Information Sheet for MT

Volcanic activity takes place when there is an unexpected or constant discharge of energy brought about by a surface or near-surface movement of magma.

The energy can be accumulated due to geothermal activity, earthquakes, fiery discharge of gases, and non-explosive excursion or incursion of magma. Pyroclastic Flow of Mt. St. Helens in 1980 Mt. St. Helens, which is the object of curiosity, exhibited some phenomenal volcanic activity in 1980.

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During the May 18, explosion of Mount St. Helens most of the pyroclastic flow was created when bulging heaps of inflated ash and rocks blew up to a few hundred meters like a spray above the internal crater and then broke through the open crater. The pyroclastic flows appeared before the vertical explosion column in the August 7 and July 22 blasts of Mount St. Helens. Each of the eruptive stages started with a spray of gases and pyroclasts from the mouth of the vent, which then produced a pyroclastic concentration current.

A Cross Section of Mt St Helens before the Eruption As shown in the diagram above, the earth which the mountain consisted of had the effect of suppresing the magma that was seeking its way out. Pressure of the magma was finally too high for the mountain to restrain and it exploded with considerable force through the rocks.Pyroclastic flows can be created in a number of ways. The usual acceptance is that the major cause of pyroclastic flows is gravitational crumbling of upright eruption columns. The transformation, as observed in the flare-up of Mt. St.

Helens, from expulsion of gases to the perpendicular column activity is believed to be brought about by an enhancement of the gas substances in the eruption spurt or a reduction in vent circumference with time (Branney, Kokelaar & Kokelaar, 2002). Enormous lateral explosion from Mount St. Helens on May 18 1980 affected territory within a 30 km radius from the central point of the volcano, uprooting and tossing giant trees as though they were matchsticks. The volcanic explosion moving at speed of up to 1100 km per hour demolished approximately 600 Sq KM of vegetation and structures. The intensely hot temperatures of gas and rocks in the pyroclastic current estimated to be between 200°C and 700°C ruined the entire area accessed by the flow. At Mount St.

Helens, the splurge emitted a powerful, North-directed tangentiaal discharge of ash, rock, and searing gases (Parchman, 2005). To the South, the destroyed area was smaller. It affected there only a small area down the slope from the peak. Together with older volcanic fragments, the explosion also comprised of the first magmatic substances created by the eruption of Mount St. Helens signifying that the avalanches and the resultant blast had uncovered the cryptodome magma.

Even though the lateral explosion started some time after the debris landslide, the blast’s speed was unprecedented and it soon passed the avalanche (Morris & Austin, 2003). The near-supersonic tangential explosion, laden with volcanic fragments, caused extensive damage on the territory as far as 1900 kilometers from the volcano. The fragments and mudflows from the volcanic activity of Mt. St. Helens reportedly obscured the Toutle basin to a depth of nearly 50 meters (Dale, Swanson, Crisafulli & Franklin, 2005).

Mt St Helens’ height was cut by over 1,300 feet because of the explosions that lasted for more than eight hours. Sadly, along with the numerous animals that were decimated, 57 individuals were reported dead because of the eruption (Carson, 2000). All visitors are cautioned not to walk around the mountain without a tour guide.