Mount St Helens Research Paper

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Abstract The eruption of Mount St. Helens on May 18th, 1980 was largely due to a rockslide triggered by a M5.1 earthquake. This rockslide not only caused the depressurization of the cryptodome, resulting in the lateral blast and pyroclastic eruption, but evolved into a debris avalanche with a volume of 2.5km3 that caused destruction to a wide area surrounding the volcano. This rockslide/debris avalanche was the result of several events leading up to the May 18th earthquake. It left behind a hummocky, poorly sorted block-facies deposit and a long-lasting effect on the North Fork Toutle River valley and Spirit Lake. Introduction One of the most important events of the May 18th, 1980 Mount St. Helens eruption was the debris avalanche, the initial rockslide of which was a direct cause of the lateral blast and main eruption. Here, the events leading up to the debris avalanche, such as the cryptodome formation, the debris avalanche itself and the consequences of the event, such as the altitudinal elevation of Spirit Lake, are outlined in detail. The effects of the debris avalanche were mainly felt to the north of the volcano, as it was the north flank which failed. This report brings…show more content…
Over the next two months leading up to the earthquake, magma intrusion (Voight et al, 1981) formed of a cryptodome associated with a fracture network (Walter, 2011). Consequently, the volcano was destabilised due the intruding magma and additional hydrothermal fluids causing a loss of cohesion within the mountainside (Glicken, 1990). This destabilization was compounded by the intrusions leading to an increase in seismicity, resulting in a fracture network in the rock (Voight et al, 1981). However, without this loss of stability slope failure - and so the debris avalanche - may not have happened, as mathematical modelling of Mount St. Helens’ pre-eruptive state showed the volcano to be otherwise stable (Glicken,

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