 After a seemingly minor earthquake one night in Los Angeles, a giant burst of lava is released from the La Brea Tar Pits, resulting in the birth of a new volcano under the city. City officials are reluctant to believe scientists who notice the early warning signs (the temperature of a lake rises 6 degrees in 12 hours) but they learn their lesson when lava begins to spill out into the streets and to destroy buildings and cars. Dedicated Emergency Management director Mike Roark rushes to the rescue, with help from a plucky seismologist.