Environmental Engineering Reference
In-Depth Information
Figure 2.2 Exposed section through the Youngest Toba Tuff ash fallout at
Jwalapuram in India. Only the 5 cm or so at the base (at the level of the foot of
the ladder) is fallout from the ash cloud. The pale-grey deposits reaching up to
ankle-level of the man on the ladder are composed of near-pure ash sourced by
reworking of tephra fallout that must have covered the surrounding slopes of the
Jurreru valley. Prominent horizontal bands in this reworked ash are
'
representing periods of aridity and desiccation. This sequence appears to represent
'
hardpans
five or six monsoon cycles. Above these layers, there is a darker ash-rich deposit,
which may be associated with a period of aridity. And above this is an even darker
layer of sediments composed of sands and silts. Optically-stimulated lumines-
cence dates suggest that the section spans less than a few thousand years either
side of the Youngest Toba Tuff eruption (Petraglia
et al
.,
2007
). Strata above and
below the ash-rich layers contain abundant Middle Palaeolithic tools.
very challenging to make progress on unravelling the Toba story on account of the
eruption
'
s timing during a period of very signi
cant climate oscillations
(Dansgaard
Oeschger cycles), and uncertainty in the co-emitted quantity of sulfur
reaching the stratosphere, which is critical for evaluating climate forcing
(e.g. Oppenheimer
et al
.,
2011
). While it remains problematic to match the
-
ndings
of modelling studies with relevant palaeoclimate data, it is possible to compare
the various climate models for extremely large sulfur releases to the atmosphere
