Volcanologist Tom Pfeiffer leads an expedition to some of Indonesia's most remote and rarely visited volcanoes.

Mexico City is one of the most densely populated places on earth. Its twenty million inhabitants are constantly living with the threat of Popocatple, an active volcano that can destroy the city at any time.

In Indonesia, the air is 40 times above safe levels for humans and sulphuric acid vents from the ground in dense, yellow clouds; small volcanoes are reported to erupt every 15 minutes.

Japan is going through a seismic crisis after the devastating Tsunami of 2011. We look closely at two very dangerous volcanoes, both are considered to be in the top 5 most dangerous on the planet.

For people who live on active volcanoes, life has an element of impermanence to it. There is always the fear that one day their turn will come, and their home will be in the path of the volcano.