News reports from Mexico indicate increasing levels of activity at the Popocatépetl volcano near Mexico City after the alert was raised to yellow (level 3) on 12 May. At 5,426 metres, Popocatépetl (the name is derived from the Aztec for ‘smoking mountain’) is North America’s second highest volcano, though it is dwarfed by many of the 6,000+ metre volcanoes in the Andes.
Popocatépetl: The Current Eruption
Low levels of gas and steam emissions from Popocatépetl have been regularly recorded over the past months in the Smithsonian Institute’s Global Volcanism Program reports. On 12 May, however, a number of gas emissions and moderate explosion led to Mexico’s national disaster prevention agency, CENAPRED, raising the level of alert. The agency reported that the observed levels of activity had in the past been the precursor to ash falls, magmatic eruptions, and hot debris avalanches known as pyroclastic flows.
Access to the volcano was restricted within a radius of 12km of the crater itself: roads were closed and the population warned to be alert for further information. Popocatépetl lies within a densely populated area less than 70km from the centre of Mexico City, which is home to over 8.5 million people.
Mexico’s Volcano – Past Eruptions
Popocatepétl is a notoriously explosive volcano. Prior to the most recent phase of eruptions, geologists have used various techniques to identify and date at least 46 separate eruptions going back many thousands of years. A notable series of eruptions occurred in the middle ages, with almost twenty separate eruptions identified between 1488 and the end of the 17th century: There was a subsequent lull until activity resumed in the late 20th century.
These eruptions have varied in nature, but are characteristically explosive (cooler magma reaches the surface and explodes) rather than effusive (hot magma reaches the surface, gases dissipate), although the highest recent rating on the volcanic explosivity index (VEI) is 3, which is ‘severe’ (the 8-point scale goes as far as ‘mega-colossal’) but in its earlier history, this volcano is thought to have produced at least three highly explosive plinian (on the scale of Mt. Vesuvius) eruptions (at least 4 on the VEI).
Previous eruptions have been accompanied by damaging geological phenomena including lahars (mud flows caused by the melting of glacier ice and its catastrophic down-rushing through ash and soil) and pyroclastic flows. Although detailed statistics are unavailable, previous eruptions have caused damage and loss of life.
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