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Mount Saint Helens |
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| Before the 1980 Eruption | ||||||||||||||
| In the beginning, Mount Saint Helens' lava was composed mostly of silica, about 2,500 years ago the lava became mostly mafic (Topinka, 2000). The rocks found from the early volcano include andesite and dacite Topinka, 2000), it also created Pyroclastic deposits, tephra, domes and short lava flows (Topinka, 2000). The volcano after 2,500 years ago had some of the same rocks erupted but also produced basalt and hot lahars (Topinka, 2000). | ||||||||||||||
| 1980 Eruption | ||||||||||||||
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| After the 1980 Eruption More Eruptions There were more smaller eruptions that followed this massive eruption. The next eruption was on May 25, 1980, followed by another eruption on June 12, this produced a small lava dome inside the crater (Shane, 1985). The lava dome was about 140 feet high and 1,200 feet in diameter. The next eruption was on July 22, this basically destroyed the lava dome from the last eruption (Shane, 1985). On the next eruption on August 7, a new lava dome was built only to be destroyed by another eruption on October 16 (Shane, 1985). Other small eruptions throughout the next couple of years added to the lava dome in the crater. Between the years of 1987 and 2004 the mountain was relatively quiet, was a few minor events (Topinka1, 2005). Because the mountain was so quiet, a glacier formed in the crater and partly on top of the lava dome (Topinka1, 2005). On September 23, 2004 many shallow earthquakes happened under and in the lava dome (Topinka1, 2005). This turned attention to the mountain once again. By the next day there had been hundreds of earthquakes (Topinka1, 2005), and by October 1st earthquakes were happening practically continually. At the same time, scientists noticed that the glacier in the crater was cracking (Topinka1, 2005), this meant that magma was coming up towards the surface. From October 1st to October 5th small eruptions happened and threw ash about half a mile across the glacier (Topinka1, 2005), but the only explosion that reached a populated area was the last one on October 5th. The mountain has quieted down since then. Since the eruptions in late 2004, the mountain started to form a welt next to the lava dome (Topinka1, 2005).
Landscape/Vegetation The eruption killed off most of what was in the area, especially on the north side. There were different kinds of wreckage, these were divided into different zones (USDA Forest Services, 2005), these zones are described below.
For the first five years the only vegetation was from the plants that had survived the eruption and were able to grow through the rock and ash above it (Frenzen, 2000). Since the eruption, plants have been able to re-grow and have been able to spread out. The variety of plants has also grown, through the use of wind spreading seeds (Frenzen, 2000). As time goes on, the blast zone will recover, as long as there are no more eruptions soon. Wildlife While it looked like the eruption decimated everything in its path, scientists found many animals survived (USDA Forest Services, 2005). Birds: Any birds that were inside the blast zone (230 square miles) were killed, but outside of this zone, birds survived (Frenzen, 2000). Since birds have the power of flight, within days, birds were already re-habiting the blast zone (USDA Forest Services, 2005). Birds were easily able to reconstruct their habitats. In the years following the eruption more birds have come back as the vegetation comes back (USDA Forest Services, 2005). Mammals: Roughly half of the smaller mammals survived the eruption (Frenzen, 2000). Generally in the areas that received a thicker blanket of debris and ash did not have animals survive while the areas that got less debris and ash had mammals that survived ((USDA Forest Services, 2005). Smaller mammals like the northern pocket gopher were able to survive because they lived underground (Frenzen, 2000). Most of the smaller and midsized mammals were able to return within 10 years of the eruption in 1980 (USDA Forest Services, 2005). Large mammals also had a hard time after the 1980 eruption. All large mammals within the blast area that could not outrun the explosion were killed (USDA Forest Services, 2005). The only place larger mammals were able to survive was in the tephra-fall zone (USDA Forest Services, 2005), but they had to migrate out of the area to find food. Because large mammals are able to move greater distances, these animals soon returned to the blast zone is search of food (USDA Forest Services, 2005), and within about 5 years many of the large mammal populations were back up in the several hundreds. Fish: Before the eruption the lake had around 26 species of fish (USDA Forest Services, 2005). Fish survival varied depending where the body of water was located. Most fish in the blowdown zone had survived, mainly attributed to the fact that these lakes were partially frozen (USDA Forest Services, 2005). Because of all of the debris that went into Spirit Lake, all of the fish here died out (USDA Forest Services, 2005). The first fish in Spirit Lake was found in 1993, and a second was found in 1994 (Frenzen, 2000). It took over a decade for fish to return here. The rivers in the area were flooded with ash and as a consequence, most of the fish here were killed (USDA Forest Services, 2005). Amphibians: Many amphibians survived the eruption, and the species that had the best survival rate were those that lived in water (Frenzen, 2000). It was only the amphibians that lived on land, and above ground, that suffered the most (USDA Forest Services, 2005). Because of the high survival rate of amphibians and their ability to move great distances, they were able to repopulate areas quickly (Frenzen, 2000) and within one year amphibians began to inhabit new ponds (USDA Forest Services). This species had one of the quicker bounce backs. Reptiles: There were very few reptiles in the Mount Saint Helens area prior to the eruption, only about 4 species (USDA Forest Services, 2005). After the eruption reptiles were not seen much. The only places reptiles were seen were in areas that only received ash (Frenzen, 2000). Since the eruption only garter snakes and the northern alligator lizard have been recorded (USDA Forest Services, 2005). Since the affected areas became less populated with trees, the few reptiles that lived in the area were able to dramatically increase their numbers (USDA Forest Services, 2005). Once the area is able to become more dense, the reptiles will no longer be able to survive in the numbers they have. Insects: Insects suffered a great deal from the eruption. Insects in the blast zone as well as in the places were ash fell. (Frenzen, 2000). The biggest problem with survival was the lack of moisture, another problem was that the ash clogged their pores, which they use to breathe (Frenzen, 2000). It took years after the explosion to get insects back up to their pre-eruption numbers (Frenzen, 2000).
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