Geography Reference
In-Depth Information
Plates 5.1 and 5.2
The
lower part of the 1992-3
basaltic lava flows on the
eastern flanks of Mount
Etna. In plate 5.1 (top) the
town of Zafferana Etnae can
be seen in the distance,
approximately 500 m from
the distal end of the flow. In
the foreground is a
collapsed lava tube. Plate
5.2 (bottom) shows where
the lava stopped in the
garden of a house on the
outskirts of the town. Local
culture attributes the
cessation of the flow to
divine intervention by the
Madonna of Providence,
whose statue was brought
in procession to this point,
but science attributes it to
the lava modification
experiments and the end of
the eruption that caused the
flow.
of volcanic vents (at least one per km
2
), the length
of lava flows (up to 15 km), the location of urban
settlements (of which there are thirty-seven), and
the pattern of valleys down which lava might flow
(44 per cent of land below 2000 m is susceptible;
Duncan
et al
. 1981). The response to this hazard
has included one of the most ambitious and
technically demanding lava flow diversion
experiments ever mounted. From 14 December
1991 to 30 March 1993, in 473 days of continuous
eruption, Etna disgorged 250 million m
3
of lava
over an area of 7 km
2
. In order to protect the 7000
inhabitants of Zafferana Etnea, artificial channels
were dug and lava flows were dammed with
370,000 m
3
of earth. Complicated blocking tactics
were used and lava levees were thinned with 7000
kg of explosives in order to retard the flow
(Barberi
et al
. 1992).
There are several reasons why volcanic hazards
zonation is eminently practicable. One is that
many volcanoes offer a clear series of precursory
signs of impending eruption, while another is that
the characteristic styles, locations and frequencies
of eruptions can be deduced from stratigraphic
evidence. This means that zonal maps can be
constructed on the basis of knowledge of the
