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Explain how/why the chemical composition (e.g. silica content) affects the eruptive style of a volcano.
Increase in silica content, more viscous magma, Eruptive style: Flow
What are the 3 common types of volcanoes?
- Cinder Cones
- Composite Cones
Describe characteristics of a shield volcano (shape/size, structure, magma composition, eruptive style, tectonic setting).
Broad, gentle sloping shape
Fluid basaltic lava
Made of layers of basalt
Very little pyroclastics or pyroclastic flow
E.g. Mauna Loa, Kilauea, Iceland
Tectonic Setting: Hot Spots
Describe characteristics of a Composite Cone (shape/size, structure, magma composition, eruptive style, tectonic setting).
Large, conical shape
Interbedded lavas and pyroclastics
Silica rich magma (doesn’t flow far), often of andesitic composition
Tectonic Setting: O/C Convergent Boundaries
E.g. Mt. St. Helens, Mt. Rainier
Describe characteristics of a Cinder Cone (shape/size, structure, magma composition, eruptive style, tectonic setting).
Generally a single event (thus small size)
Steep slope angle (30-40 degrees)
Built from pyroclastics (ejected lava fragments)
Occasionally may eject lava, usually from base
Gas-rich basaltic magma
Tectonic Setting: Anywhere there is a pocket, or chamber, of basaltic magma
What type of volcano is Mt. St. Helens?
What type of volcanoes is Mauna Loa?
What type of volcanoes are the Andes,?
What type of volcanoes are the Cascades?
Describe pyroclastic flows
Mix of ash and hot gas flowing down the volcano
Volcanic mud flows, ash mixed with water
What is the ophiolite complex
The structure of the oceanic crust
Describe and identify a Batholith
massive, discordant: irregular mass of intrusive igneous rock
Describe and identify a Dike
tabular, discordant: A sheetlike discordant igneous intrusion that cuts across layers of bedded country rock.
Describe and identify a Sill
tabular, concordant: sheetlike body formed by the injection of magma between parallel layers of preexisting bedded rock.
Describe and identify a Lacolith