Volcanic eruptions are among the most fascinating natural phenomena and can have significant impacts upon the environment. One only has to think of the 1883 eruption of Krakatau or of the 1980 eruption of Mount St. Helens to get a sense of the awesome power and wide-ranging impacts of eruptions. Some readers will remember hearing or reading about the loss of life and devastation around those volcanoes, while others will remember how even larger eruptions than these cooled the Earth's climate and affected the ozone layer. Most will recall controversial discussions about how volcanoes may have eradicated the dinosaurs some 65 million years ago or about how super-eruptions may have nearly wiped out our human ancestors some 75,000 years ago. We like to think it is fortunate that they did not, but what will happen when the next super-eruption strikes? Most recently, eruptions at ocean island volcanoes have even been proposed as triggers for catastrophic, massive volcano failure and the generation of tsunami waves of unimaginable proportion. The 26 December 2004 Banda Aceh tsunami; off Sumatra, which devastated coastal areas in SE Asia, killing 300000 and precipitating several million people into a state of absolute poverty, is a small event in comparison. Volcano-related mega-tsunamis represent a very great risk to many coastal cities around the world and to their populations, and no doubt to the world economy. Moreover, it has now been demonstrated that periods of severe cooling lasting 1000 years are unambiguously correlated with eruptions.