57 Victims Were Outside the Danger Zone. Here's Why.

Fifty-seven people died when Mount St. Helens erupted on May 18, 1980. The story told for years was that they'd ignored the closed zone. By the count in Steve Olson's book "Eruption," only three of them were inside it, and two of those had permission to be there. This video lays two maps on top of each other: the danger zones Washington drew in April 1980, and the ground the lateral blast actually covered. The zones were built around the mountain's own record, where past sideways blasts stayed narrow and close. On May 18 the bulging north flank slid away first, which suddenly unloaded a hidden body of magma and its pressurized hydrothermal system. The blast went out sideways through the gap, at 300+ mph, as far as 17 miles, and over the ridges in between. It also covers how the west side of the zone was drawn, what the 1978 USGS hazard report got right, and how hazard maps changed after 1980.