Virginia Dale was in the first helicopter load of ecologists to land at Mount St. Helens after it erupted 25 years ago this month. "I just remember how bizarre it was going out into that landscape," she says of the suddenly gray, ash-covered terrain. "It gave the impression of total lifelessness."

Dale, at the Oak Ridge National Laboratory in Tennessee, studies ecological succession, or how an environment recovers after a major disturbance. She jokingly calls herself a "disturbed ecologist." When it comes to studying devastation, she says, "Mount St. Helens was off the scale."

The eruption on May 18, 1980, blew away the top 1,314 feet of the mountain, reducing the once symmetrical, glacier-covered summit to a horseshoe-shaped crater. An avalanche of rocks plugged the Toutle River Valley at the base of the mountain and created a 23-square-mile zone of barren, hummocky land. A 300-mile-an-hour lateral blast of hot air and debris flattened the surrounding forest. A cloud of ash climbed to 80,000 feet in 15 minutes and circled the globe in 15 days. Torrents of superheated air, gases and rocks—a mixture known as a pyroclastic flow—surged down the mountain's northern face for hours, destroying everything in its path. All told, the eruption blasted more than 230 square miles of forests, lakes, meadows and streams. It killed 57 people, making it the deadliest eruption in U.S. history, and millions of animals and plants. "Death is everywhere," the Oregonian newspaper reported. "The living are not welcome."

Today, life has returned with a vengeance. Where the avalanche obliterated everything, Dale has counted more than 150 species of wildflowers, shrubs and trees, with an average of ten new plant species gaining a foothold every year. She has also documented five conifer species, including western hemlock and Pacific silver fir, that aren't supposed to be there yet; according to standard ecological theory, those trees should sprout only after generations of other plants have improved the soil and provided some shade. It seems life can take hold even in the most desolate landscape, and in ways no scientist could have foreseen.

Charlie Crisafulli, a U.S. Forest Service ecologist, has been watching life return to the Pumice Plain, a six-square-mile area that was buried in ash and practically sterilized by the pyroclastic flows. Today, the mossy rain-fed ground cover glows chartreuse in the low light. Dense thickets of alders and willows, many 10 to 15 feet tall, grow along new streams that flow across the plain. Frogs croak, birds call. A small herd of elk grazes in the distance. Wildflowers dot the landscape with splashes of red, yellow, pink, white and purple.

It was these purple wildflowers, prairie lupines, that taught Crisafulli one of the key lessons of succession: the importance of chance. Lupines are not typically thought of as plants that colonize the middle of an empty landscape. They spread slowly, hug the ground, and have heavy seeds not easily borne on the wind. But in June 1982, Crisafulli and another ecologist, surveying the Pumice Plain by helicopter, spotted the first plant they'd seen for miles. They landed and found a flowering lupine, surrounded by a ring of seedlings. The deep ash and pumice held few nutrients, but lupines, like other plants in the pea family, get nitrogen from bacteria that live on their roots. Crisafulli established a 200-square-yard study plot around that pioneering plant. Within four years, he counted 16,000 lupines in the plot; three years later, 35,000. "People sometimes ask me how I can go back and study the exact same place year after year," he says. "I always tell them it's never the same."

The flourishing of life on the Pumice Plain may have begun with that lone lupine. Once the plants enriched the soil with nitrogen, adding organic material to it when they died, other plants and then animals soon followed. Within a decade of the eruption, Crisafulli had documented more than 27 plant species in the study plot. A large patch of strawberries sprang up just outside it, probably from a single seed deposited in bird or mammal feces. Crisafulli has trapped 11 species of small mammals on the Pumice Plain, including ground squirrels, mice and shrews. Each has sped up the area's recovery by caching seeds, burrowing through soil and luring predators such as raptors and weasels.

Like many other discoveries on Mount St. Helens, "the return of these small [animal] species flies in the face of conventional wisdom," says Crisafulli. Ecologists once thought that many small mammals stick to tried-and-true routes amid dense vegetation that provides good hiding. But he started finding deer mice in the Pumice Plain in 1982, well before many plants had taken root. Now researchers know that even shrews weighing less than one-fifth of an ounce are hardy explorers that cross miles of barren terrain.

The great eruption had some other surprising effects on the balance of life in the rest of the region. "Be careful where you step as we approach the lake," says Crisafulli. At first I don't understand the warning; the terrain is level and we are walking on a four-foot-wide path. But then the ground seems to move. I look closer. Tiny, dark western toadlets hop everywhere. At this lake, thousands of them pulsate in piles along the water's edge.

As luck (for the toads) would have it, the amphibians are abundant here because they happened to be hibernating underground when the volcano exploded in 1980. By the time the animals emerged a month or so later, the eruption had blasted down all the trees around the lake. More sunlight hit the water, making it unusually warm and especially rich in the aquatic organisms toads feed on. The blast also killed off most of the toads' predators. Intriguingly, the western toad is declining in most of its range beyond Mount St. Helens. "It may be a species that prospers with disturbance," says Crisafulli, "which no one had suspected."

Toads here, shrews there—the scattering of volcano survivors and opportunists suggests that the return of life occurs simultaneously in thousands of places at once, says Jerry Franklin an ecologist at the University of Washington in Seattle. The lesson applies to other damaged ecosystems, he says. Loggers shouldn't clear-cut the land, for instance, but instead leave behind "lifeboats" such as snags and living trees that will sustain other organisms and foster recovery.

Mount St. Helens' recovery has had many setbacks since the 1980 eruption. Stream erosion washed away some of the research plots. Landslides buried emerging forests. And other eruptions unleashed devastating pyroclastic flows. This past fall, Mount St. Helens erupted for the first time since 1986, sending up a cloud of steam and ash. The rumblings have continued unabated, but Crisafulli and Dale don't mind. They welcome disturbances.