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To what extent can preparedness and planning
mitigate the effects of volcanic hazards?
Dan Brown
There are several ways that we can mitigate the effect volcanic
hazards by being prepared and by have
good systems in place, from evacuation plans combined with
sophisticated monitoring, found on
Montserrat, as well as building defences in order to try and
divert flows of debris, tephra and lava. In this
essay I will explain how various methods have proved to be
either successful or maybe not so.
On Montserrat, the MVO was set up in 1996, prior to the eruption
of Chances Peak that same year. It
aims to monitor, by using a combination of GPS receivers,
seismometers, pH as well as temperature
sensors, the tectonic activity deep beneath the volcano to
predict when it will erupt within the widest
window possible; it is thought that an event can be foreseen 2-3
hours before it occurs, enough time to
save most lives. This latter statistic is shown as only 16
people lost their lives in one of the most violent
and prolonged eruption on record. On the other hand whilst the
MVO can aid with evacuation, there are
no defences on Montserrat to prevent volcanic hazards (such as
pyroclastic flows) from destroying
property. Two thirds of the island was buried as a result of the
last eruption and the capital in particular
was covered in up to 12m of fine grained ash.
The Washington authorities also set up an evacuation plan long
before Mt St Helens erupted in 1980 as it
is historically known for its explosive nature. It featured two
zones; a red zone with a 10km radius
surrounding the crater which forbid all activity, and a blue
zone which permitted some limited forestry
work. Like on Montserrat, instruments such as seismometers were
put in place to try and predict when
the volcano would erupt so that the plan could be put into
action. Unlike the MVO however the systemswere more rudimentary and
as a result, the true scale of the eruption wasnt recognised,
leading to the
creation of a false sense of security within the local
population. Because of this despite the warnings (that
werent strong enough) people such as Harry Truman strayed into
the red zone, costing them their lives.
In hindsight the red zone wasnt large enoughas pyroclastic flows
reached 17km from the crater in
places, and it was only down to luck that more lives werent lost
due to the fact that the eruption
occurred on a Sunday and so, no work was taking place in the
blue zone at the time. As well as poor
planning, the inhabitants surrounding the volcano werent very
prepared for the eruption either. There
was a shortage of dust masks which was a big problem as the
volcano emitted a large amount of fine
grained ash that, if inhaled could severely damage peopleslungs
due to its silica content.
Similarly, Mt Vesuvius near the city of Naples in Italy also
features a tiered evacuation plan and it too, like
Mt St Helens was in 1980, long overdue an eruption. A red zone
(12km radius of the crater) denotes the
populated area that would be directly affected by deadly
pyroclastic flows. The blue zone extending a
further 10km north west of the crater is at risk of mud flows,
and an extensive yellow zone to the east of
the volcano is thought to be engulfed in ash, and such may need
to be evacuated to protect inhabitants
from roof collapse; an impact all too familiar when a similar
fate buried the population of the ancient
town Pompeii in 79 AD. Also like Mt St Helens and Chances Peak,
Mt Vesuvius is extensively monitored
(its the most heavily monitored volcano in the world today).
Scientists fear however, that despite best
efforts to be prepared, the Italian authorities havent thought
the plan through. Currently it assumes that
600,000 people will required to be evacuated in a period of 72
hours however the city of Naples
approximately 10km west of the volcano isnt included in this
plan and so residents are left with a false
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sense of security. Furthermore, the logistics of evacuating an
extremely large volume of people,
especially using the complex network of narrow roads that make
up the bay of Naples, arent very
realistic.
Like in the eruption of chances peak on Montserrat, when Mt
Pinatubo on the Filipino island, Luzon in
June 1991 it too emitted large amounts of material; clouds of
ash blocked out the sun turning day tonight, and when it settled it
left a 15cm covering on many of the local roads. Furthermore,
lahars and
pyroclastic flows were also present. Prior to the eruption,
houses were built with steep pitched roofs so
that ash wouldnt collect on them, lessening the risk of roofs
collapsing. Despite this precaution 42,000
homes were destroyed as a result of falling pumice and it was
only down to a successful evacuation plan
that the death toll from building collapse was limited to only a
few hundred. The roofs also didnt protect
houses from lateral moving lahars and pyroclastic flows which
also destroyed thousands of buildings.
Because of this, since the last eruption, new buildings have
been built on stilts so as to allow mudflows to
pass harmlessly underneath. Another example of good preparation
in the lead up to the eruption was the
creation of many evacuation camps by the Red Cross. This was
effective as it gave shelter to a high
number of refugees whom had lost their homes (200,000 people
were still displaced 4 months after theeruption and 50,000 families
permanently lost their homes). These camps, whilst initially
successful soon
became as deadly as the eruption itself as diseases such as
measles spread. Five hundred people died
from disease compared to the 847 deaths directly connected to
the volcano. Despite this though the
evacuation of the area surrounding Mt Pinatubo on whole was one
of the most successful in history, as
around 200,000 people were relocated and so the fact only 1347
people died in total is remarkable. The
success is down to a combination of an accurate prediction (due
to precise monitoring of earthquakes
and SO2 emissions) and an MEDC presence; the US Air Force was
stationed on Luzon and so vital
equipment and aircraft were at immediate disposal.
So far the main hazards that Ive mentioned havebeen ash clouds,
lahars and pyroclastic flows. When Mt
Etna in Sicily erupted in 2002 however lava flows were the
prominent hazard due to the fact that it emits
low viscosity, basaltic lava. In the winter of 2002, a front of
lava consisting of 3 individual flows, moved
down the southern flank of the peak towards the skiing village,
Rifugio Sapienza. The flow was 400 yards
wide and up to 25ft tall in places however it moved at a slow
pace (approx. 24 yards/hour), giving local
residents time to prepare before it engulfed the village.
Several defences were erected; firstly many of
the buildings were covered in earth, in hope that the lava would
flow over them, and secondly lava
barriers were set up in order to divert the flow away from the
village. In the end the barriers were
overtaken and whilst no lives were lost many of the ski resorts
were destroyed (impacting the tourism
industry that over 500 people depend on) as well as extensive
areas of farmland lower down the slopes
of the volcano.
In conclusion, on one hand planning well and being prepared, by
monitoring volcanos in order to predict
when eruptions will occur, and evacuating areas suspected of
being directly affected by volcanic hazards
such as lahars and pyroclastic flows, the loss of human life can
be drastically reduced. The best example
of this is the eruption of Chances Peak on Montserrat, as the
state of the art MVO helped to precisely
pinpoint areas that would soon be engulfed by lahars, areas
which were subsequently evacuated.
Because of this only 16 people died on an island that is very
densely populated. The same was true when
Mt Pinatubo erupted in 1991. On the other hand however, it is
very difficult to prepare by building
defences such as barriers and houses that can withstand volcanic
hazards; the force of the earth is too
great for us to control. This was seen in Sicily when lava flows
from Mt Etna overflowed the barriers put
in place and destroyed many of the nearby ski resorts.
