Volcano Pearl, 9.30pm An unprepared Los Angeles is facing its worst nightmare, as a stream of fiery deadly lava creeps insidiously across traffic-choked streets while wreaking havoc in the natural and man-made tunnels of the city. Tommy Lee Jones stars as the city's emergency chief facing the ultimate challenge. Secrets Of The Viking Warriors National Geographic, 8pm In the ninth century, the Vikings dominated Europe. Two hundred years after they started pillaging, they had invaded England, attacked the world's wealthiest empire, Byzantium, and were poised to colonise North America. How did they achieve all this? And why did they disappear from history?