Secrets Underground

Rob Nelson journeys to California to study an interconnected system of major fault lines that might set off a mega‑quake, assessing the hidden risks beneath the state’s surface. He also delves into a mysterious sinkhole, probing its origins and potential impact.

California's Hidden Doomsday is a television episode that fits within the documentary genre, presenting a factual look at geological threats. The programme follows a single presenter as it moves through on‑screen investigations, offering viewers a clear picture of the hazards that could affect the West Coast. Rob Nelson travels to California with the aim of examining a linked system of major fault lines. He looks at how these fractures in the earth’s crust might interact and potentially trigger a massive, or “mega‑”, earthquake. By tracing the connections between the faults, he highlights the scale of risk that such a seismic event could pose. In addition to the fault‑line study, Nelson turns his attention to a puzzling sinkhole that has appeared in the region. He investigates the formation of this cavity, documenting its size and the surrounding terrain while trying to understand what might have caused it to develop so suddenly. The episode weaves together these two investigations, showing how both deep‑seated tectonic structures and surface‑level collapses can threaten communities. By following Nelson’s on‑site work, viewers get a concise look at the hidden dangers lurking beneath California’s landscape, without venturing beyond the facts presented.