A close up view of the most destructive recent volcanic eruptions around the world.

The earth really moves in this episode as we take in scenes and stories from some of the most devastating of all the natural cataclysms: the earthquake. With all its pent-up power, nothing releases more sheer destructive energy than the grinding forces at work between the Earth's tectonic plates.

Things get personal in this episode as we really get under the skin to explore something that is a threat to all of us wherever we live: the epidemic and its global big brother, the pandemic.

Flash floods in Brazil, the deluge that followed Hurricane Katrina, and the overflow after the Indian Ocean Tsunami of 2015 are all, to some extent, natural phenomena. But is a changing climate making them not only more likely but their impact more severe?

Ours is a dangerous world where geological mishaps—avalanches, landslides, heat waves, sinkholes and blizzards—can spell disaster almost as much as big cataclysms like earthquakes and tidal waves. While casualty counts might be lower, geological disturbances still cause their fair share of misery.

Our focus for this chilling but fascinating episode is when humans are a serious danger to themselves through nuclear and industrial accidents. We'll look at the Fukushima and Chernobyl nuclear disasters, the Bhopal gas accident, the Savar Plaza building collapse and the BP oil spill.