18.2 - Eruptions.

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Eruptions and Forms of Volcanoes

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Presentation transcript:

18.2 - Eruptions

Making Magma Activity depends on composition of magma Lava can be thin & runny or thick & lumpy

Magma Temperature Most rocks melt between 800-1200 °C In Crust & Upper Mantle Pressure Increase with depth because of weight of rocks High pressure increases melting temperature

Composition of Magma Amount of Gas & Silica Increase gas dissolved = increased explosiveness Dissolved gases = carbon dioxide, water vapor, sulfur oxide, sulfuric acid Water vapor determines where magma forms Water vapor decreases melting temperature

Composition Viscosity = Resistance to flow Temperature & silica content affect viscosity High viscosity = cool magma High silica = thick & sticky Traps gases, produces explosive eruptions Low silica = thin & runny Flow easily, produce quiet, non-explosive eruptions

Types of Magma - Basaltic Less then 50% silica content Low-viscosity magma Gas easily escapes Quiet eruptions Ex: Kilauea & Mauna Loa http://media-2.web.britannica.com/eb-media/31/20231-004-008EFA7E.jpg

Types of Magma - Andesitic 50-60% silica content Oceanic-continental subduction zones Intermediate viscosity Intermediate explosiveness Send high volumes of ash & debris Ex: Colima Volcano in Mexico http://images.livescience.com/images/050531_colima_volcano_04.jpg

Types of Magma - Rhyolitic More than 60% silica content Magma mixes with water and silica High viscosity Large volumes of gas trapped Very explosive

Explosive Eruptions If lava is too viscous to flow, pressure builds up until an explosion Tephra = pieces of solidified lava or pieces of crust Classified by size Ash = smallest tephra, diameter is less then 2 mm Blocks = largest tephra

Ash Can rise into atmosphere Tiny sulfuric acid droplets remain in stratosphere and block sun’s rays and decrease global temperature http://geology.com/articles/volcanic-ash/volcanic-ash-column.jpg

Pyroclastic Flows Tephra + gases VERY HOT http://vulcan.wr.usgs.gov/Imgs/Jpg/MSH/Images/MSH80_pyroclastic_flow_from_st_helens_crater_08-07-80.jpg

In-Class Assignment 18.2 Study Guide WKT