Mt St Helens

Miriam Juhl MW 815 Mount Saint Helens Having lived in a valley the majority of my life I can understand all too easily what it is to take the mountains around you for granted. In ignorance of their formation, unaware of how their past or future may affect me, or my community. That is just how the inhabitants of Portland were before Mount Saint Helen’s awoke from a long slumber some 30 years ago. Luckily for me, the volcanism responsible for my mountain ranges are truly long dormant. The tectonic forces driving their formation no longer in action. Unbeknownst to the majority of Portlandians pre-March 1980, the snow-capped symmetrical beauty lying picturesquely 50 miles in the visible distance was in actuality a slumbering monster.

One that had many times over wreaked havoc on the surrounding land, it’s scarring visible through the timber. Part of the majestic Cascade Mountain Range; which spans 700 miles through North America’s Pacific Northwest from California to British Columbia, Mount Saint Helens is a stratovolcano located 96 miles south of Seattle, in Skamania County, Washington. It’s formation being directly driven by volcanism as a result of the Juan De Fuca plate subducting beneath the North American plate. Mt St Helens is notoriously famous or its May 18th, 1980 eruption; a deadly event bestowing the Mountain with the title of single most destructive volcanic eruption in US history. Inhabitants of the area were first warned of the volcanos impending eruption in March of 1980 where on the 16th of that month Mount Saint Helens experienced a series of earthquakes.

March 27th that year the Mountain shook the surroundings with its first eruption in a century, this was the beginning of both seismic and volcanic activity that would stretch on for months culminating in the fatal eruption of May 18th which claimed 57 lives. It wasn’t the size of the eruption or the lava flows that made this eruption so devastating, but the consequent debris flows that mercilessly tore through anything in their path. In comparison, even in its own history, Mount Saint Helens eruption that fateful day was quite small in regards to total output, which was a third of a cubic meter. Time is immense, and this mountain dates back millennia. Long before 1980, 275,000 years ago to be exact, Mount Saint Helen’s began an ascension to a deadly volcano, its age measured in stages. The mountain started out as domes in the Ape Canyon Stage (275-35 ka) during which time there were two major eruptive times with a long hiatus separating them these are responsible for the earliest deposits that have been measured. Between each stage of activity is a time of dormancy.

The Cougar Stage (28-18 ka) is believed to be the most active stage being marked by the Swift Creek flow (18 ka) the largest lava flow in the history of the mountain. This was followed by the Swift Creek Stage (16-12.8 ka) which although of short duration was marked by two phases. The Spirit Lake Stage (3.9 ka-present) is separated into seven periods of eruptive activity and brings us into the present day. Each eruptive period contributed to the many depositions found. During the Smith Creek (3.9-3.3 ka) saw an eruption four times that of 1980. Through every period it is clear to see that Mt St Helens most threatening geologic hazard is consistently debris flows associated with highly volatile volcanism. Through its long history, the volcano has shown us it’s fury and we know more is yet to come.

The probability of Mount St. Helens resuming activity is unquestionable, how and when present the questions. Many probabilities include the growth of new lava domes, eruptions of both basaltic and andesitic tephra, lava flows, explosive eruptions of tephra, large lahars, and pyroclastic flows. With today’s technologies, massive stores of data and computing power we are better equipped to face what Mount Saint Helen may want to throw at us. Teams of volcanologists, geologists and scientists are closely monitoring the Mountains activity.

And yet even with all of this, it’s hard to say what to expect next, or when. All that can be said with certainty is that we have yet to see the end of what this volcano can and will do, but whatever it may be, we will not face it unaware. Citations: Science for a changing World, USGS. “Volcano Hazards Program.” What Is an Earthquake and What Causes Them to Happen?, 2018, www.usgs.gov/volcano/mount-st-helens. Oregon State University. ‘New imagery solves mystery of why Mount St. Helens is out of line with other volcanoes.’ ScienceDaily. ScienceDaily, 4 September 2018. . ‘Saint Helens, Mount.’ The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. 12 Nov. 2018 . “’NO ERUPTION’ at Mount St. Helens but dust and ash, warning says”. F. Zarkhin. The Oregonian/OregonLive. 14 Oct.2018. https://www.oregonlive.com/pacific-northwest-news/index.ssf/2018/10/no_eruption_at_mount_st_helens.html https://pubs.usgs.gov/fs/2000/fs036-00/ https://volcanoes.usgs.gov/volcanoes/st_helens/ https://faculty.washington.edu/moral/publications.html