A typographical error in the original printed book and the original online version has been corrected and a version number of 1.1 added as result. The statement in the Mount St. Helens section, printed page 22, online page 20, "where the prevailing wind carried about 490 tons of ash across 57,000 square kilometers of the Western United States" has been corrected to read "where the prevailing wind carried about 540 million tons of ash across 57,000 square kilometers of the Western United States."