Page 179 - Fundamentals of Physical Volcanology

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156 CHAPTER 10

quent eruptions of small magnitude and intensity of
these three centers is repeated at many other active
centers around the world such as Hekla in Iceland
and Piton de la Fournaise on Réunion Island in the
Indian Ocean.
The largest eruptions listed in Table 10.4 are, by
contrast, rare and highly destructive events. The
1815 eruption of Tambora on Sumbawa Island in
Indonesia, for example, was responsible for the
deaths of ∼92,000 people, 90% of them from starva-
tion and disease in the aftermath of the eruption.
The eruption in April 1815 produced an eruption
Fig. 10.6 A thin lava flow surrounding a house in the town
column which reached a height of between 40 and
on Kalapana on the sotheast flank of Kilauea volcano,
50 km. The spreading eruption cloud was so dense
Hawai’I. (Photograph by Jim Griggs, courtesy U.S.
Geological Survey, Hawaiian Volcano Observatory.) that it plunged a region up to 600 km downwind
of the volcano into darkness for periods of up to
2 days. The dispersal of particles from the cloud
the former category are eruptions such as the ones through the stratosphere is thought to have been
listed for Kilauea and Mauna Loa volcanoes in responsible for short-term climate change, the year
Hawai’I. The listed Kilauean eruption is just one of following the eruption, 1816, being known as the
30 which have occurred there since 1950 alone. “year without a summer” (see section 12.1).
These eruptions are primarily lava-producing and
are of relatively small volume. This is reflected in
10.6.2 The magnitude of volcanic eruptions
the low VEI value for the eruptions and their low
in the geological record
magnitude and intensity values. Although these
eruptions are relatively small and frequent they can Our perception of volcanic eruptions is that those
still be locally destructive. For instance, the ongo- such as the 1980 Mount St Helens eruption and the
ing eruption which started in January 1983 had by AD 79 eruption of Vesuvius are large, and indeed
January 2001 destroyed ∼180 buildings and 13 km they are when only the time scale of human history
of highway. This includes the almost complete is considered. Eruptions such as the 1815 Tambora

destruction of the village of Kalapana between eruption and the AD 180 Taupo eruption are even
1986 and 1990 (Fig. 10.6). Similarly Table 10.4 lists larger and represent the upper limit of the magni-
one of many frequent eruptions of Etna in Sicily. tude and scale of recent eruptions. However, vol-
Eruptions there are also primarily lava-producing. canologists have studied deposits from eruptions
Eruption styles vary between Strombolian, Hawaiian, which date much further back in the geological
and Vulcanian and relatively violent explosions past, and find that the largest eruptions in the geo-
there do, on occasion, kill people standing too close logical records dwarf the eruptions which humans
to the eruptive vents. For instance, in September have witnessed first hand.
1979, nine tourists were killed and many more Table 10.5 lists a number of the largest volcanic
injured by an explosion at Bocca Nuova, one of eruptions identified in the geological record. It should
Etna’s summit craters. On many occasions lava be noted that the enormous scale of the deposits
flows produced during eruptions on Etna have from these kinds of eruptions means that they are
threatened to destroy or have destroyed villages much less well studied than those from smaller, his-
located on the flanks of the volcano and a number torical eruptions. Even so, comparison with the
of methods have been tried to divert or stop the historical eruptions in Table 10.4 shows the large
flow of lava there (see section 11.5). In 1992, for scale of these eruptions compared with eruptions
example, a lava flow came within 700 m of destroying observed in the recent past. For example, the
the village of Zafferana Etnea. The pattern of fre- May 1980 eruption of Mount St Helens seems a