Book excerpt: In 1993 Stanley Williams, an eminent volcanologist, was standing on top of a Colombian volcano called Galeras when it erupted, incinerating several of his colleagues instantly. As Williams tried to escape the mountain's fury, the volcano pelted him with white-hot projectiles travelling literally faster than speeding bullets. Within minutes he was cut down, his skull fractured, his right leg almost severed, his backpack aflame. Williams lay helpless and near death on Galeras' flank as volcanic bombs continued to rain down on him until two brave women - friends and fellow volcanologists - mounted an astonishing rescue effort to carry him safely off the mountain.The tale of how Williams survived Galeras becomes the framework for this fascinating book about the tiny group of scientists who risk their own lives to save others. It is also an absorbing account of volcanoes, and their physical and cultural impact: Vesuvius' famous explosion in AD 79; the Laki eruptions in Iceland in 1793; and the subsequent 'haze famine' which killed one fifth of the population; and Tamboura, which, in 1815, plunged an area of 300 miles into darkness for two days.