Less than 40 miles outside of Mexico City, the volcano Popocatépetl is erupting, sending ash plumes roughly two miles into the atmosphere. Over the weekend, airlines took the precaution of cancelling flights out of Mexico City, even though the airport itself remained open.
This means that the eruption at the volcano has moved from sporadic explosions (Phase II) to frequent small to intermediate explosions, usually caused by a dome collapse (that can generate pyroclastic flows). Tremor is almost constant at the volcano, along with constant emission of ash-and-steam from the summit vent.
Pyroclastic flows are extremely dangerous. Composed of a toxic stew of gases, ash and bits of solid and molten rock, they move like an avalanche down the side of a volcano, moving at speeds of over 60 miles an hour, way faster than any human can run.
Pyroclastic flows occurred during the eruption of two of the larger volcanic events of the 20th century, Mt. St. Helen’s and Mt. Pinotubo. Like those two volcanoes, Popocatépetl is a stratovolcano, a type of volcano known for its explosive eruptions.
It has a long history of eruptions, dating back to the Aztec times. It took a brief 50-year nap from 1944 through the early 1990s, but has since been erupting fairly regularly. On Sunday, scientists noticed that a lava dome about 820 feet across had grown in the middle of the crater at the top of the mountain.
Popocatépetl has been erupting for over a month now and reached the classification “Yellow Phase 3″ once before in May, before being downgraded in June. With roughly 25 million people living in the region around the volcano, the Mexican Government is keeping an eye on this one.
If you want to start your own volcano-watch, Mexico’s CENAPRED (Centro Nacional de Prevención de Desastres) has cameras pointed at the summit in four locations: Tochimilco, Tianguismanalco, Altzomoni, Tlamacas. The images update every minute.
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