On a Saturday morning in June 1976, engineers watched a gap rip open across the face of a brand-new $100 million dam in Idaho. Bulldozers sent to plug the leak were swallowed into the dissolving mud, operators were hauled to safety by ropes, and 40 minutes later the entire 310-foot structure disintegrated, unleashing an inland tsunami onto the towns below.

This episode dissects the Teton Dam disaster as a story of human hubris, ignored geological warnings, and bureaucratic momentum. We trace how the Bureau of Reclamation chose a fractured, cave-riddled volcanic site in an earthquake zone, tried to spackle the canyon with grout, rushed the reservoir fill, and blocked its own emergency spillways for a paint job.

• The site sat on highly permeable volcanic rock; the Bureau's own pump-in tests showed the ground drank water instantly ...