Table of contents
- Tectonic Setting and Volcanos Type of Mt. St. Helens, Nevado del Ruiz and Mt. Pinatubo
- Eruption History of Mt. St. Helens, Nevado del Ruiz, and Mt. Pinatubo
- Mt. St. Helens 1980 Eruption
- Nevado del Ruiz 1985 Eruption
This research paper is intended to travel through the history, composition, and destructive eruptions of three of the most well-known volcanoes on Earth in order to evaluate human preparedness in anticipation of Mt. Rainier's future eruption. Specifically, Mt. St. Helens, Nevado del Ruiz, and Mt. Pinatubo will be taken into consideration for the analysis. Additionally, a final overview of Mt. Rainier’s history will be presented and compared to the above-mentioned volcanos to establish if authorities' emergency plan regarding Mt. Rainier's next eruption could be considered adequate.
Tectonic Setting and Volcanos Type of Mt. St. Helens, Nevado del Ruiz and Mt. Pinatubo
Volcanos are one of the results of movements and interactions of tectonic plates within themselves. As stated by Doctor Ralph L. Dawes (2013), the Theory of Plates Tectonics explains how small fragments of the Lithosphere, the layer of the Earth we live on, can generate volcanos, earthquakes, and tsunamis by colliding and scraping against themselves. Land volcanos are created at a subduction zone in which the older and denser plate (Oceanic plate) subducts under the younger and less dense plate (Continental plate). As the Oceanic plate subducts, it reaches the Earth’s layer called the Mantle which is composed of very hot rocks. By adding water to the Mantle, magma is formed and the pressure created pushes the magma upwards until the Earth’s surface results in an eruption [1].
Mt. St. Helens is a volcano located in the US State of Washington declared active by geologists. It sits on the North American Plate and it is formed by the subductive interaction with the Juan de Fuca oceanic plate [2]. The second volcano was taken into consideration, Nevado del Ruiz is an active Colombian volcano that originated from the subduction of the Nazca oceanic plate to the South American plate [3]. Mt. Pinatubo is considered an active volcano as well and it is located in the Philippines. It is caused by the subduction of the Philippine Plate under the Eurasian Plate [4]. All three volcanoes are recognized as Stratovolcanoes. Stratovolcanoes are classified as such because of their well-known conic shape obtained after several eruptions layered their sides shaping their smooth figure [5].
Eruption History of Mt. St. Helens, Nevado del Ruiz, and Mt. Pinatubo
Mt. St. Helens started its eruptive activity about 275,000 years ago. Experts in the field identified four distinct stages of volcanic activity, spaced in time by intervals of non-activity of thousands of years or ka, which contributed to shaping the present Mt. St. Helens. The stages have been named Ape Canyon (275 to 35 ka), Cougar (28 to 18 ka), Swift Creek (16 to 12.8 ka), and Spirit Lake (3.9 ka to present) [6].
The most recent confirmed eruptions took place in 1980, 1989, 1990, and 2004 [7]. Compared to Mt. St. Helens, the other two volcanos had a slightly longer life. In fact, geologists confirmed that Nevado del Ruiz's first eruption happened in 6,660 BCE while Mt. Pinatubo’s in 7,460 BCE. The last eruptions registered are in 1985, 2012, and 2014 for the Colombian volcano and in 1992, 1992, and 1993 for the Philippine one [8][9].
Between those catastrophic events, the Mt. St. Helens eruption of 1980, the Nevado del Ruiz eruption of 1985, and the Mt. Pinatubo eruption of 1991 have been classified as some of the most destructive volcanic events ever recorded.
Mt. St. Helens 1980 Eruption
According to the U.S. Geological Survey or USGS (Michael Diggles, 2005), the volcano began showing signs of unrest on March 16th of the same year after several aftershocks hit the area and its diameter widened up to 1,300 feet in a week. At 8:32 a.m. of May 18th, 1980 an earthquake of magnitude 5.1 shook the earth detaching the summit of the volcano depressurizing the magma chamber, and generating intense explosions. Detritus of rock, ash, and lava were ejected into the air at a speed of 300 miles per hour and gas and steam were released into the atmosphere. The resulting cloud reached a vertical distance of 17 miles while the landslide traveled for 14 miles down the North Fork Toutle River before ending its triumphant course. The eruption reached its optimum momentum between 3:00 and 5:00 p.m. and thanks to constant winds 520 million tons of ash were blown 250 miles eastward from the volcano.
The such devastating eruption produced several volcanic hazards including landslides, lahars, ash clouds, and pyroclastic flows. Landslides covered an area of 23 square miles moving at a velocity between 70 to 150 miles per hour. Volcanic landslides or lahars reached a speed between 10 to 25 miles per hour damaging 27 bridges and approximately 200 houses. 0.26 cubic miles of ash were generated only at the time of the eruption. Pyroclastic flows eructed totaled 0.029 cubic miles falling at an estimated velocity ranging from 50 to 80 miles per hour and burning at a temperature of 1,300i Fahrenheit [10].
Nevado del Ruiz 1985 Eruption
According to Washington D.C: National Academy (Dennis S. Mileti, 1991), Nevado del Ruiz started its seismic and fumarolic activity on November 1984. On September 11th, 1985, a phreatic eruption, occurring when magma makes contact with water generating an explosion of steam, boiling water, ash, and rocks [11], took place. Ice and snow present on the summit of the volcano triggered the reaction which lasted for approximately six hours. In the coming months, the level of activity continued intermittently but was characterized by always less frequent events compared with the September 11th eruption. The situation did not change until November 10th when the continuous ground shakes interrupted an apparent calm situation. On November 13th, 1985, apparently with no premonitory signs of the imminent emergence, Nevado del Ruiz erupted at 3:05 p.m. The phreatic eruption freed ash and small rocks which started raining over Armero, a city located 28 miles from the volcano. At 9:08 p.m. a second eruption consisting of hot rocks came out violently from the summit of the volcano melting its ice cap and generating lava that streamed down in different lahars. These streams of lava and debris traveled at a velocity between 15 and 27 miles per hour covering a distance as high as 53 miles [12].
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