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Lecture_11_Lecture_Notes - Lecture 11 Outline Volcanic...

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1 Lecture 11 Outline Volcanic Terminology Volcanic Eruption Types/Sizes Volcano Types and Deposits Volcanology Volcanology: The study of volcanoes, volcanic rocks, and geological processes associated with volcanism VOLCANO TERMINOLOGY Vent: the opening through which the eruption takes place –“ Vents” - round –“ Fissure” - elongate Crater: the round or circular depression over a vent, typically within a volcanic cone Flanks: the sides of the volcano VOLCANIC ERUPTIONS Viscosity: A fluid’s resistance to flow. Low viscosity = easy to move (e.g. Hershey’s syrup) High viscosity = hard to move (e.g. Hershey’s hot fudge sauce) Viscosity is influenced by three factors: 1) Temperature: High T = Low Viscosity 2) S ilica (SiO 2 ) content of magma: High SiO 2 = High Viscosity 3) Volatile (gas) content High gas content = Low Viscosity In general, high viscosity magmas are more likely to produce large, explosive eruptions. Magma Type Viscosity Rock Formed Ultramafic Very low Komatiite Mafic Low Basalt Intermediate Intermediate Andesite felsic High Rhyolite
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2 Eruptive Violence: Three factors influence whether a volcanic eruption is violent (explosive) or passive (non-explosive) 1) Gas Content of Magma high gas = more explosive 2) Viscosity of the magma high viscosity build up big internal pressures and can be very explosive 3) Ratio of external water to magma during the eruption (moderate amounts of external water mix with magma and cause it to explode) VOLCANIC ERUPTIONS Two Main Types of Eruptions: 1) Passive Eruptions (Effusive) Lava Flows 2) Violent Eruptions (Explosive)
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Lecture_11_Lecture_Notes - Lecture 11 Outline Volcanic...

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