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Schools and public parks have been closed in central Mexico, as the volcano Popocatépetl spews out ash, smoke and incandescent rock. Huge swathes of the country were carpeted in grey ash as three million local people were advised to prepare for evacuation. Situated 43 miles southeast of Mexico City, and with 25 million people living within a 60-mile radius, Popocatépetl is considered one of the most dangerous volcanoes in the world. On 21 May, Mexico’s National Centre for Prevention of Disasters raised the alert level to Phase 3, one step below an evacuation order. At this level, volcanoes may produce mild to moderate explosions that can hurl fragments of rock. It may even expel magma. At a news conference the next day civil defence coordinator Laura Velázquez said there was “no risk to…