Thirty years ago, on May 18, Mount St. Helens lost its top—3.7 billion cubic yards of mountain, to be exact. The peak of the Pacific Northwest icon dropped by about 1,300 feet in a matter of seconds, taking down with it enough trees to build 300,000 two-bedroom houses. Gone, too, were 200 homes, 57 human lives and most of the visible wildlife across 230 square miles.

"The first reaction for many of us was that what remained was a moonscape," recalls Jerry Franklin, professor of ecosystem analysis at the University of Washington. "But that proved to be very wrong."

Those initial bleak impressions were based on aerial views. As scientists got a closer look at the ash-laden ground, they discovered that the devastating losses had made room for remarkable gains—in terms of both ecosystem productivity and scientific progress.

Plants and animals that never stood a chance under heavy canopies of trees, or in the presence of predominating predators, began to flourish. Some of these species were brand new to the area, such as the western meadowlark. The resulting early-successional ecosystems turned out to be even more productive than those of the pre-eruption old-growth forests.

As the years went by, several lessons in fields ranging from biology to engineering to atmospheric science piled up. Zoologists studied curious cases of spiders windblown into the blast zone; volcanologists engineered stainless steel "smart spiders" to monitor ongoing volcanic activity; and forest managers took notice that areas left untouched by human hands after the eruption fostered greater biodiversity than places where people attempted to speed recovery by salvaging dead trees and planting new ones.

"For a lot of the scientists, including myself, it was kind of like being a kid in a candy store," Franklin says. "There was so much going on, and so many surprises."

View a slide show of 11 scientific lessons learned from study of the blast at Mount St. Helens