Environmental Engineering Reference
In-Depth Information
re
uenced magma fragmentation processes at the vent.
The phase changes associated with the interaction of water with magma may
impact on the dynamics of explosive eruptions, resulting in alternating phases of
Plinian eruption and fountain collapse, and injection of ash into the atmosphere
at multiple heights (Van Eaton
et al
.,
2012
). Further research in this domain
seems warranted since many super-volcanoes are presently occupied, at least
partially, by bodies of water.
ecting the water-in
2.4 Where are the super-volcanoes and when did they erupt?
Mason
et al
.(
2004
) catalogued 42
M
8 or larger eruptions spanning the last 36 Ma.
However, these events were strongly clustered in both time and space, with clusters
between 36 and 27 Ma ago, and from 13.5 Ma ago up to the present. While
tectonics may play a role in the triggering of super-eruptions (e.g. Allan
et al
.,
2012
), super-volcanoes are found in association with mantle plumes, rifts and
subduction zones. However, there are strong biases in the dataset that are readily
evident from consideration of the geographic distribution of events
all but four of
them are located in the Americas (32 in North America, six in the central Andes).
The others are in Sumatra (Toba), New Zealand (Taupo) and the Ethiopian plateau.
The more recently compiled
-
'
(LaMEVE) database lists over 20
M
8 and above eruptions spanning the past 2.2
Ma, suggesting a return period of around 100 ka (Crosweller
et al
.,
2012
).
A notable difference between the Mason
et al.
(
2004
) and LaMEVE databases is
that the latter identi
'
large magnitude explosive volcanic eruptions
es six Quaternary super-volcanoes in Japan. However, it is
likely that many other super-eruption deposits remain undiscovered or unrecog-
nized (Donovan and Oppenheimer,
2014
).
Recently, a case has been made for super-eruptions having occurred on
Mars (Michalski and Bleacher,
2013
), although the geomorphological evidence
presented may not prove compelling for some volcanologists.
2.5 Products of super-eruptions
As we have seen, the deposits of super-eruptions can be far
flung, yet also concen-
trated locally at the site of the associated caldera. This section provides an
overview of these diverse materials.
2.5.1 Tephra fall
One of the astonishing aspects of super-eruption deposits is the areal extent of
tephra fall, sourced largely
-
perhaps exclusively
-
from the co-ignimbrite plumes
