Scientific bulletin 321 - June 2009
©IRD / Michel Monzier
of the famous Avenue
of Volcanoes, rise some
of the largest and most
famous mountains of
fire, doted with evocative
names. Built up high at
over 5000 m altitude,
often covered by
glaciers and permanent
snow, these mountains
overhang the highly
urbanized inter-Andean
valley. With their bouts of
wrath they threaten the
communities living below.
Ecuador has more than
50 volcanoes, seven of
which have erupted since
the arrival of the Spanish
in the 16th Century, and
is the scene of a great
variety of eruption styles.
With the aim of assessing
volcanic hazard,
scientists from IG-EPN1
and IRD characterized
the eruptive dynamics
of some currently
active volcanoes, and
identified those which,
now dormant, might
awaken after a long
rest. Investigation was
therefore made of past
and ongoing eruptions,
to determine their
frequency, intensity and
style2. Further, what
could be done if these
giant systems resumed
activity and provoked
emergency situations?
The team established
eruption scenarios,
produced hazard maps
and set up permanent
observation and warning
systems resulting in the
necessary prevention and
intervention measures.
Eruptions of Tungurahua in October 1999 and November
2007
Ecuador is the scene of some of the
Earth’s most majestic volcanoes.
Stretching along 300 km, between
the Pacific and the coastal plain to the
West and the Amazon to the East, two
mountainous ridges spiked with volcanic cones practically joined to one another cut crosswise through the country
from north to south. A total of 55 volcanoes stand high, peaking as high as
6 000 m altitude and often capped with
glaciers. These colossal structures
threaten 3 million inhabitants of the inter-Andean valley, tightly constrained
between the two Andean cordilleras.
Volcanoes under close watch
It is essential to establish eruption scenarios and set in place suitable preventive and intervention measures. The
IRD researchers and their Ecuadorian
partners1 are therefore closely monitoring three volcanoes that have proved
to be active over the past 10 years:
Tungurahua and Pichincha, which
awoke in 1999, and Reventador, which
suddenly burst into activity in 2002.
The team is also specifically watching
a fourth volcano, Cotopaxi, which has
been showing signs of reactivation
since 2001. The weakest of its eruptions can trigger enormous mud flows,
© IG-EPN/IRD:J. Bustillos
ungurahua, Cotopaxi,
Pichincha: in
T
Ecuador, on either side
Ecuadorian volcanoes:
towards better risk management
or lahars, devastating for the urban
areas below. Indeed most of Ecuador’s
glacier-capped volcanoes threaten to
do so. At 5 897 m altitude, Cotopaxi is
the highest active volcano in the world.
The volcanologists are watching over
each of these volcanoes, to identify the
fluids, gases or solid products emitted, the character of which indicates
the stage of the eruption and helps to
gauge the degree of development of
the magmas amassing in the reservoirs lying under the volcanic mountain. Eruptions can run for months, or
even years. Tungurahua, for example,
has now been erupting for ten years.
The character of the products emitted
changes with the progress of the eruption. Analysis of these can therefore
help unravel the volcano’s process mechanisms and lead to decision-making
aids for times of related emergencies.
Titans awake
The prevailing volcanic hazards were
defined and assessed with the aim of
devising protection strategies for the
human populations under threat. Characterizations were conducted on volcanoes considered as active, taken to
be those that had entered into eruptive
activity since the Pre-Columbian era,
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about 1 000 years B.P. These included
determination of the frequency, intensity and also the style2 of their eruptions.
CONTACTS :
The risk in fact varies with the eruption
style: explosive eruptions, accompaJean-Luc LE PENNEC
nied by nuées ardentes, are more danet Pablo SAMANIEGO,
gerous than effusive ones, where lava
flows are produced.
chercheurs à l’IRD
The research team also identified doLaboratoire
zens of other volcanoes having the
Magmas & Volcans
(UMR IRD/Univ. Blaise Pascal/ potential for reviving their activity. Studies were consequently made on their
CNRS)
development, their periods of activity
Address:
were dated and the changes and deveUniversité Blaise Pascal
lopments undergone by their magmas
5, rue Kessler
determined. The search is continuing,
63038 Clermont-Ferrand
to gain information and understanding
Tél : +33 (0)4 73 34 67 53
of how magma chemistry, which varies
enormously with time but also with the
jean-luc.le-pennec@ird.fr
location of the volcanoes, influences
pablo.samaniego@ird.fr
eruption onset and processes.
Two mountain chains, two types of
volcano
REFERENCES :
The considerable mass of data gathered helped classify the Ecuadorian
Johnson J.-B., Samaniego
volcanoes according to their morphoP., Hall M.-L., Le Pennec J.logical characteristics, the chemistry
L., Eissen J.-P. Recent and
of their rocks and their eruptive style.
Active Volcanism in the
Significant differences between the volEcuadorian Andes. Journal
of Volcanology and Geother- canoes of the two cordilleras appeared.
mal Research, special issue, The western chain, where Pichincha
2008
stands, among others, constitutes
the volcanic front facing the Pacific.
Eruptions there are characterized by
KEY WORDS :
ash falls which cover 1 000 to several
Ecuador, volcano, hazard,
hundred thousand km2 and therefore
Andes
strongly affect the people living around
them.
On the other side of the inter-Andean
valley, activity has been even more intense over the past 10 000 years. The
eastern cordillera bears the large stratovolcanoes, composite cones built up
by the accumulation of lava flows, rock
debris and ash, like Cotopaxi or Tungurahua. These volcanoes range from
15 to 20 km in diameter at their base
and rise up to 3 to 4 km high. Periodically they produce nuées ardentes that
can travel as far as 50 km, down towards the valleys. These eruptions are
accompanied by falls of ash and rock
fragments which are also carried, by
the prevailing east winds, towards the
inter-Andean valley and its many cities.
The Andean regions of Ecuador therefore live under the menacing fire
of its large crop of volcanoes. This
configuration is almost unique in
the world, where the hazard is accentuated by population growth and
urbanization in the inter-Andean valley. The work of IG-EPN and IRD −hazard definition, mapping of volcanic hazards, close surveillance− is revealing
ways to develop improved protection
measures for the inhabitants when
crises arise, as was the case in 2006
during the last eruption event of Tungurahua where the warning issued by
scientists allowed people to be evacuated in time.
Redaction DIC - Gaëlle Courcoux
Translation - Nicholas Flay
1. Instituto Geofisico, Escuela Politécnica
Nacional (IG-EPN), Quito.
PRESS OFFICE :
INDIGO,
IRD PHOTO LIBRARY :
Daina Rechner
+33 (0)4 91 99 94 81
indigo@ird.fr
www.ird.fr/indigo
The roof of the church in Bilbao, Ecuador, collapsed under the weight of ash, a consequence of the
eruption of Tungurahua in August 2006
Gaëlle Courcoux, coordinator
Délégation à l’information et à la communication
Tél. : +33 (0)4 91 99 94 90 - fax : +33 (0)4 91 99 92 28 - fichesactu@ird.fr
©IRD / Yvan Repetto
2. The style characterizes the eruption: it
can be explosive with various degrees of
intensity, or effusive, etc.
Vincent Coronini
+33 (0)4 91 99 94 87
presse@ird.fr
©IRD / Yvan Repetto
Scientific bulletin 321- June 2009
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