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Mount St. Helens
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(FAQ 3) Did any life survive the 1980 eruption?
Although the ash-covered ground appeared lifeless after the May 18, 1980, eruption, scientists found that not everything had died. In fact, much to scientists’ surprise, thousands of plants, animals, and fungi survived in much of the disturbed area. These survivors ranged from single individuals to entire biological communities and ecosystems. Scientists discovered that the survivors, along with the thousands of dead trees and other dead organisms, played vital roles during ecological recovery.
Three distinct survival zones were created by the eruption
Living and dead organisms, termed “legacies,” were present throughout much of the disturbed area. Based on the types, amounts, and distribution of legacies, three distinct zones were apparent: zones where nearly all life was eliminated, zones of intermediate survival, and zones of widespread survival. Survivors produced seeds, spores, and offspring—these survivors initiated populations in adjacent areas where species did not survive. Dead trees, as well as surviving plants, provided food and habitat for colonizing animals and played many important ecological roles.
Scientists learned that four factors were critical for speciesí survival:
The time of day as well as season of the year helped some organisms survive. Nocturnal animals were below ground, for example, when the eruption began. At higher elevations, May is still late winter, and plant buds had not yet opened. Patches of snow and ice shielded some organisms from the searing heat and abrasion of the blast.
Rock outcroppings, cliffs, and ridges protected some areas from the brunt of the blast. Plants and animals in these sheltered sites had better chances of survival, whereas valley floors and terraces collected thick deposits of ash that smothered life.
Animals away at the time of the eruption (some salmon and migratory birds), in daytime retreats (bats, mice, voles), below ground (pocket gophers), or in water (trout and some amphibians) were protected and survived. Plants with dormant belowground buds had high survival rates.
Small animals such as deer mice (Peromyscus maniculatus), yellow-pine chipmunk (Tamias amoenus), and Trowbridge’s shrew (Sorex trowbridgii) tended to be in protected places, whereas large animals such as deer (Odocoileus spp.), elk (Cervus spp.), and bear (Ursus spp.) were exposed. The size factor affected tree survival also. Saplings buried in late-winter snowbanks survived, but large trees were toppled by the blast or scorched by the hot gasses.
US Forest Service - Pacific Northwest Research Station - Mount St. Helens