Scientists were stunned to find survivors on volcano-ravaged Mount St Helens, Steve Farrar reports.
May 18 1980, 8.32am. A bright, chilly morning on Mount St Helens in Washington state. Dave Johnston glanced towards the peak some five miles to the south as the earth shook ominously beneath his feet. For some weeks, the great volcano had been rumbling and spluttering like a waking giant. The geologist had been expecting something to happen but the drama about to unfold before his eyes was far beyond anything he could have envisaged.
It started a mile below the crater. A 5.1 magnitude earthquake rattled the mountain, whose bulging northwest flank simply could not take the strain. The entire side of Mount St Helens slid away, unleashing a vicious gout of pulverised glassy rock, heated to some 350C, which blasted into the valley below at more than 300 miles per hour. Understandably, Johnston thought his monitoring position was a safe distance from any eruption but as he watched this tide of destruction rush towards him he knew he was in trouble. The radio link he had with colleagues crackled a final "Vancouver, this is it" before falling silent.
Johnston was one of the 57 people who died on the mountainside that morning. The blast cut a 230-square-mile swathe of utter devastation through the countryside. Combined with the immense landslide, ash falls and searingly hot pyroclastic flows that the crater emitted, Mount St Helens had abruptly wiped plant and animal life from its northwestern flank. When the scientists returned to the scene in helicopters, they gazed out over an apparently sterile, almost lunar landscape.
Such volcanic devastation has been witnessed on many occasions. This time, however, there were teams of experts with resources that only the world's richest nation could spare to record the impact of this most spectacular natural disaster. Many of these scientists, based at the nearby University of Washington at Seattle and neighbouring institutes, were perfectly placed to study the legacy of that May morning. For two decades they have watched life recover lost ground, seen the ingenuity of nature at work on greening the land afresh. One described it as "a beautiful natural experiment". Attention focused on the blast zone. Other flanks of the volcano had suffered damage during the eruption but life soon re-emerged through the thick cloak of ash to return things almost back to normal within a few years.
But in that plume of destruction, the ground blasted, seared and crushed, they surmised that virtually nothing could have made it through. Roger del Moral, professor of botany at the University of Washington, was among the first to return. He recalls the alien terrain that greeted him: "There was just nothing there. Our feet sank into the ground, which was still hot six weeks later - it was utterly barren." Yet it soon became apparent that this desolate landscape was far from sterile, and the survivors quickly made their presence felt.
Where the blast and pyroclastic flows hit with full force, nothing made it. But throughout the zone there were pockets of life. Undergrowth such as red elderberry and gooseberry, where it had been cocooned in snow and protected by steep, north-facing slopes clung on. These would surely provide the nuclei from which the recolonisation would begin, the experts reasoned. Wrong again, del Moral observes. The survivors did indeed thrive but never moved to the newly virgin land. That task was one for the specialist pioneers, whose seeds soon arrived, blown on the wind to take advantage of this remarkable opportunity.
Early arrivals included tough herbaceous plants that could thrive on the most meagre levels of nutrients, such as fireweed and pearly everlasting. They used the pockets of survivors as bridgeheads and then moved outwards with tremendous zeal. Along with those first seeds, possibly even before, came a gossamer compost, made up of the carcasses of insects, spiders and pulped organic debris. These slim pickings would have been blown by the wind throughout the area, providing a miserly source of nutrition even above the vegetation line. Miserly, perhaps, but sufficient for a few insects that combined hardiness with a remarkable penchant for travel, such as the tiny carabid beetle. John Edwards, professor of ecology at the University of Washington, says: "The first true pioneers were these predatory and scavenging beetles that could live on the material blown into this bare, moon landscape."
By the end of that first summer, within a few months of the eruption, these beetles were to be found all over Mount St Helens. Spiders parachuted into the area on wind-borne threads of silk to scratch out a living. Edwards argued that these first animals and the detritus they lived on may even have provided the nutrients to help the first plants establish themselves.
By 1984, the pioneer plants were surging out from the refuges to re-establish themselves on the landscape. The key to their early success was the ease with which their seeds could travel great distances on the wind to reach these remote sites. "They were commando soldiers parachuting into a site surrounded by the enemy but once they found a foothold, they were in," says del Moral.
As the vegetation returned, the insect pioneers moved out, unable to compete with other species that were now able to get by. Other, less mobile plants, did eventually reach the area, many deposited from the stomach contents of elk that were already wandering across the devastated landscape within a month of the eruption.
Amazingly, a few larger animals survived. Pocket gophers, shielded from the mayhem in their burrows, dug themselves free and managed to survive in some especially barren areas. Frogs and salamanders that hid in the sediment at the bottoms of ponds also survived. Jerry Franklin, professor of eco-system analysis at the the University of Washington, said that after one early helicopter trip into the devastated zone, the scientists were amused to find the pilot attempting to fish in what they assumed was a dead pool. "We thought that was pretty dumb until we saw he had actually already caught some fish," he said.
It is still a damaged landscape that greets the visitor. "You are still more impressed by the bareness than by the presence of life," says del Moral. But the lesson the scientists have taken from the the two decades of regrowth on Mount St Helens is just how resilient nature is.