Eruption of Dormant Volcanoes?!?

What happens before, during and after a dormant volcano erupts? Can someone please help me? Thanks!

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  • Warren
    Lv 6
    9 years ago
    Favorite Answer

    Before: An eruption of a dormant volcano is usually preceded by a series of earthquakes and steam-venting episodes, caused by an injection of magma at shallow depth below the volcano. For example, Mount St. Helens remained dormant from its last period of activity in the 1840s and 1850s until March 1980 almost 155 years.

    During an eruption: During a volcanic eruption, lava, tephra (ash, lapilli, volcanic bombs and blocks), and various gases are expelled from a volcanic vent or fissure. There are three different metatypes of eruptions. Magmatic eruptions, involving the decompression of gas within magma that propels it forward. Second, Phreatomagmatic eruptions being the compression of gas within magma (the direct opposite of the process powering magmatic activity) and Phreatic eruption, which is driven by the superheating of steam via contact with magma;

    After an eruption:

    1-- The Santorini eruption (occurred between 1627 BCE and 1600 BCE), generated a 35 to 150 m (115 to 490 ft) high tsunami that devastated the north coast of Crete, 110 km (68 mi) away. The eruption devastated the nearby Minoan settlement at Akrotiri on Santorini, which was entombed in a layer of pumice.

    2-- Mount Pelée eruption (1902 dormant for over 100 years) is among the deadliest stratovolcanoes on Earth. The eruption killed about 30,000 people most deaths of which were caused by pyroclastic flows. (a fast-moving current of extremely hot gas of about 1,000 °C (1,830 °F)) and can travel at speeds generally as great as 700 km/h (450 mph). The eruption destroyed the town of Saint-Pierre killing 28,000 people.

    3-- Mt. St. Helens: A magnitude 5.1 earthquake centred directly below the north slope triggered part of the volcano to slide. The slide moved across Spirit Lake's west arm; part of it hit a 1,150-foot (350 m) high ridge about 6 miles (10 km) north. Pyroclastic flow material passed over the moving avalanche and spread outward, devastating a fan-shaped area 23 miles (37 km) across and 19 miles (30 km) long. In all, about 230 square miles (600 km²) of forest were knocked down,

    There is much information on the web concerning dormant and active volcanoes which can be gleaned for your edification. I hope I helped you.

    Regards,

    Warren

  • Anonymous
    9 years ago

    Mt. St Helen's erupted in May, 1980, not March. Geologists were aware that it was about to blow, because the magma chamber was inflating as indicated by inclinometers and levels on the flanks of Mt. St. Helen's. I received my B.S. in earth sciences/geology On May, 10, 1980 and Mt. St. Helen's blew a week later. An annular solar eclipse on commencement day May 10, 1994, excactly 14 years later, when I got my third bachelors degree, blew Mt. St. Helen's right out of the water in awesomeness. (The first degree was a B.A. with honors in history in 1975)

    Source(s): B.S. and M.S. in geology, B.S. in physical geography (1994), aborted M.S. in geophysics (all but thesis)
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