Lateral Blast
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- Pre-eruption view of Mount St. Helens and the magnificent forests and meadows on its north side.
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- Area north of the volcano before the eruption
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- Same view, three months after the eruption.
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- The lateral blast felled forests and transformed entire watersheds [3 months after eruption]
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- The lateral bast fragmented, uprooted and removed trees from Johnston Ridge.
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- On slopes facing the volcano like Johnston Ridge, the blast fragmented trees leaving only shattered stumps.
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- Shattered wood became part of the blast, shown here trapped in the safety cage of logging equipment 6 miles (10 km) away.
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- Damage from the lateral blast was greatest on ridges closest to and directly facing the volcano.
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- Further away trees were blown down like so many match sticks
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- The blast surged over ridges snapping off trees.
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- The blast skipped over steep ridges and rock out crops leaving sheltered pockets.
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- The scale of the blast area and downed trees amazed scientists. Circle the two scientists for scale.
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- The presence of large, blown down trees created numerous microsites in the blast zone.
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- The lateral blast created a complex mosaic of disturbance intensities.
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- Blown down trees with scientist for scale.
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- Scientists searched the 230-square mile blast area for signs of life.
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- Chance was important to survival, like these sprouts lifted and protected by the roots of a blown down tree.
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- By chance, some forest plants like this trillium survived.
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- Small trees and shrubs pressed flat under snow survived where large trees perished.
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- Surviving roots sprouted from eroded streambanks
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- Animals above ground and active at the time of the eruption perished.
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- Surviving snow-protected trees and shrubs [3 years after eruption]
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- A new subalpine forest takes hold [9 years after eruption]
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- Silver fir and mtn hemlock trees respond to ample sunlight [6 years after eruption]
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- Area is covered by trees and shrubs [15 years after eruption]
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- The forest canopy begins to close [14 years after eruption]
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- Logs are crushed to the surface by winter snow. [9 years after eruption]
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- Blowdown forest with no snow at time of eruption [3 years after eruption]
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- With ground contact, log decomposition increases. [15 years after eruption]
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- Trees and shrubs cover the disappearing logs. [24 years after eruption]
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- On steep slopes, plants survived where erosion exposed buried roots.
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- Streams were filled with downed trees and blast deposits [3 months after eruption]
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- Habitat conditions in streams were profoundly alterred. [3 months after eruption]
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- Eroded blast deposits were washed downstream. [3 months after eruption]
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- Formely forested streams were transformed into open, sediment-rich waterways. [2 years after eruption]
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- Temperatures were higher in blast zone streams.
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- Where ash was thin, roots of surviving plants sprouted.
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- A vigorous root system and rapid growth allowed fireweed to flourish.
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- Fireweed was quick to flower and spred seed across the blast area.
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- Pearly everlasting spread by producing underground stems and ample seed.
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- The blast zone contained a patchwork of standing forest and clearcuts.
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- Fireweed and other early successional plants spread rapidly.
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- The combination of surviving forest species and early successional colonizers produced diverse plant communities.
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- Remains of previous forest disappear, a new forest appears. [28 years after eruption]
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- The dense, rock-filled blast skipped over steep ridges and rock outcrops creating scattered sheltered pockets.
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- On cool, north-facing slopes, late lying snow sheltered small trees and shrubs.
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- The combination of snow protected survivors and colonizing plants produced high plant diversity.
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- Snow-protected fir and hemlock trees popped free of the ash, surviving where full sized trees perished.
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- Some lucky plants survived and sprouted from soil uplifted by blown down trees.
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- Fireweed and other early successional species sprouted from areas clearcut before the eruption. [3 months after eruption]
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- Fireweed and other early successional species sprouted from areas clearcut before the eruption. [3 months after eruption]
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- Same view showing fireweed, pearly everlasting, thistle and grasses. [4 years after eruption]
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- Fireweed produced large-quantities of light cotton-covered seeds that were dispersed by the wind.
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- Millions of fireweed seeds drifted onto the blown down forest. [2 years after eruption]
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- Same view, fireweed flourished during the fist decade after the eruption [6 years after eruption]
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- The combination of surviving forest plants and colonizing species has produced a diverse flora and fauna.
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- The combination of standing dead and downed trees and a thriving new forest has produced excellent habitat.
