Amber L. Madden-Nadeau


Popocatepetl – more colloquially known as “Popo” – means “smoking mountain” and is an active volcano just 60 km from Mexico City (Figure 1) with 20 million people living within this catchment area. It stands right next to Iztaccihuatl or “Izta”, an extinct volcano with multiple peaks. Iztaccihuatl means “white woman”, with many believing that this volcano looks like a sleeping woman. At 5636m and 5230m, Popo and Izta are the second and third highest peaks in Mexico, respectively.

Figure 1: Popocatepetl as seen from Mexico City.

These volcanoes share a well-known story in Aztec mythology, whereby they were deeply in love. Popo was a young warrior and Izta a beautiful princess. Izta’s father demanded that, before Popo was allowed to marry Itza, he must first go to war for his tribe. Popo sets off for battle immediately, with Itza waiting for his return. However, a rival sends word that Popo died, when in reality he was victorious in his fight against his enemies. When Itza hears this false news, she is full of sorrow and dies of a broken heart. Popo returns triumphant, discovers his beloved, and is inconsolable. He carries her into the mountains to build a funeral pyre for them both. The Gods, touched by their story, turn them into mountains so that they can finally be together. The legend goes that Popo watches over the sleeping Itza to this day, as shown in Figure 2, and spews ash once in a while to remind everyone that he will always continue to do so.

Figure 2: An artist’s impression of Itzu and Popo, stood in front of their respective volcanoes.

So now we can get back to the science. Popo in the past has produced highly explosive plinian-style eruptions. Plinian eruptions are characterised by eruption columns of volcanic gas and ash extending high into the atmosphere. Where the density of this gas-ash mixture becomes equal to that of the surrounding atmosphere, an umbrella cloud forms (Figure 3). Plinian eruptions lead to the ejection of large amounts of pumice and often produce Pyroclastic Density Currents (PDCs). These consist of hot ash and volcanic gases, and travel down the flanks of the volcano, closely following the surface of the land. They can reach temperatures of 1000oC, can travel up to 700km/hr, and cannot be out-run making them a major volcanic hazard that leaves death and destruction in their wake.

Figure 3: Schematic of an eruption column.

The most explosive eruption to have occurred at Popo happened approximately 14,000 years ago and is called The Pumice with Andesite (PwA) eruption; it would have covered Mexico City in ash. Figure 4 is a map of the region, showing isopachs where 10cm and 15cm of ash fell. The injection of a new batch of magma into Popo’s magma chamber is thought to have triggered this eruption, as it adds extra volatile components (Sosa-Ceballos et al. 2012). Mixed pumice, whereby it is possible to see mingling patterns between two different magmas of different colours and compositions, can be an indication of this process. This magma mixing process may be part of the reason Popo still spews ash in anguish, while Itza lies extinct beside him.

Figure 4: Map showing Popocatépetl and the major cities and towns within its vicinity. The 15 and 10 isopachs for the PwA Plinian fallout are shown. Insert map gives this regional context showing the Trans Mexican Volcanic Belt. F.Z. = fracture zone and EPR = East Pacific Rise (Figure modified from Sosa-Ceballos et al. 2012; Arana-Salinas et al. 2010; Siebe & Marcías 2006 by the author)

Additional reading

Arana-Salinas, L., Siebe, C. & Marcías, J.L. 2010. Dynamics of the ca. 4865 yr 14C BP “Ochre Pumice” Plinian eruption of Popocatépetl volcano, Mexico. Journal of Volcanology and Geothermal Research, 192, 212-231.

Siebe, C. & Marcías, J.L. 2006. Volcanic hazards in the Mexico City metropolitan area from eruptions at Popocatépetl., Nevada de Toluca, and Jocotitlan stratovolcanoes and monogenetic scoria cones in the Sierra Chichinautzin Volcanic Field. In: Siebe, C., Marcías, J.L. & Aguirre, G. (eds.). Neogene-Quaternary Continental Margin Volcanism: A Perspective from Mexico. Geological Society of America, Special Publication, 402, 253-329.

Sosa-Ceballos, G., Gardner, J.E., Siebe, C. & Marcías, J.L. 2012. A caldera-forming eruption ~14,100 14C yr BP at Popocatépetl volcano, Mexico: Insights from eruption dynamics and magma mixing. Journal of Volcanology and Geothermal Research, 213, 27-40.

Sparks, R. S. J., Wilson, L. & Hulme, G. 1978. Theoretical modeling of the generation, movement, and emplacement of pyroclastic flows by column collapse. Journal of Geophysical Research: Solid Earth, 83, 1727-1739.

Walker, G.P.L. 1981. Plinian eruptions and their products. Bulletin of Volcanology, 44, 223-240.

 


“I am  a volcanologist and igneous petrologist in the first year of my DPhil in the Department of Earth Sciences studying controls on eruptive style using Krakatau Volcano, Indonesia as a case study.”

 

Advertisements