©2006, 1997 WGBH Educational Foundation. All rights reserved.

Adapted from NOVA: "Avalanche!". A NOVA Production by the WGBH/Boston Science Unit in association with La Cinquieme and Sveriges Television. Stock footage courtesy of Steve Kroschel, Corbis. Still images courtesy of EM Unit, ARS-USDA, Beltsville, MD. Animation courtesy of Pictures on the Wall.