Mexico's Popocatepetl volcano releases gas into the atmosphere, as Mexican authorities raise the alert level.
by Simon Hanna
by Mohammad Hamid
by Tara Cleary
by Irene Klotz
by Rob Muir
by Tarek Amara
by Steve Olafson
by Jim Forsyth
by Martin Hutchinson
by Gopal Sharma
by Staff Reporter
