Moi, Paul Derand

Moi, Paul Derand

Mexico's most dangerous volcanoes

These are all Mexican volcanoes that have erupted in the last 500 years, that have a Volcanic Activity Index (VAI) of at least 0, and that have the potenital to threaten several thousands of people or more in an eruption. They are classified by their dangerosity (depending of the VAI and the number of people eventually threatened): class 0 is very little to little, class 1 is a little to moderate, class 2 is dangerous to very dangerous, class 3 is very dangerous, class 4 is extremely dangerous. Values superior to 4 can be used if necessary.

 

Ceboruco (class 0,3):

Ceboruco is a  vulcanian (VEImax=3) volcano located in Western Mexico. However, it is also capable of producing significant lava flows, that's why it has a EVImax (maximal eruption volume index) of 5/8

A typical significant eruption for this volcano would be similar the 1870-1875 eruption. This eruption was vulcanian, but explosive activity was accompannied by extrusion of a large volume of lava, forming a 1,1 cubic km lava flow that reached the lower western flank.

Even though this volcano is capable of erupting large volumes in its eruptions, it has a VAI of only 1,14 (moderate) because its eruptions are rather infrequent.

The places most likely to be affected by an eruption would be located on the lower flanks, to the North and the West of the volcano because there is a  4 km wide summit caldera breached to the NW. El Marquesado, Uzeta and Tetitlan are the villages located in this area, their populations only sum up to a few thousand people.

 

Colima (dangerosity 1.9):

Colima is a plinian (VEImax=5) volcano located in western Mexico. It has a VAI of 1,85, this is moderate to high, this means it can have frequent and powerful eruptions. There have been frequent historical eruptions from the summit crater. Pyroclastic flows, vertical ash columns and lava flows are characteristic of eruptions at the volcano.

A plinian eruption from Colima volcano would seriously affect the city of the same name (132K inhabitants) with moderate ashfall as the city is located only 30 km to the south of the volcano. It would also affect, with the same dangers, other smaller towns located on the lower flanks of the volcano: Atenquique, Comala, Coquimatlan, San Marcos, Tonila, Cuauhtémoc, Suchitlan, El Chivato, San Antonio. The total affected population by ashfall from a plinian eruption would be 177K people. Moreover, pyroclastic flows may reach 12 km long, threatening 11,3K people. The latest eruption of that intensity from Colima was in 1913.

A sub-plinian (VEI=4) eruption would affect only Atenquique, Coquimatlan, San Marcos, Tonila, Suchitlan, El Chivato, San Antonio with moderate ashfalll, this makes a total of 18K threatened inhabitants and  less than a thousand people threatened by pyroclatic flows. Eruptions of this intensity have occured at many times during the historical period.

 

Michoacán-Guanajuato (dangerosity 4.5 to 4,0):

Michoacan-Guanajuato is a monogenetic volcanic field. This means that it is a volcanic field that always erupts at a different location: a vent never erupts twice. So we have more than a thousand distinct Holocene vents in a 100 km radius.

It has a VAI of 1,61, which is moderate.

You may think you have never heard about this volcanic field but I'll tell you that it erupted twice in history, once at Jorullo, and that the other eruption was more famous: it was the Paricutin eruption!

Actually, the Paricutin represents the typical eruptive style of this volcanic field. The Paricutin eruption was VEI=4, it corresponds to the VEImax of this volcanic field. Moreover, there are the same sort of risks: lava flows and ashfall. El Jorullo produced a more violent type of strombolian activity.

Due to the wide perimeter where eruptive centers might occur, a vast zone may be affected by eruptions. The major settlements in this area are Los Reyes, Apatzingan, Nueva Italia, Ario de Rosales, Patzcuar, Uruapan, Zacapu, Antunez, Buenos Aires, Lombardia, Cheran and Paracho. Their populations sum up to 734K inhabitants. 64% of the dangerosity here (4,4) is based on the important (even though is is'nt dense) population located in this vast area. ONE eruption  from Michoacan-Guanajuato will never threaten 734K people at once. The maximum population threatened would be 315K people if the eruptive center was less than 7,5 kilometers from Uruapan. In this case we shall adjust the dangerosity to 4,0.

 

Popocatépetl (dangerosity 5.1):

Popocatepetl is a plinian (VEImax=5) volcano located between the two very populated metropolitan areas of Puebla and Mexico. It has frequent mild to moderate eruptions, with infrequent plinian eruptions at intervals of a few hundred years ; that's why it has a VAI of 1,89 (moderate).

In the last 23,000 years, there have been at least 7 Plinian eruptions from Popocatépetl. Prehistoric and historic plinian eruptions repeatedly formed large volumes of hot pyroclastic flows and air falls that extended 20 km southeastwards and 10 to 15 km northeastwards. See here the risk maps of this volcano.

Moreover, there are a series of faults around the volcano, and one of those faults makes the southeastern flank of the edifice unstable. In case of a Mt St Helens style eruption, with lateral blast and debris avalanche to the SE, it could be enormous! Popocatepetl’s debris avalanche 23,000 years ago traveled as far as 70 km southeast of the summit, and totaled a volume of roughly 30 cubic kilometers of material, more than 10 times the size of St. Helen’s 1980 landslide eruption.

With no doubt, this volcano could affect more than 509K people from Amecameca, Atautla, Tepetlixpa, Ecatzingo, Ocuituco, Tetela del Volcan, Huaquechula, Santa Ana, Atlixco, Chalchihuapan, Cholula and San Andrés Calpan, with pyroclastic flows and/or flank collapse in case of a large eruption. Luckily, these sort of strong eruptions with slope failures are very unlikely to happen frequently.

However, even during mild to moderate eruptions, ashfall remains a big problem. There would be ashfall in a 1333 km radius in case of a plinian eruption, in a 375 km radius in case of a sub-plinian eruption, in a 110 km radius in a vulcanian eruption and in a 30 km radius in a strombolian eruption. So we can say that Puebla aiport may have problems even in a strombolian episode, that Mexico city may be affected even by a vulcanian eruption, that a sub-plinian eruption is capable of sending ash as far as Chiapas, Veracruz, Queretaro, Guanajuato, Michoacan and Guerrero and that a plinian eruption could send ash as far as Guatemala, Yucatan, Baja California del Sur and Texas.

 

Pico de Orizaba (dangerosity 3.0):

Pico de Orizaba is a plinian (VEImax=5) volcano located in eastcentral Mexico. It has a VAI of 1,17, which is moderate to low because its eruptions are quite infrequent.

The volcano is capped by a glacier, this is why lahars are a significant threat. The volcano has had ash-producing eruptions in historical times. Lava flows have also occured in historical times, but luckily, because of their composition they are too viscous to reach inhabited areas. Pyroclastic flows would also be a minor threat as they could flow a maximum of 10 km, not more, so that it would not reach inhabited areas..

As I said above, lahars are the main threat. They could threaten up to 364K people living in Tlachicucha, Ciudad Serdan, Esperanza, Maltrata, Ciudad Mendoz, Rio Blanco, Ixhuatlacillo, Palmira, Orizaba, Ixtaczoquitlan, Cuiyapacha, Teletzingo, La Cienaga, Xometla, Xuchi, Texmola, Paso Carretas, Atzitintla and San Miguel Zoapan.

Moreover, ashfall coud be felt at several hundred kilometers in a plinian eruption, as far as hundred kilometers in a sub-plinian eruption, in a 45 km radius for a vulcanian eruption and a 20 km radius for a strombolian eruption. This means Orizaba and Cordoba could be affected by ashfall even during a vulcanian eruption, and that a sub-plinian eruption might send ash as far as Puebla and Heroica Veracruz.

Finally, the volcano is steep-sided and edifice collapse has occured some times during the volcano's life. An edifice collapse would send a debris avalanche as far as 20 to 30 km, threatening hundreds of thousands of people from Tlachicucha, Ciudad Serdan, Cuiyapacha, Teletzingo, La Cienaga, Xometla, Xuchi, Texmola, Paso Carretas, Atzitintla and San Miguel Zoapan, and possibly  Maltrata, Ciudad Mendoz, Rio Blanco, Ixhuatlacillo, Palmira, Orizaba and Ixtaczoquitlan. Luckily, edifice collapse is rare.

 

El Chichon (dangerosity 0,9):

El Chichon is a plinian (VEImax=5) volcano located in southeastern Mexico.

El Chichon had a plinian eruption in 1982, it triggered widespread ashfall and acid rain reduced agricultural potential in this area. Chiapas is one of the poorest states of Mexico, lots of people depend on agriculture. An acid rain can significantly affect agricultural products during one year or so. Moreover, ashfall could destroy precarious houses in the area. In the 1982 plinian eruption, pyroclastic flows travelled 8 km from the volcano.

Luckily, its eruption are infrequent and it has a VAI of 1,17.

 

Tacana (dangerosity 1,6):

Tacana is a sub-plinian (VEImax=4) stratovolcano located in the border between Guatemala and Mexico.

It has a crater lake and mild phreatic eruptions took place in historical times.

Its most powerful known explosive activity occurred at about 70 AD (± 100 years), it had a VEI of 4 and produced pyroclastic flows.

The agricultural valley at its NNE foothills is covered with thick deposits of lahars. From its headwaters in Guatemala, the valley (Rio Coatan) drains through Mexico to the Pacific Ocean. In case of a pélean eruption with associated lahars, the volcano could threaten more than 250K people.

Luckily, the volcano's VAI is only 0,65 (little).



22/02/2015
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