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GEOL105_9 - St Helens Aftermath Picture before the eruption...

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St Helens’ Aftermath Picture before the eruption  The north slope slid away – largest landslide observed After the volcano The summit was missing The entire north side of the volcano blown away  A little later Clearly shows devesation Sequence of events Magma starts moving in the volcano. The north side starts to bulge outwards in  response to the magma moving out towards the north side Earthquake occurs magnitude 5. Something. The bulge slides away – landslide.  Magma is at depth very underneath the volcano – north side of the volcano,  when the north slide moves away, the magma is released of pressures being  exerted on it. huge magma at depth, instantaneously, pressures are released  after landslide. The volcano was beginning to erupt as the landslide was  occurring. Lava dome – magma dome, because it was still within the volcano. Magma rising  up in a dome like configuration. Stages in mt st Helens The pressure inside the dome is released – some blasts vertically. The landslide  is moving down – after that, huge lateral explosion. 
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Shortly after the landslide, period of about a day – huge quantites of ash being let  out Map Surrounding area was devastated. There was an area about 220 square miles  completely devastated. Lahars – because there was a lot of snow and ice,  catastrophic melting of snow and ice caused lahars. Lahars flowing a large  distance away from the volcano.  Crater of the volcano (blue) – pyroclastic flows from the crater. A bit farther out –  trees in the region were burnt down. Several hundreds of km/ hr – lahar flow.  Bits and pieces of the forest left. 3.2 billion board of timber…  glass knocked trees down – huge trees, by lateral blast after landslide. Trees standing Everything else is blown down. Strange pathways as it moved through the forest. Mt st Helens may 18… The winds were blowing east, the ash was progressively moving out farther away  from the volcano. 9 – 10 hrs worth of ash transport due to the winds.  late morning – strange clouds… it started to rain, it wasn’t raining water – it was raining ash
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moses, eastern Washington… Yakima, central Washington gray, choking ash cloud… mt st Helens, june… a month after the volcano. Looked like the world’s largest ‘tooth quality’. There  was still some steam coming out of the volcano.
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