In the northern Pacific sits a vast system of volcanoes. The Ring of Fire is home to hundreds of behemoths that terrorize the lands surrounding them. Mount St. Helens are one of these beasts, wreaking havoc on Washington and being the most active in the last 10,000 years.
Located in Skamania County, Washington this composite (stratovolcano) is highly active, and has been an interest of scientists for years. According to the USGS, it was created by the submerging of the Juan de Fuca Plate under the North American plate around 40,000 years ago. It is part of the Cascade Mountain Range which includes nearly 20 volcanoes and 4,000 separate volcanic vents on the Cascade Volcanic Arc. At the base, its elevation is 4,400 feet, and everywhere else is approximately 4,000 feet, and is 5,000 feet tall. It has a diameter of six miles, with a volume of ~17.2 cubic miles.
Washington is very mountainous and covered in trees. It has “oddly hummocky terrain” and “is covered with a patchwork of vegetation and small ponds” (Perkins). There were about 4 miles of tree-line before the eruptions that wiped it away from the pyroclastic flow. The elevation is steep with a wide crater from the 1980 eruption. It is relatively young compared to the surrounding volcanoes, with the summit cone rising 2,200 years ago. The closest volcano to Mount St. Helens is 45 miles west, Mount Adams, which is regarded as the “brother/sister” volcanic mountain to Mount St. Helens.
The name derived from a British diplomat Lord St. Helens with George Vancouver who surveyed the mountain in the 18th century. It was later nicknamed “Fuji-San of America”. It’s most well-known for its ash explosions and pyroclastic flows. “Silicic volcanoes are famous for capricious behavior…” (Iverson, et al 439). The materials that come from this volcano range from lahars, avalanches of snow and rock, pyroclastic density, mows, ballistic projectiles and pulverized, recycled existing debris flows. In one eruption, the volume of rock that erupted was 25 cubic kilometers and deposited over 100 kilograms of tephra including; pumice, glass shards, crystals and different minerals and shattered igneous, metamorphic and sedimentary rock. In none of the eruptions, however, were there any magma, but superheated groundwater which makes it a highly viscous volcano. This makes the volcano extremely explosive when it erupts. The stratigraphy of the volcano is around 50-60 miles away from it, with tephra layers deposited since it first started to erupt.
Below are rocks consisting of andesitic, deictic, and basaltic layers that can be aged around 50,000 years old. “[It] has been thoroughly mapped and characterized by previous workers” (Severs, et al 441). The minerals that are highly associated with this volcano are pyroxene crystals with iron and magnesium diffusion.
The last notable eruption of Mount St. Helens was in May 1980. It was the last eruption since the 1915 eruption of Lassen Peak in California and preceded by two-month series of earthquakes and steam venting episodes. On May 18th, the entire north face of the volcano slid away from an earthquake “expos[ing] a subsurface lava ‘cryptodome’” (Berlo, et al). It was caused by the injection of magma at shallow depth below that created a huge bulge and fracture system on the north face. This caused a hot mix of lava and pulverized older rock toward Spirit Lake so fast that it overtook the avalanching north face. The eruption column rose around 80,000 feet and deposited ash in 11 US states and five Canadian provinces. Snow, ice, and entire glaciers on the volcano melted, creating lahars, which later “heightened public awareness of inherent instability of high, snow-covered volcanoes, where even small eruptions can almost instantaneously melt large volumes of snow” (“Mount St. Helens”). These lahars reached Columbia River about 50 miles southwest of Mount St. Helens. This eruption killed game and 57 people and caused approximately 1 billion dollars in damage, which is around 2.88 billion dollars in today’s economy. It incited the NIOSH (National Institute for Occupational Safety and Health) “…to collect a number of settled dust samples from several areas within the State of Washington and determine the presence and quantity of respirable crystalline silica” (Dolberg, et al 53). This eruption was followed by less destructive eruptions later in the same year.
This volcano is well known for consistent dome building. The release of pressure caused steam and ash to emerge in 2004, which was accompanied by a 2.5 magnitude earthquake. In 2006, the “fin” or “slab” was being forced upward six feet per day and it began crumbling in frequent rock falls, even as it was still being extruded. Later in 2006, white plumes emerged, but this was caused by the constant lava extruding in the crater. In 2008, there was another small “eruption” that was comparable to the 2004 one, with some seismic activity. Later in 2008, Mount St. Helens went quiet, and after 6 months it was determined that the long eruption had finally ended.
Mount St. Helens is a behemoth that has been an interest for years. The volcano has given us more recent evidence of volcanic activity and the ability to record the behavior. The volcano has been highly eruptive in the past 10,000 years, more than any other volcano in the Cascade Mountain Range and Volcanic Arc. It is highly comparable to Mount Fuji, with many similar destructive characteristics. It is large, looming, and absolutely scary to see in action, but a beautiful masterpiece of earth’s creations.
Works Cited
Berlo, Kim, et al. "Geochemical precursors to volcanic activity at Mount St. Helens, USA.” Science 306.5699 (2004): 1167+. <Journal Link>.
Dollberg, Donald D., Michele L. Bolyard, and David L. Smith. "Evaluation Of Physical Health Effects Due To Volcanic Hazards: Crystalline Silica In Mount St. Helens Volcanic Ash." American Journal Of Public Health 76. (1986): 53-58. <Article Link>.
Iverson, Richard M., Daniel Dzurisin, and Cynthia A. Gardner. "Dynamics Of Seismogenic Volcanic Extrusion At Mount St Helens In 2004-05." Nature 444. (2006): 439- 443. <Article Link>.
"Mount St. Helens." Environmental Encyclopedia. Gale, 2011. <Reference Link>.
Perkins, Sid. "A Fresh Look At Mount St. Helens." Science News 177.9 (2010): 18-21. <Article Link>.
Severs, M.J., et al. “Investigation Of Long-Term Geochemical Variations and Magmatic Processes At Mount St. Helens.” Geofluids 13.4 (2013): 440-452. Print.
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