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35 years after Mount St. Helens eruption, nature returns

Before Mount St. Helen's blew its top 35 years ago today, Spirit Lake was a popular tourist destination in Washington state, a place dotted with campsites where visitors came to enjoy its crystal clear waters that reached depths of 200 feet.

Within hours of the 1980 eruption, the lake disappeared under layers of volcanic ash, tree limbs and mud. The blast - the deadliest and most economically destructive volcanic eruption in U.S. history - caused an avalanche that came crashing down onto the lake, displacing the water to such a degree that it produced huge waves that washed across the mountain landscape. The landslide raised the lakebed 200 feet.

After May 18, 1980, five more explosive eruptions of Mount St. Helens occurred in 1980, including this spectacular event of July 22, which sent pumice and ash 6 to 11 miles into the air. Mike Doukas, USGS

"That landslide completely buried the old lake," University of Washington Tacoma's Jim Gawel, who has spent the past decade studying the lake, told CBS News. "You basically buried all the old sediments, knocked down all the old trees and denuded the landscape. So you kind of started from scratch."

It seemed as if one of the region's great natural landmarks - a lake by some accounts 4,000 years old - was gone forever. But nature had other ideas. Because runoff still drained into the same spot, a new lake began forming.

Today, visitors see a complete new lake - albeit covering a much wider area and shallower, which has been a boon to aquatic life.

"It was a shock to people how quickly the lake recovered," he said. "Everybody was thinking, God, this will take forever for the lake to come back and for the landscape to come back. Everybody was surprised they were starting to see signs of life within a year."

Much like the lake, the hundreds of square miles of century-old forests destroyed by the eruption have come back, in many ways richer and surprisingly different than before. Such a recovery would have seemed unfathomable for anyone who witnessed the destruction on May 18, 1980 that was triggered by a 5.2-magnitude earthquake at 8:32 a.m.

A 2012 image of Spirit Lake, which had been buried by the Mount St. Helens eruption and since reborn. Liz Westby

Soon after, the volcano's northern bulge slid away, causing the biggest debris avalanche in recorded history. The landslide was soon followed by a lateral blast that sent hot ash and debris hurdling down the mountain at 300 miles an hour, scorching and toppling everything with 230 square miles. It also sent ash and gas 15 miles into the air in just 15 minutes. Over the next nine hours, prevailing winds sent 520 million tons of ash across the state - darkening an area as far away as Spokane, Washington, more than 250 miles to the northeast.

Fifty-seven people lost their lives in the eruption. The area's abundant wildlife was also devastated. Some 7,000 big game animals and 12 million juvenile salmon were lost. No trees from a dense forest were left standing within 6 miles of the summit.

There is no question the avalanches and eruption transformed the landscape - forming new lakes and ponds, filling in valleys, covering much of the forest floor with ash. But out of the devastation has emerged a new ecosystem, challenging what we know about the ability of landscapes to recover after a disaster and is serving a model for other parts of the world like Chile and Indonesia where volcanoes have charred whole ecosystems.

Charlie Crisafulli, an ecologist with the U.S. Forest Service Pacific Northwest Research Station, was among the first scientists to arrive in the weeks after the disaster. Flying towards the blast site, he recalled seeing green forest give way to miles and miles of "gray, strewn with downed trees."

"The initial impression was that nothing or few things would survive," Crisafulli recalled. "It looked like everything had been destroyed, that all vestiges of life had been snuffed out."

The images are from the same forest site in 1980 after the Mount St. Helens eruption, at left, and in 2013, right. Joe Antos and Dylan Fischer

But on the ground, he saw the first signs of life. Ants scurried about and pocket gophers dug through the ash, burrowing in search of food. Fallen trees provided homes for insects and infused much-needed nutrients into the parched system. Further up the mountain, many alpine lakes and their aquatic systems came away unscathed because they had been protected from the ash by ice and snow.

Oregon State's Don Zobel, who also arrived weeks after the eruption to study plant life, found a forest floor covered in several inches of tephra, fragments of volcanic ash and rock that was gray in color and looked like a concrete floor.

Many small plants, moss and shrubs had been buried alive, but like Crisafulli, Zobel saw signs of life in the first year. Species of moss found in the wake of wildfires thrived. So did Rubus lasiococcus or dwarf bramble, which was able to use vine-like runners to spread across the tephra.

"Those runners moved out through the cracks and spread over the tephra in a hurry," he said, adding that iarella unifoliata or foamflower and Erythronium montanum or avalanche lily also did well.

These plants and animals were what scientists call biological legacies, species that determine the pace and direction of the new ecosystem. And because there were some survivors already there, they helped jumpstart the desolate landscape.

"In this enormous sea of destruction, we had this archipelago of survivorship. These islands - from a single individual plant to entire lake - turned out to be incredibly important," Crisafulli said. "One of the biggest challenges for plants and animals to reestablish has to do with dispersal. So if you have survivors deeply embedded in a disturbed area, that kind of negates the limits of long distance dispersal."

Ecologist Charlie Crisafulli measures the current annual growth of red alder tree branches that have colonized riparian habitat in the South Coldwater Creek debris avalanche deposit, Mount St. Helens. US Forest Service

Soon after the blast, Congress created the 110,000-acre Mount St. Helens National Volcanic Monument. That gave scientists a rare chance to sit back and watch nature proceed at its own course undisturbed by manmade activities like logging, which altered much of the area surrounding the site.

They were in for plenty of surprises - especially in places where the landscape was dramatically transformed. These were areas buried by the landslides, or where the old growth forests, which had defined the ecosystem for hundreds of years, were now gone.

"In some places, it doesn't even make sense to talk about recovery," Crisafulli said. "We are talking about new landforms and there is no possibility of returning to precovery."

Vast areas once dominated by towering trees were now open to sunlight, giving a whole host of plants, insects, birds and small mammals a chance set up shop. And with huge stretches covered in volcanic ash lacking in minerals needed for plant growth, those that could draw the nitrogen from the air and then store it in their roots - called nitrogen fixation - had a distinct advantage.

Thus, some of the early colonizers in these desolate patches were plants like prairie lupine, famous for their purple flowers, fireweed and pearly everlasting and alder shrubs. At the same time, the conifer forest haven't come back, replaced by deciduous forest dominated by alder trees, which fix their own nitrogen. Sitka willow took hold in areas of high moisture, like stream embankments.

A white-crowned sparrow was one of the bird species that took advantage of the open spaces created by the Moung St. Helens eruption to thrive. Charlie Crisafulli

These emerging forest attracted ants and grasshoppers and generalist birds like American robins - attracted to the open spaces. Other newcomers were horned larks and savannah sparrows alongside gophers and deer mice.

More recently, a new chapter in this story has emerged as many of the trees in these new forests reach the point where they are creating a canopy, Crisafulli said. That has brought changes in light, soil moisture and wind - and with it a host of new species.

Out goes the fireweed and in come the sword fern, lady fern and Lily of the valley. The ants fall back, replaced by leaf-eating insects and rove beetles. The gophers find the new world less suitable, replaced by chipmunks, ground squirrels, voles and shrews. Weasels also make their appearance.

Elk, too, arrived to take advantage in explosion of new plant growth, increasing to record numbers. This thickening forest also impacts birds, with sparrows replaced by American yellow warblers and willow flycatchers, among others.

Spirit Lake, too, has benefited from the loss of the huge trees that once cast a shadow over it. Combined with its shallower depth, Gawel said this has resulted in a "warmer, more productive lake" when compared to alpine lakes in the region.

This image was taken June 8, 1980, of avalanche lilies growing through blast deposits from the May 18, 1980 eruption of Mount St. Helens, about 10 miles northwest of the volcano. USGS

That has resulted in more aquatic plant growth, he said, more insects and bigger fish - in this case rainbow trout that were introduced soon after the eruption. Salamanders, which are abundant in most alpine lakes in the region, are scarcer here because of the fish.

"It's hard to say the lake is better than before. I would say it's more productive. There are a lot more fish, a lot more stuff going on in this lake," Gawel said.

The lake has also benefited from downed trees from the blast that to this day float from one end to the other depending on the wind - covering a fifth of the lake and serving as a hotbed for insects.

"What we are finding is that logs are creating nutrients by themselves. There is a biofilm that grows on the logs and the logs are constantly feeding the biofilm into the lake. You get this floating ecosystem."

Not all places, however, have thrived. In the four sites Zobel studies further from the crater, where tree loss was less, the plant growth has dropped off. There are only about quarter to a half of the mosses that were there before the blast. In places covered with six inches of tephra, herbaceous plants are only 30 to 60 percent of what they once were.

"We had a nice recovery of the plants going for the first 20 years and the curve flattened. There hasn't been any recovery from 2000 to 2010," he said. "We really don't know what is causing that."

But overall, Crisafulli and others would argue the areas hit by the blast are doing just fine - more diverse and species-rich than the old growth forest that dominated for so long and healthy by most standards. Invasive species, a fear early on, have not proven to be a problem.

Crisafulli, who looks the part of an outdoorsman with his weathered face and salt-and-pepper goatee, plans to spend a good chunk of the year around Mount St. Helens, as he has for the past 34 years studying the ongoing changes to the ecosystem. Even after all this time on the mountain, he still sounds in awe of place that is proving to be a textbook example of nature's resilience.

"Restoration efforts weren't really need because life is enormously competent and well practiced at reinsinuating itself into disturbed areas," he said. "Our expectation should be that life is incredibly tenacious."

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