Lava and volcanic debris have built more than 80 percent of Earth's surface over millions of years, and the planet's roughly 1,500 active volcanoes still kill an average of 800 people a year while threatening some 500 million more who live in their shadow. This Spark documentary follows scientists trying to get ahead of that death toll, tracking how magma forces its way upward through fractured rock from as deep as a hundred miles below ground before it ever reaches a crater. Volcanologists explain what current monitoring can and cannot tell them, from seismic tremors to gas emissions and ground deformation, and where those signals have failed to give enough warning in the past. The film treats prediction as an unsolved engineering and geology problem rather than a settled science, weighing what separates a volcano's routine grumbling from the buildup to a genuine catastrophe. It is a plain, fact-driven survey of a field still working out how much warning a mountain can actually give before it erupts.