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Western Carolinian Volume 69 Number 06

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  • WCnewsmagazine 7 Mount St. Helens poised for eruption? 1, Jennifer wikey Vancouver! Vancouver! This is it! Those were the last words of 30-year-old geologist Glenn Johnson as the volcano he was standing on, Mount St. Helens, erupted for the first time in more than a century, killing fifty-seven people and demolishing 600 square kilometers of forest. Twenty-four years later, increased activity at the usually quiet Washington mountain has scientists acknowledging the possibility of another eruption. This does not come as a surprise to volcanologists, however, as Mount St. Helens is currently in what is considered its Modern Eruptive Period (which began with the explosion in 1980). Mount St. Helens May 18, 1980 eruption was triggered by a magnitude 5.1 earthquake about one mile beneath the surface of the volcano. The violent initial explosion produced a mushroom-shaped column of ash, called the lahar, that reached about 80,000 feet in less than fifteen minutes and scorched 200 square miles of land. Ash rained over an area of 22,000 square miles, returning the early Washington morning to night-like darkness. The pyroclastic flowor ground- hugging avalanche of 1,300-degree ash, pumice, rock fragments and volcanic gasrushed down the side of the volcano at speeds of 50 to 80 miles per hour, devastating six square miles. At the time of the blast, the north face of the mountain collapsed in a massive rock and debris slide that destroyed nearly 230 square miles of forest. The eruption was nine hours in duration, but it dramatically changed Mount St. Helens and the surrounding landscape within moments. It is the worst volcanic disaster in the recorded history of the United States. Another eruption occurred at Mount St. Helens in 1986, but it was nowhere near the intensity of the 1980 event. The volcano roared back to life again on the morning of September 23, 2004 with a swarm of very small, shallow earthquakes (less than magnitude 1) that peaked in intensity on September 24 and then slowy declined again. Between September 25 and 26, the character of the swarm changed yet again, producing 190 earthquakes, ten of which were magnitude 2-2.8. This is the most large earthquakes in a twenty four hour period since the eruption of October 1986. Immediately after a small steam emission on the afternoon of October 2, seismic activity in the volcano changed from mostly rock breakage events to a continuous low-frequency harmonic tremor which lasted for 50 minutes. This is indicative of magma movement, according to the United States Geological Survey. Consequently, in a press release later that day, the USGS declared We are increasing the alert level to Volcano Alert [Level 3], the highest alert level, indicating that an eruption could be imminent. Authorities evacuated visitors from a five-mile radius around the mountain over that weekend. Activity at Mount St. Helens died back down, however, and on October 6, the alert level was lowered to Volcano Advisory, or Alert Level 2, where it remains as of October 18. Interestingly, Mount St. Helens destructive 1980 eruption was preceded by two months of intense earthquakes and intermittent, weak eruptions. A similar pattern of increased seismicity is being seen now, according to Nick Allmendinger, assistant professor of geology at WCU. You can call an increase in seismicity an increase in ee or magnitude of earthquakes, says Allmendinger, and they're seeing USGS USGS Photo by Austin Post,May 18, 1980 oth. Seismic activity at Mount St. Helens is currently low to moderate, compared to e late September. According to the USGS, small earthquakes are occurring at a rate of one every five to ten minutes, with the largest magnitudes only about 1.5 on the : Richter Scale. The ongoing intermittent steam emissions, or phreatic eruptions, are Mount Saint Li caused by molten rock melting the ice that covers the mountains peak and produce no lava flow. So is it going to erupt again? The possibility has not been ruled out. As a result of the intense unrest of the past two weeks, we infer that magma is at a very shallow level, reads the USGS October 11 Mount St. Helens update. We expect fluctuations in the level of unrest to continue during coming days. Escalation in tf degree of unrest and perhaps an eruption could occur suddenly or wit warning. _. For more information about Mount St. Helens, vi website at http:/Avcuvax1.weu .edu/%7 Eallmendinge:
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