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Mt St Helens Volcanic Eruption Case Study - Mount St Helens, Rocky Mountain Fold, North America.

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Mt St Helens Volcanic Eruption Case Study Where: Mount St Helens, Rocky Mountain Fold, North America. What Happened: On the 18th May 1980 at 0833 hours, Mt St Helens erupted. Seismologists studied beforehand and started to recognise that an eruption would occur soon. It first started when 100+ earthquakes were recorded from the 15th to the 21st of March. The earthquake that occurred on the 20th March 1980 gave scientists the early warnings of its first eruption since 1857. Although there were earthquakes recorded from the 15th, the tremor measuring 4.1 on the Richter scale on the 20th gave the signs of preparation for volcanic activity. What Happened (Continued): From the start of early May, Scientists started to notice something very unusual.


The water went further and reached Baker Camp and Portland Port on the Columbia River - All in a minute. At 0833 hours, the exposed magma exploded sideways sending out blast waves of Volcanic gas, steam and dust (called a nuée ardente). This all moved Northwards for 25KM and everything within this range: Animals and Vegetation, Buildings and houses were destroyed. Mt St Helens Spirit Lake after the eruption Why: A minor plate called the Juan de Fuca Plate (oceanic crust) started moving eastwards, colliding with the North American Plate which was also Oceanic crust. The Oceanic crust from the Juan de Fuca plate went below the North American Plate into the mantle. The extreme pressure and friction melted the crust and turned it to magma.


from the earthquake. The thicker ash rose 20km and drifted eastwards before settling. 1000's of people's homes or properties were damaged in some way or another. Some were incinerated, others had windows and cars damaged from ash all over USA. Spirit Lake was a lake that was seriously damaged from volcanic waste. Facts about Mt St Helens: 1314 feet was lost of the top of the Mountain The Landslide Debris Avalanche travelled at 150 miles per hour The lateral blast had 250 million cubic yards of waste and deposit The temperature of the blast was 350 degrees Celsius 24 megatons of thermal energy was released (7 megatons by blast the rest through release of heat) If all the lost timber was saved from the avalanche, it could build 150 000 houses, 4 bedroom houses. 185 miles of highways & roads and 15 miles of railways were lost in the blast.

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