DYNAM EARTH FINAL REVIEW

DYNAM EARTH FINAL - Chapter 9 Volcanoes Made in Terra Hades…Volcanic Products • Lava Flows • Pyroclastic Debris • Volcanic Gas ← ← Lava

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Unformatted text preview: Chapter 9: Volcanoes Made in Terra Hades…Volcanic Products • Lava Flows • Pyroclastic Debris • Volcanic Gas ← ← Lava Flows • The ability of lava to flow depends on its viscosity • The more viscous a substance is the slower it flows o Water has a low viscosity o Honey has a high viscosity • The more silica the lava contains the grater its viscosity ← ← 3 types of lava flows • Highly viscous flow o Dome like shape (as it emerges) o Travels lit t le distance • Viscous Flow o Thick flows o Travels some distance • Fluid Flow o Thin flows o Travels great distance ← ← 2 types of eruptions • Explosive eruption (gray eruption) o Violent eruption in which material is primarily in the form of pyroclastic debris • Effusive eruption (red eruption) o More benign eruption in which material is ejected in the form of flowing lava ← ← *The more viscous a lava the more explosive the eruption • The more viscous the lava the more gas is trapped • As bubbles move from high to low pressure, their volume increases • Gas expands as magma rises and explodes the lava at the top • Greater the gas content, more explosive the eruption ← ← Volcano Geomorphology- shape and structure of volcano • Controlling Factors o Type of eruption o Type of flow ← *silica content - - viscosity - - gas content - - type of eruption ← *silica content - - viscosity - - type of flow ← Shield Volcanoes – broad, gently sloped cones • Silica content - low • Viscosity – low • Gas Content – low • Type of Flow – thin • Type of Eruption – effusive lava flows o Ex. Mauna Loa, Hawaii ← ← Cinder Cones – steep sloped piles of volcanic debris and some lava flows • Silica content – intermediate • Viscosity – intermediate • Gas content – intermediate • Type of Flow – thin • Type of Eruption – very explosive at vent; effusive lava flows o Ex. Cinder Cone, Arizona Stratovolcano (composite volcano) – very large cone- shaped mountaint • Silica content – high • Viscosity – high • Gas content – high • Type of flow – thick, dome • Type of eruption – explosive pyroclastic o Ex. Mount Rainier, Washington State • Alternating eruptions of pyroclastic material and effusive lava flows forms a “stratified” volcano • Steep-sided stratovolcanoes are prone to landsliding because of the alternating layers of hard rock atop loose sediment ← ← Typical Volcano • Crater – opening at the top • Summit vent – lava vent at the top • Flank vent – vent on the side • Magma Chamber – magma stored below ← ← Pahoehoe Flows – ropy surface texture ← ← Aa Flows – rubbly flow with jumbled angular pieces ← ← Pillows – blob like pieces formed under water ← ← 66-76% silica – silicic • intrusive – granite • extrusive - rhyolite ← 52-66% silica – intermediate • int rusive – diorite • extrusive - andesite ← 45-52% silica – mafic • int rusive – gabbro •...
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This note was uploaded on 05/05/2008 for the course EOS 11 taught by Professor Professor during the Spring '08 term at Duke.

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DYNAM EARTH FINAL - Chapter 9 Volcanoes Made in Terra Hades…Volcanic Products • Lava Flows • Pyroclastic Debris • Volcanic Gas ← ← Lava

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