The little “Entering the blast zone” sign on the edge of the highway tells the Mount St. Helens revival story.

Twenty-five years after the volcano’s catastrophic 1980 eruption, the boundary of the 230-square-mile blast zone is so lush with life that newcomers probably wouldn’t notice it without a hint.

The renewal isn’t limited to the land surrounding the Highway 504 reminder, where evergreens planted post-1980 have developed into vigorous Weyerhaeuser Co. timber stands. Life endures even in the heart of the ruin, in places sterilized by the volcano and where people haven’t interfered with Mother Nature.

The May 18, 1980, eruption destroyed a picture-perfect mountain landscape that campers and climbers loved. A blast with the force of a nuclear explosion tore up the old-growth forest that once graced the mountain’s slopes.

But it did not snuff out all living things around Mount St. Helens, where an amazingly diverse array of flora and fauna now thrives. It’s a different environment than before 1980, but perhaps more intriguing, particularly for scientists who still study the effects of the disturbance.

Not only has life around the mountain proved more resilient than scientists imagined, but the renai ssance also appears to be picking up steam.

“The greening of the landscape has been very pronounced in the last five years or so,” said Peter Frenzen, a Mount St. Helens National Volcanic Monument scientist who came to study the volcano after the 1980 eruption and never left. “Within the next 25 years, parts of the debris avalanche will be completely forested with red alder.”

The renewal began immediately after the eruption. Researchers quickly noticed that snow on north-facing slopes had protected young trees, roots and seeds from the full force of the explosion. Those that persisted jump-started the revival.

While big animals – elk, deer, cougar, coyotes – instantly died in the eruption, little ones, such as gophers and mice, survived. And within a few years, a wide variety of animals found homes in the area.

The only natives that haven’t come back to the blast area are ones that no longer can find a home there. Though young trees have taken root all over, it could take 40 or 50 years for the forests to shape up enough to appeal to the northern flying squirrel and the red-backed vole, which prefer old growth.

Though that habitat is gone, the eruption created a new kind of environment hospitable to animals that don’t live in forests.

Birds, in particular, are drawn to the open areas of the debris avalanche. They include western meadowlarks and horned larks, birds more typically seen in the shrub-steppe areas of Eastern Washington, said Charlie Crisafulli, a U.S. Forest Service research ecologist who has studied habitat changes around St. Helens for nearly 25 years.

“People often think of disturbance as reducing habitat,” he said. “It’s also a generator of habitat.”

Last fall, when St. Helens shook itself awake after 18 years of quiet, the renewed eruption refocused attention on the powerful volcano and its recent history.

The latest series of steam-and-ash eruptions, beginning in October, has affected little outside the volcano’s horseshoe-shaped crater. A new mound of lava continues to grow inside it.

Scientists admit they can’t be sure what will take place next, but don’t expect anything as dramatic as what happened on May 18, 1980.

SPIRIT LAKE REINVENTS ITSELF

After the eruption, teams of scientists turned the blast zone into a laboratory to study how nature responds to disturbance.

Perhaps the most spectacular turnaround has taken place at Spirit Lake.

Before the 1980 eruption, Spirit Lake was a picturesque vacation getaway. The clear, steep-sided lake, surrounded by forests, also was home to Harry Truman. The crusty old resort owner became famous when he defied danger warnings and refused to leave his home. Truman was among the 57 who died in the eruption.

When St. Helens collapsed, it clobbered Spirit Lake with debris. The impact of the landslide forced a wave of water to slosh against the slopes of surrounding valleys, where it knocked down trees and yanked them back into the lake. Hot volcanic rocks and minerals also degraded the water.

Spirit Lake never will look the same. The eruption lifted it up more than 200 feet, dramatically expanded its area and left it much shallower than it was before the eruption. A raft of dead logs still floats on the surface.

Douglas Larson, an Army Corps of Engineers limnologist, or lake specialist, who first visited Spirit Lake in August 1980, was overwhelmed.

“The water was black,” said Larson, who is now retired and lives in Portland. He described post-eruption Spirit Lake as “a roiling, steaming body of degraded water choked with logs and mud,” in a 1993 article in American Scientist magazine.

The water was “a microbial soup,” toxic to fish and host to all kinds of bacteria, Crisafulli said. Pathogens included “red zone fever,” a mild form of Legionnaire’s disease, which infected Larson and several others who studied the lake after the eruption.

Larson and other scientists who tested the water after the eruption predicted it would take 10 to 20 years for Spirit Lake to return to pre-eruption conditions. But the scientists were wrong. It took only a few years for the lake to clear itself to the point that its quality mirrored that of other alpine lakes.

“We were very surprised how fast it recovered,” Larson said.

Scientists discovered plankton, or microscopic fish food, in the water a few years after the eruption. Now thousands of rainbow trout populate Spirit Lake, Crisafulli said.

Before 1980, state fisheries officials annually planted 40,000 rainbows in Spirit Lake. But that stopped after the eruption. Recreational fishing hasn’t been legal at Spirit Lake since then. The lake is part of the 106,255-acre volcanic monument, which is devoted to natural recovery.

Officials suspect someone secretly planted rainbows in Spirit Lake sometime before 1993, when researchers caught the first one.

“The table was set for the fish when they first appeared,” said Pete Bisson, a U.S. Forest Service fish biologist. “The key appears to be the rich weed beds that developed where the landslide went into the lake.”

Crisafulli said six species of pond weeds now grow in water 8 feet deep along the south shore.

“It’s like a forest,” he said.

The fish consume the bugs, snails and salamanders found there.

Some of the rainbows Crisafulli has captured are 25 inches long and weigh 5 pounds.

“They’re growing exceptionally fast,” Bisson said.

Fish this size are unusual for high mountain lakes, because the lakes usually don’t produce much plankton, the organisms at the bottom of the food chain.

That’s true of Spirit Lake as well. The latest water-quality data suggest the lake has a split personality. Along the south shore, fish find lots to eat. But several hundred yards out, plankton growth is limited.

“It’s almost like you’ve got two different lakes,” Larson said.

As for the fish, no one knows whether they’ll continue to prosper. If they deplete their food supply, they might not grow as fast. But they have no major predators. While eagles, ospreys and otters can take them, people can’t.

“They have a pretty good situation,” Bisson said.

ELK POPULATION BOOMS

Visitors driving along Highway 504 to Mount St. Helens probably won’t see fish. But it’s a good bet that rangy, white-butted elk will wander into view.

And even if visitors don’t see the elk, hikers are bound to encounter the animals’ pellet-sized scat on the trails. Or notice how its appetite for new shoots has stunted the growth of many of the monument’s small firs.

Elk died in the 1980 eruption, but it didn’t take long for others from outside the blast zone to repopulate the area. Munching on grasses, leafy plants and young tree sprouts, they multiplied rapidly. The herd grew at near record rates between 1983 and 1986.

“It was almost an ideal situation for elk,” said Fred Dobler, a regional wildlife manager for the state Department of Fish and Wildlife.

They gravitated to the open areas created by the eruption. And within the monument, hunters couldn’t shoot them.

About 2,000 elk now wander in and out of protected lands.

“That’s about what it was before the eruption,” said Frenzen, the Mount St. Helens National Volcanic Monument scientist.

The elk are so plentiful that state wildlife officials began a relocation program in 2003. They captured and hauled 41 elk from the St. Helens herd and set them free in Skagit County, where elk aren’t as numerous. A similar catch-and-release project, targeting 50 elk, is planned for later this year, Dobler said.

NEW WETLANDS LURE UNUSUAL SPECIES

“The volcano created a tremendous amount of wetland habitat,” Frenzen said. “The amphibians have taken advantage of that, as have the bird communities. Getting there is not the problem for most organisms. … If you build it, they will come.”

On this day, Frenzen was in tour-guide mode, leading a small group of visiting journalists along a roller-coaster trail through what scientists call the hummocks, giant lumps of rock and debris that slid off the volcano in 1980. A virtual sieve of ponds – some seasonal, some year-round – fills the surrounding dips.

Before the eruption, there were 39 lakes and ponds in the blast zone. Now there are 150. Water pools in places it didn’t settle before the eruption altered the landscape.

“The Mount St. Helens area weeps with seeps,” said Crisafulli, another host of the group.

Scientists believe the region’s moist, maritime climate hastened recovery around the mountain.

In 1981, when scientific surveys began, “we didn’t find a single plant,” Frenzen said. Now, the hummocks area is crowded with water-loving willows and alder. The alder grow about 3 feet per year.

At one spot, Frenzen pointed out a downed log, clearly marked by the teeth of the beaver that felled it. River otters also have been a fixture in the wetlands for almost 20 years.

Bufflehead ducks floated around a nearby pond until visitors scared them into flight. A western meadowlark called.

“Right now this is a place of great bird diversity,” Crisafulli said.

It’s not just the larks. Red-winged blackbirds have taken up residence, as have water pipits. Migrant species, such as warblers and fly catchers, also come through.

A chorus of male Pacific tree frogs noisily introduced itself. It might not be a surprise that the most common frog species in Washington was among the first two amphibians to colonize the newly created ponds.

The other pioneer was the western toad. Unlike the tree frog, the western toad populations have declined in Washington, particularly along the Interstate 5 corridor.

“Mount St. Helens definitely stands out as the exception,” said Kelly McAllister, a wildlife biologist for the state Department of Fish and Wildlife.

Oddly enough, a mottled brown toad crossed the trail in time for Crisafulli to pick her up and identify her as a western toad. He gently poked her to see if she was pregnant – she wasn’t – then set her down again.

“There you go, sweetheart,” Crusafulli said. “They’re not elegant hoppers. They just kind of crawl. She’s coming out after six months underground.”

On another spring morning, Crisafulli pulled on a dry suit and a diving mask and paddled through a pond where at least 60 breeding pairs reproduce. Crisafulli knows where to look because amphibians have been a focus of his studies for several years.

On the pond’s far edge, he found the mother lode of eggs in the submerged branches of a willow. Hundreds of thousands of tiny western toad eggs, strung out like beads in jelly necklaces, were wrapped around the shrub.

“This whole area is black with them,” Crisafulli said.

A few jilted males floated in the water nearby.

“What we’re seeing are a few males that weren’t lucky enough to get in on the action,” Crisafulli said.

The toads are just one example of a species well suited to the new habitat, Crisafulli said.

“What determines what is here is structure,” Crisafulli said.

He compared the change in habitats around Mount St. Helens to a cityscape.

“The architecture went from being simple to very complex,” he said.

That has given a wide variety of species a natural foothold in the blast zone.

To Crisafulli, the rebirth ought to teach people to resist the urge to tamper with nature.

“We always want to run in and fix things,” he said. “Maybe we should let them be.”