
.,
2007
). The climate response to
a large ash blanket varies considerably with latitude, with strong seasonal
amplifications to changes in surface conditions. These modifications manifest
themselves as decadal variations in surface pressures, temperatures and precipi-
tation patterns, which interplay with jet stream locations and strength (Jones
et al
.,
2007
).
17.2.3 Residence times
The surface residence time of an ash blanket at the surface is governed by the rate
of remobilization and erosion, which in turn is controlled by the local geomorph-
ology and climate. Residence times will be shorter in areas of high rainfall and/or
high wind speeds. Finer ash particles are more likely to be resuspended by aeolian
or
fine ash is cohesive and capable of forming a crust
through desiccation, inhibiting erosion, increasing surface runoff (
Figure 17.3G
)
and hindering the re-emergence of vegetation in areas of high deposition (Nammah
et al
.,
1986
). This can initially restrict removal of the ash blanket to incising
fluvial action. However, very
