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. A bulge started to appear on the North side and it was increasing in size by about 1.5m a day. Scientists were really worried now. The eruption wouldn't take place from the crater but from this bulge. Pressure was rising and the bulge was growing. The danger zone they had marked out would be wrong and people in other locations were in danger.
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On the 18th May, 0830 hours, Ash and steam erupted. Two minutes later, an earthquake shook the mountain. This earthquake measured 5 on the Richter scale and also gave the bulge a move forwards and downwards. 1000's of tonnes of rocks, glaciers, ice, soil and mud raced downhill within a minute. It filled Spirit Lake and all the water in there was displaced and filled up the Toutle Valley. 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 ...

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