On August 21, 1986, violent explosions rocked Cameroon’s Lake Nyos. A wave of water over 15 meters (around 50 ft) high flattened vegetation along the southern shore, but a second deadly, nearly invisible wave of carbon dioxide blanketed the nearby towns, suffocating residents and animals. In this episode of #Untold, a new #YouTubeLearning series from ACS, PBS, and YouTube, we investigate how a lake could explode and shoot out a gigantic wave of deadly carbon dioxide gas.