A volcano some 60 kilometres from Mexico City has been throwing out ash and hot, glowing chunks of rock since 12–13 April.

This activity isn’t particularly unusual — Popocatépetl (whose name comes from the Aztec for ‘smoking mountain’) is one of Mexico’s most active volcanoes. In 1994 it started belching again after more than 50 years of relative quiet, erupting in 1996 and 2000. The 2000 eruption was accompanied by an evacuation of 50,000 people.

“There’s not a huge danger from the present activity as it is,” says James Gardner, a volcanologist at the University of Texas at Austin, who has worked on the volcano. “But there’s good reason to keep an eye on this one.” Even small explosions can send out ash that, if the wind is right, can close Mexico City’s international airport, Gardner says. And the volcano, along with its ice cap, is capable of producing massive lahars or mud flows. The last serious eruption was 500 years ago, he says. A hazard risk map produced in 2001 by Mexican and US researchers shows that such flows could hit populated areas, but definitely not Mexico City (see here for full-size map. The blue areas are cities and towns; red and yellow are flood zones of different severity).

There is “good, capable” scientific monitoring of this volcano to keep people informed of the risk, says Gardner. Popocatépetl Volcanological Observatory was luckily founded in 1994, just a few months before it started rumbling. This includes some 15 remote field stations around the volcano, with seismometers, tiltmeters, and video cameras for real-time monitoring.

For now, local officials at the Mexican National Centre of Disaster Prevention have put out a yellow alert (their third-highest warning) for the volcano, which has about 500,000 people living in its vicinity. People are being asked to stay at least 12 kilometres away. Locals in towns where the ash is falling, including Puebla, are being told to cover their mouths and clean debris from weak rooftops to avoid building collapse.

You can find updates on global volcanic activity, including this one, through the Global Volcanism Program.

Photo: AP/Press Association Images, Map: National University of Mexico (UNAM), University at Buffalo