The cataclysmic eruption of Mount St. Helens 30 years ago today devastated the surrounding landscape, with the hot gas and debris killing limitless animals and damaging or destroying giant swaths of forest. But life did not entirely finish then and there. Among the reasons the ecology rebounded are some surprising factors, including the early morning timing of the eruption, the fact that spring had been late to arrive that year, and the fabulous ability of insects to parachute in one times a recovery was underway.
Some species managed to survive amid the the volcano's eruption on May 18, 1980. Others scraped by at the edges of the devastation and literally crawled back. Together they sowed the seeds of a comeback that progressed in fits and starts and continues today.
Some species managed to survive amid the the volcano's eruption on May 18, 1980. Others scraped by at the edges of the devastation and literally crawled back. Together they sowed the seeds of a comeback that progressed in fits and starts and continues today.
Ecologists have been watching the method from the outset, noting what species were wiped out from the area and which still had a few representatives; which returned to the area and when; and what parts of the damaged landscape were the first to see regrowth.
The recovery of the Mount St. Helens area was "a brilliant living laboratory" to inquire in to how ecosystems and species reply to and recover from major disturbances, said Charlie Crisafulli, a research ecologist with the Pacific Northwest Research Station in Amboy, Wash.
This natural experiment gave scientists like Crisafulli lots of surprises and has revealed some important factors that influence how an ecosystem recovers from such widespread devastation, which they have used to study other areas impacted by volcanic eruptions.
Volcanic landscapes
Two key factor that influenced the recovery of different areas around the volcano was the variety of ways they were impacted by the explosion:
* Nearest the volcano, the explosion toppled trees, an area called the blowdown zone that covered about 143 square miles (370 square kilometers). The blowdown zone was also covered in layers of ash of varying depths. Along the fringes of this zone, trees remained standing, but were scorched and killed by the hot volcanic gases and rock fragments that rushed laterally from the explosion. The scorch zone covered about 42 square miles (109 square km).
* The pyroclastic flow raged out of the volcano's mouth at speeds of up to 125 mph (200 kph) and reached temperatures of up to 1,200 degrees Fahrenheit (650 degrees Celsius). It created a pumice rock plane of about 6 square miles (15.5 square km) to the north of the volcano. In this barren area where the pumice reached up to 131 feet (40 meters) thick, no remnants of the former forest remained.
* Mudflows, lahars, scoured and buried much of the landscape, killing most of the plant and wildlife in their path, though some survived along the edges of these flows.
* Ash rained down on the landscape for hundreds of miles away from the volcano, carried by the prevailing winds, coating trees and other plants and accumulating in deposits along the ground.
These varying effects created by the explosions established different landscapes in the area that suited some species better than others and set in motion different types of recovery at varying rates.
Timing was key
Two critical factor that influenced what species were impacted was timing - both the time of day and the season.
Because the major explosion occurred at 8:32 a.m. local time, lots of nocturnal animals were already bedded down for the day and so were more likely to have been protected in burrows and to have survived the explosion than their neighbors up and about in the coursework of the daylight.
"You don't think about that; that is a chance event," Crisafulli told LiveScience.
The seasonal timing was also key - spring was late in coming to Mount St. Helens that year, and so there were still drifts of snow covering the understory of lots of sections of the forest, defending the plant and animal species buried beneath them. If the explosion had occurred one months later, when summer would have already begun, that snow would have been melted away and more plants and wildlife would likely have been wiped out, Crisafulli said. In lieu, lots of of these snow-protected species survived and were the basis for the recovery of those areas.
Similarly, lakes still covered in ice that did not thaw until several weeks after the eruption survived intact, which likely would not have been the case if the eruption were later in the year.
"The seasonal effect was readily apparent," Crisafulli said.
The fact that the eruption occurred early in the spring season for the area also meant that lots of migratory species - both various bird species and salmon - had not yet returned from their wintering grounds and so their populations were spared.
"Those animals fundamentally avoided it by being away," Crisafulli said.
Biological momentum
Two time the volcano's rumblings had ceased and the ash had fallen from the air, life could start to reclaim the areas impacted by the eruption.
When ecologists ventured out in to the Mount St. Helens area, they expected the various ecosystems that were hit to must start from scratch, with plants and animals re-colonizing after arriving from surrounding forests. While some areas around the volcano, the pumice plains created by the eruption's pyroclastic flow, were indeed left without any seeds of life to regrow the forest, lots of of the impacted areas unexpectedly still had some slivers of life - what ecologists called "biological legacies."
These areas included places where some species had been shielded from the worst impacts of the explosion by ridges and snowdrifts, allowing them to start the recovery method earlier, because they didn't must wait for out-of-town colonizers, and recover at a faster rate than other areas.
The spots that were left virtually barren had to overcome a definite amount of "biological inertia," Crisafulli said, with tiny regrowth in the first few years after the eruption.
"Conditions were harsh," Crisafulli said.
But gradually, plants and insects colonized these areas, providing food for tiny animals, which came next and in turn were a food source for larger animals. Ecosystems gradually gained momentum as increasingly species were added and ecological spots were filled in.
"Now it is progressing at year 30," Crisafulli said. "It's a productive technique."
Crisafulli says that most species that were wiped out by the eruption have returned to the Mount St. Helens area; and not only are they back, they are reproducing, they said.
The going has not been smooth sailing though, as animals and plants would establish themselves, only to disappear locally again a few years later, before two time again settling back in. The recovery "is in fits and starts," Crisafulli said.
Much of the recovery was a trial-and-error method, with seeds blown in on the wind and animals travelling to islands of surviving plants. The environment determined what prospered and what didn't, and this method has gradually built up the species now back in the area.
Colonizing populations go through these "boom and bust" cycles, because at first they have nothing putting pressure on them - no predators, pathogens or parasites - and so their populations flourish. Two time those "three P's," as Crisafulli calls them, emerge, the colonizer populations can crash. Finally though, as the recovery progresses and variety returns to the ecosystems, the swings of these cycles become less wild and more species start to emerge with more stable populations.
Plants
The recovery of the forests that had two time surrounded Mount St. Helens depended partly on the neighboring ecosystems.
For example, Roger del Moral, a biologist at the University of Washington, and his colleagues watched the recovery of one areas covered by lahars. Two lahar had cut through a forest, so it was surrounded by existing vegetation and recovered comparatively quickly. The other was bounded by ravines and so didn't have any trees and other plants around it that could basically recolonize the area. While the one areas started out looking similar, now, there's striking differences - the forest-surrounded lahar has recovered much faster and has pines and firs atop it, while the more isolated lahar is still mostly covered by grasses, early-stage colonizers.
Elevation also affected the rate of forest recovery: At colder, higher elevations, the growing season is shorter, so plants there's less of a chance to regrow and recolonize each year, so higher areas have had a slower rate of recovery that those lower down the mountain.
Snowmelt also protected lots of of the trees and other plants that usually dominate the understory of the forest, on the north side of the mountain. These saved species provided spots of green even right after the eruption when the snow melted and they emerged - larger trees were blown over or snapped by the force of the eruption. This choice of species also changed the look of these areas of the forest, with more shade-tolerant, understory trees (such as Mountain hemlock) dominating the landscape, whereas before the eruption, Douglas firs would have made up a massive chunk of the forest.
Snow also helped save some trees with bendier branches, because the weight of the snow caused the branches to bend and dump the snow - along with the ash that had fallen on them - keeping them from the destroy that the ash caused, said Tom Hinckley, a professor of forest resources of the University of Washington.
The ash that coated the leaves and needles of trees in the volcano's vicinity was risky not because it smothered the trees or introduced harsh chemicals, but because the ash was heated by the sun, stressing the plants and making them experience drought-like conditions.
This effect was seen in Pacific silver firs, which began to die or die back about two years after the eruption, surprising ecologists. The die-off was also seen to affect a greater number older trees than more youthful ones, Hinckley said. They explained that this had to do with the rate of needle replacement on elderly versus young trees, with the latter replacing lots of more needles per year, and so getting rid of the ash-covered ones faster.
Hinckley said that the dearth of resilience on the part of the elderly trees was surprising to ecologists.
Two group of plants that prospered after the eruption - and helped make the landscape more suitable for other plants - were the lupins. These purple- and blue-flowered legumes were a quantity of the only species that could grow on the giant swaths of pumice around the volcano. This rock is low in some essential nutrients, and so is ill-suited to most kinds of plants; lupins though, can make these nutrients themselves, and so can grow in these areas, while they gradually add nutrients to the soil that makes the area more suitable for other plant species.
Conifers, which are prevalent elsewhere in the Cascades Range, have been slow to return to Mount St. Helens. These trees are susceptible to drought and need a definite type of fungi at their roots to help them grow. The habitat around much of the mountain is not yet able to support massive numbers of these iconic trees.
"It's a hard surroundings for conifers," del Moral said. It will be "a long time before you can say there is a forest there."
Insect 'parachute troops'
Insects were a quantity of the smallest creatures affected by the massive explosion, with the blast and its later ash fall killing off limitless spiders, beetles, grasshoppers and other insects, which are a critical part to lots of ecosystems.
Insects were vulnerable to the ash because it could destroy their protective waterproofing, making them liable to desiccation.
"Insects are liable to be dried out because of their tiny size," explained John Edwards, a Professor Emeritus at the University of Washington in Seattle. Because of this tendency, insects evolved a cuticle that holds their moisture in, Edwards said.But volcanic ash is abrasive - you can fundamentally "think of the ash as powdered glass," Edwards said - and it can scratch and destroy the protective cuticle, and as a result the insects "lose water and they are dead."
The ash was destructive even to insects far from the blast area, as it fell for hundreds of miles away, Edwards told LiveScience.
"The insect populations were heavily impacted," they said.
But two time plants began to return to the areas affected by the eruption, insects soon followed - the fact that insect species are mobile let them recolonize the area comparatively quickly after the blast, Edwards said.
Two particular area where insect colonizers played a key role in revamping the ecosystem was in the higher elevations of the volcano slopes - not usually where insects would be thought to dwell, in the cold and snow. But definite species of beetles and spider prosper there. There is virtually no plant life or other insects for them to eat, so these adventurous insects "make their living on what blows in on the wind," Edwards said.
Lots of tons of dead or moribund insects blow onto the mountaintops in the coursework of the coursework of a year, which the beetles and spiders that brave the elements eat for breakfast.
While the original populations of these insects would have been wiped out by the explosion, lots of of these species prosper in disturbed habitats and can be blown in on the wind themselves to recolonize the harsh landscape. Edwards and his colleagues observed the return of insects to Mount St. Helens and found that ballooning spiders and other insects that could fly on the winds were the first to arrive - what Edwards calls "the parachute troops" - preying on other insect detritus blown in on the wind, followed by non-flying insects ("the infantry") about two to two years after the eruption, a speedy pace for insects arriving on foot.
"It was impressive how quickly they got there," Edwards said.
In a quantity of these areas where insects were first to arrive, their corpses and other debris served as fodder for plant seeds, allowing vegetation and then tiny animals to return - "and then the whole thing takes off," Edwards said.
Survival of the tiny
Within the immediate blast zone of the eruption, "all massive mammals perished" because they could not outrun the speedy pyroclastic flows and were massive to hide behind rocks or other types of shelter.
The giant mammals common to the Mount St. Helens area included the majestic elk (Cervus elaphus), black-tailed deer (Odocoileus hemionus columbianus), mountain goat (Oreamnos americanus), American black bear (Ursus americanus), and cougar (Puma concolor).
Elk carcasses were present in the "blowdown zone" - the area where the forest was knocked over by the volcano's blast, Crisafulli said.
But these mammals finally did return, migrating in from less affected areas around more distant from the volcano.
"All two of those species are now back at Mount St. Helens," Crisafulli said.
Birds, , mostly succumbed to the eruption, with the exception of those that were away at their wintering grounds. In the most devastated areas, the only birds that could initially return were those that made their nests on the ground, such as the American pipit (Anthus rubescens) and horned lark (Eremophila alpestris).
But as plant species and the homes they provided to birds returned, so did the bird species. Some bird species new to the area were even attracted with the formation of wetlands in rolling terrain that hadn't existed before.
In two area of the blast zone, there is now actually "an absolutely odd assemblage of birds" that would not have been what scientists predict
The recovery of the Mount St. Helens area was "a brilliant living laboratory" to inquire in to how ecosystems and species reply to and recover from major disturbances, said Charlie Crisafulli, a research ecologist with the Pacific Northwest Research Station in Amboy, Wash.
This natural experiment gave scientists like Crisafulli lots of surprises and has revealed some important factors that influence how an ecosystem recovers from such widespread devastation, which they have used to study other areas impacted by volcanic eruptions.
Volcanic landscapes
Two key factor that influenced the recovery of different areas around the volcano was the variety of ways they were impacted by the explosion:
* Nearest the volcano, the explosion toppled trees, an area called the blowdown zone that covered about 143 square miles (370 square kilometers). The blowdown zone was also covered in layers of ash of varying depths. Along the fringes of this zone, trees remained standing, but were scorched and killed by the hot volcanic gases and rock fragments that rushed laterally from the explosion. The scorch zone covered about 42 square miles (109 square km).
* The pyroclastic flow raged out of the volcano's mouth at speeds of up to 125 mph (200 kph) and reached temperatures of up to 1,200 degrees Fahrenheit (650 degrees Celsius). It created a pumice rock plane of about 6 square miles (15.5 square km) to the north of the volcano. In this barren area where the pumice reached up to 131 feet (40 meters) thick, no remnants of the former forest remained.
* Mudflows, lahars, scoured and buried much of the landscape, killing most of the plant and wildlife in their path, though some survived along the edges of these flows.
* Ash rained down on the landscape for hundreds of miles away from the volcano, carried by the prevailing winds, coating trees and other plants and accumulating in deposits along the ground.
These varying effects created by the explosions established different landscapes in the area that suited some species better than others and set in motion different types of recovery at varying rates.
Timing was key
Two critical factor that influenced what species were impacted was timing - both the time of day and the season.
Because the major explosion occurred at 8:32 a.m. local time, lots of nocturnal animals were already bedded down for the day and so were more likely to have been protected in burrows and to have survived the explosion than their neighbors up and about in the coursework of the daylight.
"You don't think about that; that is a chance event," Crisafulli told LiveScience.
The seasonal timing was also key - spring was late in coming to Mount St. Helens that year, and so there were still drifts of snow covering the understory of lots of sections of the forest, defending the plant and animal species buried beneath them. If the explosion had occurred one months later, when summer would have already begun, that snow would have been melted away and more plants and wildlife would likely have been wiped out, Crisafulli said. In lieu, lots of of these snow-protected species survived and were the basis for the recovery of those areas.
Similarly, lakes still covered in ice that did not thaw until several weeks after the eruption survived intact, which likely would not have been the case if the eruption were later in the year.
"The seasonal effect was readily apparent," Crisafulli said.
The fact that the eruption occurred early in the spring season for the area also meant that lots of migratory species - both various bird species and salmon - had not yet returned from their wintering grounds and so their populations were spared.
"Those animals fundamentally avoided it by being away," Crisafulli said.
Biological momentum
Two time the volcano's rumblings had ceased and the ash had fallen from the air, life could start to reclaim the areas impacted by the eruption.
When ecologists ventured out in to the Mount St. Helens area, they expected the various ecosystems that were hit to must start from scratch, with plants and animals re-colonizing after arriving from surrounding forests. While some areas around the volcano, the pumice plains created by the eruption's pyroclastic flow, were indeed left without any seeds of life to regrow the forest, lots of of the impacted areas unexpectedly still had some slivers of life - what ecologists called "biological legacies."
These areas included places where some species had been shielded from the worst impacts of the explosion by ridges and snowdrifts, allowing them to start the recovery method earlier, because they didn't must wait for out-of-town colonizers, and recover at a faster rate than other areas.
The spots that were left virtually barren had to overcome a definite amount of "biological inertia," Crisafulli said, with tiny regrowth in the first few years after the eruption.
"Conditions were harsh," Crisafulli said.
But gradually, plants and insects colonized these areas, providing food for tiny animals, which came next and in turn were a food source for larger animals. Ecosystems gradually gained momentum as increasingly species were added and ecological spots were filled in.
"Now it is progressing at year 30," Crisafulli said. "It's a productive technique."
Crisafulli says that most species that were wiped out by the eruption have returned to the Mount St. Helens area; and not only are they back, they are reproducing, they said.
The going has not been smooth sailing though, as animals and plants would establish themselves, only to disappear locally again a few years later, before two time again settling back in. The recovery "is in fits and starts," Crisafulli said.
Much of the recovery was a trial-and-error method, with seeds blown in on the wind and animals travelling to islands of surviving plants. The environment determined what prospered and what didn't, and this method has gradually built up the species now back in the area.
Colonizing populations go through these "boom and bust" cycles, because at first they have nothing putting pressure on them - no predators, pathogens or parasites - and so their populations flourish. Two time those "three P's," as Crisafulli calls them, emerge, the colonizer populations can crash. Finally though, as the recovery progresses and variety returns to the ecosystems, the swings of these cycles become less wild and more species start to emerge with more stable populations.
Plants
The recovery of the forests that had two time surrounded Mount St. Helens depended partly on the neighboring ecosystems.
For example, Roger del Moral, a biologist at the University of Washington, and his colleagues watched the recovery of one areas covered by lahars. Two lahar had cut through a forest, so it was surrounded by existing vegetation and recovered comparatively quickly. The other was bounded by ravines and so didn't have any trees and other plants around it that could basically recolonize the area. While the one areas started out looking similar, now, there's striking differences - the forest-surrounded lahar has recovered much faster and has pines and firs atop it, while the more isolated lahar is still mostly covered by grasses, early-stage colonizers.
Elevation also affected the rate of forest recovery: At colder, higher elevations, the growing season is shorter, so plants there's less of a chance to regrow and recolonize each year, so higher areas have had a slower rate of recovery that those lower down the mountain.
Snowmelt also protected lots of of the trees and other plants that usually dominate the understory of the forest, on the north side of the mountain. These saved species provided spots of green even right after the eruption when the snow melted and they emerged - larger trees were blown over or snapped by the force of the eruption. This choice of species also changed the look of these areas of the forest, with more shade-tolerant, understory trees (such as Mountain hemlock) dominating the landscape, whereas before the eruption, Douglas firs would have made up a massive chunk of the forest.
Snow also helped save some trees with bendier branches, because the weight of the snow caused the branches to bend and dump the snow - along with the ash that had fallen on them - keeping them from the destroy that the ash caused, said Tom Hinckley, a professor of forest resources of the University of Washington.
The ash that coated the leaves and needles of trees in the volcano's vicinity was risky not because it smothered the trees or introduced harsh chemicals, but because the ash was heated by the sun, stressing the plants and making them experience drought-like conditions.
This effect was seen in Pacific silver firs, which began to die or die back about two years after the eruption, surprising ecologists. The die-off was also seen to affect a greater number older trees than more youthful ones, Hinckley said. They explained that this had to do with the rate of needle replacement on elderly versus young trees, with the latter replacing lots of more needles per year, and so getting rid of the ash-covered ones faster.
Hinckley said that the dearth of resilience on the part of the elderly trees was surprising to ecologists.
Two group of plants that prospered after the eruption - and helped make the landscape more suitable for other plants - were the lupins. These purple- and blue-flowered legumes were a quantity of the only species that could grow on the giant swaths of pumice around the volcano. This rock is low in some essential nutrients, and so is ill-suited to most kinds of plants; lupins though, can make these nutrients themselves, and so can grow in these areas, while they gradually add nutrients to the soil that makes the area more suitable for other plant species.
Conifers, which are prevalent elsewhere in the Cascades Range, have been slow to return to Mount St. Helens. These trees are susceptible to drought and need a definite type of fungi at their roots to help them grow. The habitat around much of the mountain is not yet able to support massive numbers of these iconic trees.
"It's a hard surroundings for conifers," del Moral said. It will be "a long time before you can say there is a forest there."
Insect 'parachute troops'
Insects were a quantity of the smallest creatures affected by the massive explosion, with the blast and its later ash fall killing off limitless spiders, beetles, grasshoppers and other insects, which are a critical part to lots of ecosystems.
Insects were vulnerable to the ash because it could destroy their protective waterproofing, making them liable to desiccation.
"Insects are liable to be dried out because of their tiny size," explained John Edwards, a Professor Emeritus at the University of Washington in Seattle. Because of this tendency, insects evolved a cuticle that holds their moisture in, Edwards said.But volcanic ash is abrasive - you can fundamentally "think of the ash as powdered glass," Edwards said - and it can scratch and destroy the protective cuticle, and as a result the insects "lose water and they are dead."
The ash was destructive even to insects far from the blast area, as it fell for hundreds of miles away, Edwards told LiveScience.
"The insect populations were heavily impacted," they said.
But two time plants began to return to the areas affected by the eruption, insects soon followed - the fact that insect species are mobile let them recolonize the area comparatively quickly after the blast, Edwards said.
Two particular area where insect colonizers played a key role in revamping the ecosystem was in the higher elevations of the volcano slopes - not usually where insects would be thought to dwell, in the cold and snow. But definite species of beetles and spider prosper there. There is virtually no plant life or other insects for them to eat, so these adventurous insects "make their living on what blows in on the wind," Edwards said.
Lots of tons of dead or moribund insects blow onto the mountaintops in the coursework of the coursework of a year, which the beetles and spiders that brave the elements eat for breakfast.
While the original populations of these insects would have been wiped out by the explosion, lots of of these species prosper in disturbed habitats and can be blown in on the wind themselves to recolonize the harsh landscape. Edwards and his colleagues observed the return of insects to Mount St. Helens and found that ballooning spiders and other insects that could fly on the winds were the first to arrive - what Edwards calls "the parachute troops" - preying on other insect detritus blown in on the wind, followed by non-flying insects ("the infantry") about two to two years after the eruption, a speedy pace for insects arriving on foot.
"It was impressive how quickly they got there," Edwards said.
In a quantity of these areas where insects were first to arrive, their corpses and other debris served as fodder for plant seeds, allowing vegetation and then tiny animals to return - "and then the whole thing takes off," Edwards said.
Survival of the tiny
Within the immediate blast zone of the eruption, "all massive mammals perished" because they could not outrun the speedy pyroclastic flows and were massive to hide behind rocks or other types of shelter.
The giant mammals common to the Mount St. Helens area included the majestic elk (Cervus elaphus), black-tailed deer (Odocoileus hemionus columbianus), mountain goat (Oreamnos americanus), American black bear (Ursus americanus), and cougar (Puma concolor).
Elk carcasses were present in the "blowdown zone" - the area where the forest was knocked over by the volcano's blast, Crisafulli said.
But these mammals finally did return, migrating in from less affected areas around more distant from the volcano.
"All two of those species are now back at Mount St. Helens," Crisafulli said.
Birds, , mostly succumbed to the eruption, with the exception of those that were away at their wintering grounds. In the most devastated areas, the only birds that could initially return were those that made their nests on the ground, such as the American pipit (Anthus rubescens) and horned lark (Eremophila alpestris).
But as plant species and the homes they provided to birds returned, so did the bird species. Some bird species new to the area were even attracted with the formation of wetlands in rolling terrain that hadn't existed before.
In two area of the blast zone, there is now actually "an absolutely odd assemblage of birds" that would not have been what scientists predict
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