Volcanoes

Volcanoes

An overview of volcano types, products, and hazards

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Types of VolcanoesA volcano is a vent in the

earth's crust through which lava, steam, ashes, etc., are expelled, either continuously

or at irregular intervals.

Volcanoes may be huge mountains or small cracks

and fissures.



Types of VolcanoesVolcanoes are the product of the tectonic activity underneath Earth’s crust as a result of convection in the mantle.





They are found especially at subduction zones, hot spots, and divergent mid-ocean ridges.

Types of VolcanoesVOLCANO TYPE VOCABULARY:

Active – The volcano is in a “current” eruption cycle.

Dormant – The volcano is “sleeping,” but may become active.

Extinct – Some volcanologists don’t use this term; the volcano is supposedly no longer

active and may be unable to become active.

Explosive -- Magma is more viscous and therefore retains the build-up of pressure

until the volcano erupts explosively. Usually a major hazard to those

around it when erupting…especially andesitic magma like on continents.

Non-explosive -- Magma is less viscous and allows gases to escape easier. Fluid

magma is possibly less of a hazard to those around it when erupting…

especially basaltic magma like hot spots or divergent mid-ocean ridges.




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Shield VolcanoNon-explosive eruptions of dark, fluid,

basaltic magma high in Fe and Mg. Low viscosity of the magma allows for the

flow off the mountain making the shield shape.

Example: Mauna Kea, Mauna Loa, Hualalai, and Kilauea which make up the “big island” of Hawaii.

Cinder Cone VolcanoNon-explosive eruptions ofbasaltic magma high in iron.Produces tephra (ash, dust,

rocks, & lava bombs). Steep sided with a conical

shape. Very common type of volcano.

Example: Paricutin, Mexico. This volcano erupted in a field in 1943.




Composite or StratovolcanoExplosive andesitic viscous magma rich in

silica that is layered with lava and rock from old eruptions.

Periods of inactivity followed by huge, violent explosions.



Examples: Mt. Rainier in Washington and Mt. Fuji in Japan





Some Volcanic Rock Formations

Mid-Ocean Ridge/Underwater

Divergent boundary produces usually fluid basaltic magma. Large rifts may erupt volumes of lava. Underwater pillow lavas may form.



Pillow lavas above,

Black smoker at mid-ocean ridge, &

Iceland erupts

Basaltic Lava Types

Pahoehoe is “smoother” lava at the surface, whileA’a lava is a rougher more viscous rocky lava that

crumbles as it flows.

A sampling of Hawaiian lava A’a crumbles over an older

pahoehoe flow

Volcanic ProductsGeologic products

include many types of igneous rock.

Also many formations that are volcanic in origin such as Devil’s Tower in Wyoming & Morro Rock in Morro Bay!



Projectile Volcanic Products

Ash, tephra, lava bombs, lapilli, pele’s tears, cinder, pumice, and other volcanic products may be ejected through the air.




Other Volcanic HazardsPyroclastic flows of

HOT ash, rock, and debris move quickly down the slope.

Lahars are mud flows from either rains after eruptions or flash melted snow/glaciers that carry ash and debris.

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Volcanoes

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