Pyroclastic Flows
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- Prior to 1980, the valley north of Mount St. Helens was cloaked in majestic old-growth forests.
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- No trace of the pre-eruption forest remained after the eruption. [Summer, 1980]
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- Close-up view of the forest north of the volcano. [Before 1980 eruption]
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- Same view, the original surface lies beneath more than 150 feet (45 m) of landslide and pyroclastic flow deposits. [1 year after eruption]
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- Fiery flows of pumice and gas were erupted periodically for more than a year following the eruption.
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- A geologist examines explosion craters formed as ground water flashed to steam in the fiery deposits.
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- The first life observed was limited to wind-dispersed insects and spiders. [1 year after eruption].
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- Ballooning spiders and carabid beetles survived by feeding on the carcasses of a variety of insects blown in by the wind.
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- The first plant to colonize was the praire lupine, a hardy nitrogen-fixing subalpine plant. [2 years after eruption]
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- Dead lupines left behind fertile leaf litter that trapped the windblown seeds of less hardy plant species.
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- As the lupine spread, it enriched the pumice, paving the way for other plants to follow.
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- Runoff from rain and snowmelt carved deep gullies in the the valley north of the crater.
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- The gullies emptied onto large floodplains where repeated erosion and burial has limited plant establishment.
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- Groundwater springs were important sites for early plant establishment, forming oases on the otherwise barren pumice.
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- The availability of food and hiding cover around the springs supports 11 species of small mammals.
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- Small fir, hemlock and pine trees mark the beginning of a future forest.
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- The once barren pumice is teeming with life.
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- Barren pumice covers the once forested valley. [1 year after eruption]
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- Crater floods and mudflows eroded and buried the pumice [5 years after eruption]
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- Fine sediments deposited by wind and water cover the boulders [15 years after eruption]
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- After three decades, life has returned to even the most heavily disturbed areas.
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- Prairie lupine, a hardy, nitrogen-fixing plant was the first plant found on the Pumice Plain.
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- The plant innoculated by the gopher grew well and spread. [2 years after eruption]
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- The pyroclastic flow provided a unique laboratory for the study of below ground processes. [2 months after eruption]
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- Scientists wanted to determine how colonizing plants aquire important fungal and bacterial associations.
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- To determine if small mammals were agents of dispersal, a gopher was placed next to a lupine. [2 years after eruption]
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- The experiment revealed that gophers deposit beneficial fungi and bacteria in their droppings.
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- View of beneficial mycorrhizal fungi on lupine roots.
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- Root-like hyphae help mycorrhizae extract and deliver life-giving water and nutrients to plants.
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- Long-term studies are documenting the role of mycorrhizae and nitrogen-fixing plants in ecosystem development.
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- Lupine add nutrients to the pumice, trap seeds and aid the establishment of less hardy plant species.
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- Studies revealed that plants without the benefit of mycorrhizae faired poorly. [3 years after the eruption]
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- Scattered tree seedlings developed mycorrhizal associations from wind-dispersed spores. [5 years after eruption]
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- As vegetation spread, elk grazed the Pumice Plain depositing additional nutrients and seeds in their droppings.
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- The valley north of the crater was transformed by the eruption. [3 months after eruption]
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- No trace of the pre-eruption forest remained.
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- Scientists collected wind blown seeds to document plant establishment.
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- The prairie lupine was among the first plants to establish.
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- Insects that feed upon the plants soon followed, note aphids on lupine stem. [9 years after eruption]
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- Detailed long-term studies have documented important processed that influence plant succession. [15 years after eruption]
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- The once barren pumice has become a productive ecosystem. [17 years after eruption]
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- As vegetation develops, plant and animal diversity is increasing.
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- Thirty years after the eruption, plants have colonized much of the valley.
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- The Pumice Plain is a mosaic of developing trees, shrubs and meadow vegetation.
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- The Pumice Plain has provided an important laboratory for studying plant succession. [2 years after eruption]
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- Long-term studies are documenting the various physical and biological factors affecting plant succession.
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- Permanent plots have tracked the fate of individual tree seedlings. [6 years after the eruption]
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- Trees like this noble fir are gradually establishing across the valley.
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- Trees and shrubs are spreading across the Pumice Plain. [29 years after the eruption]
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- As vegetation developed, elk spent more time in the valley north of the volcano.
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- Elk rub their antlers on the young trees, killing their tops and retarding their growth.
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- Damage from elk browse and rubbing is negatively impacting tree establishment and growth.
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- Vegetation establishment has been slow on floodplains due to chronic disturbance.
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- Streams and wetlands fed by groundwater springs are stable and willows and Sitka alders are taking root. [29 years after eruption]
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- After 30 years, the Pumice Plain is a mixture of meadow vegetation and developing shrubs and trees.
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- Development of a new forest is being delayed by repeated browsing and damage from elk.
