World Federation of Scientists. Erice International Seminars on Planetary Emergencies - 44rd Session.
Limits to Development PMP. “Ettore Marjorana” Centre for Scientific Culture, Erice, 19-25 August, 2012
ENDANGERED SUSTAINABILITY OF A MEGALOPOLITAN REGION: THE UNEXTINCTED ACTIVITY
OF THE POPOCATEPETL VOLCANO, MEXICO.
ALBERTO GONZÁLEZ POZO
Theory and Analysis Department
Universidad Autónoma Metropolitana-Xochimilco, MÉXICO
The notion of sustainability has been described mostly as a critical influence of human activities trying to
extract and transform natural resources beyond a limit that does not assure their availability for later
generations. But announced or unexpected natural hazards like earthquakes, or impacts of cosmic objects
(two issues already shown in the Erice Seminars during the last decade) may have similar, even worse
consequences. That is the case of the unextincted Popocatepetl volcano, because it arises in the middle of
several converging metropolitan areas that form together a greater megalopolis in the highlands of Central
Mexico.
4 Metropolitan regions around the Popocatepetl volcano in Mexico form a Megalopolis of 24.3 million inhabitants.
The circles describe risk areas discussed in this article. (Sources: PUEM-UAM, 2000, Macías Vázquez et al.,1995 and INEGI, 2000)
I have shown in other seminars the spectacular growing of the urbanized giant that arose from Mexico
City, with less than half a million inhabitants starting the XXth Century and reached more than 20 million
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to the closing of the same period, swallowing ancient towns and villages around it. (González Pozo, 2000
and 2003) As it continues to grow, and as in other neighboring valleys with their own central cities
happens the same, it gives an good example of a diminishing urban sustainability, not only because of the
serious practical problems these giant settlements have, related to the provision of drinkable water, or the
disposal and evacuation of rainwater (because one of the metropolises is a closed basin), or the increasing
traffic and air-pollution problems, but also because of the latent danger to human lives and assets
potentially exposed to a great eruption of a volcano.
Eastern limit of the Valley of Mexico with the Iztaccihuatl and the Popocatepetl volcanoes (Googlearth).
This presentation gives some facts about the present situation, as well as the measures taken to face and
mitigate the threat of a sudden increase of the risk level.
A COUNTRY DIVIDED BY A VOLCANIC BELT
Volcanic activity seems to coincide with border regions between continental or oceanic plates, and
Mexico is no exception. But when one sees more closely the distribution of active volcanoes in our
region, it is clear that most of them are in a band along the 19°N latitude that crosses the whole Country
from the Pacific Ocean to the Gulf of Mexico. It is called the “Trans-Mexican Volcanic Belt” (also
neovolcanic axis) and was probably formed between Pleistocene and Holocene times. (Santoyo Villa et
al. 2005) The Popocatepetl volcano occupies there a central position, next to the biggest human
agglomeration of the Mexican central high plateau.
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“Trans-Mexican Volcanic Belt”. Mexico City and the Popocatepetl volcano are in the middle (Source:Instituto de Geofísica, UNAM)
The fact that the giant Stratovolcano (5,452 m. over sea level) is active since long ago explains its ancient
Aztec name. Popocatepetl means “smoking mountain”, and the inhabitants of the Mexican capital
consider it and its neighbor, the Iztaccihuatl (in Aztec “sleeping lady”, 5,285 m), as important and typical
features of the surrounding landscape that had been permanently covered by heavy snowcaps, thick
enough to supply important amounts of freshwater to the surrounding valleys.
Two snow giants: Popocatepetl seen from Iztaccihuatl, ca. 1960 (Photo: Virgilio Gonzalez Pozo)
But since the last 15 years, two remarkable changes have gradually taken place: the first one was the
unusual awakening of eruptive activity inside the crater of the Popocatepetl, followed by sudden
explosions throwing outside solid fragments or exhaling giant “plumes” or columns of smoke with gases
and volcanic ashes; and the second one is that the once called “permanent” snowcaps have gradually
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disappeared, due to the climatic changes that affect now the whole world. Depending on the climatic
conditions, those and other Stratovolcanoes in Mexico may recover their snowcaps for several weeks or
months, but most of the year show a dry image in the landscape.
Left: Thermographic infrared image of a strong smoke column after a crater explosion, 2000 (Source, CENAPRED,2000)
Right: Big smoke column in daylight. In foreground: a colonial church on the top of a pyramid. (Source, Cronica Digital, 2012), México)
Depending on the height of the plume (up to 8 kilometers) and the prevailing winds (especially those
from east to west or the opposite) the ashes are deposited in the surrounding territory, traveling distances
of 10 to 50 kilometers. Until now, the ashes are a minor disturb even if the city cars suddenly are covered
by a thin layer of a fine and abrasive powder. But sometimes, their presence is heavy enough to stop for
several hours or some days the aircraft activity in the International Airport of Mexico City.
Types and effects of volcanic emissions
(Translated after Reyna de la Cruz, 2004)
Material
expelled
Associated
risk
Speed
Distance
range
More frequent
consequence
Liquid lava
Lava flows
Low
Short
Ground
destruction
Ashes
Rain of
ashes
Medium
Intermediate
Ashes
accumulation
Very high
Short to
Devastation
intermediate
Medium
Long to
very long
Mud (fragments Mud flow
and wáter)
(lahar)
Medium
to high
Intermediate
Devastation
to long
Ground slipping Rubble
or falling
avalanche
Hign to
Intermediate
Devastation
very high to long
Several types of Pyroclastic
fragmens
flows
Ashes
Rain of
ashes
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Ashes
accumulation,
sewage
blockage
The fear under such new situation is now present, but only in the population of small villages and hamlets
next to the volcano. They are aware that if the hazard is strong enough they will be compelled to evacuate
their homes for security reasons.
THE LONG RECORD OF VIOLENT EPISODES OF A SEEMINGLY HARMLESS GIANT.
The oscillations between weak and strong activity periods in the Popocatepetl since 1994 is only a
warning sign that the volcano is reawakening. Today, we know better its long history, where violent
eruptions took place between lapses of some centuries or some millennia of calm. In strong eruptions, the
volcano expelled flows of lava or volcanic mud that contributed to build its typical conic shape by
successive layers. But it could also throw pyroclasts (rocks or smaller fragments) that covered larger
areas. Finally, crater explosions could expel giant smoke columns already described.
SHORT ERUPTIVE HISTORY OF THE POPOCATEPETL VOLCANO, MEXICO
(Shortened, after CENAPRED)
Between 23,000-14,000
years before present
At least two large Plinian eruptions, one of them, St. Helens-type, destroys previous
volcanic edifice.
Between 14,000 years before present and 800 A.C.
Seven large eruptions and several minor eruptions. In the first Cent. B.C., another
small volcano called Xitle in the southern part of the Valley of Mexico, covers with
lava the ancient pre-columbian town of Cuicuilco, rediscovered in the first half of the
XXth. Century after hard excavation in the rocky lava.
800 A.C. to 1927 A.C.
About 1200 years, with at least 17 moderate or mild eruptions.Most of them produce
ash and pumice emissions that fall at different distances (some reach 40 and 50
kilometers away from the crater) and form soil layers between few to 30 centimeters
thick. All these episodes restart fumarolic activity. Some of them are historically
recorded and described.
1927
Moderate eruption. Besides episodic explosions inside the crater that produce ash
and pumice emissions, a small lava dome grows in the crater floor. Several people
die inside the crater during sulphur extraction works.The next six decades the
volcano seems to rest, with remnants of fumarolic activity and is covered by
permanent icecaps, as it was since ancient times.
1994-1997-2001
Moderate eruptions. Episodic explosions produce ash and pumice emissions. A
small lava dome grows on the crater floor and fills up to 20% of the crater capacity.
5 people were killed close to the crater rim during an explosion in May, 1995. The
former icecaps start to disappear.
2001-2012
Moderate eruptions, some produce very high smoke columns, up to 8 kilometers
height, that carry volcanic sand (silica and pumice). One of them causes the closing
of the International Airport of Mexico City. The presence of icecaps is rather rare.
They return but melt again after several months or weeks.
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Left: Nocturnal explosion inside the crater, 2000. Pyroclastic material runs down outside and gasses and ashes mix with the atmosphere.
Right: Interior view of the crater in a “resting” period before 1994. (Sources: Instituto de Geofísica, UNAM and H. Delgado, UNAM)
RENEWED CONSCIENCE OF THE VOLCANIC RISK AND THE MITIGATION PROVISIONS
The recent reawakening of the Popocatepetl is now closely followed by experts and the media, thus
creating a renewed conscience of the risk and the vulnerability of the whole involved region. The creation
of a Federal Government Agency specialized in disasters, the National Centre for Disasters Prevention
(CENAPRED for Centro Nacional de Prevención de Desastres) within the Secretary of Government,
which has the highest rank among the Cabinet. Its physical location within the main Campus of the
National Autonomous University of Mexico (UNAM), allows a close relationship with research experts
of several convergent disciplines like geophysicists and vulcanologists, engineers, planners and social
scientists. Local governments of the three Federal States involved, as well as city authorities of the most
important or smaller urban settlements (especially those closer to the Stratovolcano), also watch the
volcano’s behavior.
A
B
C
Three different risk maps related to the Popocatepetl hazards: (Source: Macìas Vázquez et al., 1995. Instituto de Geofísica, UNAM)
A. Describes possible falls of volcanic fragments in erupptions of three intensities between a radius of 28 Km;
B. Irregular area where lava and volcanic mud could flow over slopes and river-beds, with maximum distances of – and ---Km respectively;
C Possible falls of ashes in a broader area with maximum radius of 50 Km that reach Mexico City. Dotted line shows the area covered in a
Plinian eruption . The central area between diagonals represents predominant wind directions either east-west or the opposite.
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With their participation, several maps have been produced showing the hazard areas for different
situations. One of them shows the possible fall of tephra (pyroclastic material) around the mountain
flanks. Other the superficial flow of lava or hot volcanic mud, that quickly descend following the gorges
and topographical valleys. Other, more ominous, considers the case of violent explosive eruptions,
showing the fall of ashes and volcanic sand once the prevailing winds disperses them from the big smoke
plumes and transport them to short or long distances depending from the violence of the explosions, some
of them reaching the Metropolitan Areas around the volcano.
The menacing giant is now surrounded by sensors and recording devices that follow constantly its
behavior, forming a network that alerts the scientists and eventually triggers a sort of volcanic “traffic
light” put in public and visible places within a distance of ca. 10 km of the volcano crater, where the
green light means that the volcano is resting, the yellow light indicates some activity and the need to
watch constantly the news and prepare for an eventual evacuation, and the red light the imminent
evacuation measures and the movement to provisional shelters.
The volcano is constantly watched with different monitoring devices from several places. (Source, CENAPRED-UNAM, 2002 and 1991)
Up to now, the mitigation measures are concentrated upon the most vulnerable settlements within the
smaller area of 14 Km of radius, but this does not exclude the possibility of another strong or violent
eruption that may cause damages in a much broader area of 50 Km radius.
And meanwhile, the megalopolitan region continues to expand in each of the four metropolitan areas
around the volcano, approaching slowly but continuously their urbanized zones to the smoking colossus.
This of course, represents a crucial question to its future sustainability.
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SOURCES:
CENAPRED, in http://cenapred.gob.mx/es/Instrumentacion/InstVolcanica/MVolcan/HistoriaVolcan
Delgado, H. in http://earth-of-fire.over-blog.com/article-les-volcans-mexicains-tmvb-le-popocatepetl75508714.html
Espíndola, Juan Manuel and Macías Vázquez, José Luis (1996), “El vulcanismo”, CIENCIAS, 41, January-March
1996, UNAM.
González Pozo, Alberto (2000), “Water use, abuse and waste: limits to sustainable development in the Metropolitan
Area of Mexico City”, in International Seminar on Nuclear War and Planetary Emergencies, 25th. Session,
Singapore.
_____________, (2003) “Urban Mobility in the Mexican Metropolis” in International Seminar on Nuclear War
and Planetary Emergencies, 30th. Session, Singapore.
Macías Vázquez, José Luis et al., (1995), Mapa de Peligros del Volcán Popocatépetl INSTITUTO DE
GEOFÍSICA, UNAM-CENAPRED , June1995
Reyna de la Cruz, Servando (2004), Volcanes, Peligro y Riesgo Volcánico en México, Serie Fascículos,
CENAPRED, México.
Santoyo Villa E., Obando Shelley, E., Mooser, F. and Leon Plata, E. (2005), Síntesis Geotecnica de la Cuenca del
Valle de México, TGC, México.
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