Earth Science 4th Quarter

VOLCANOES

VOLCANOES

Weak spots in the crust where magma (molten material) comes up to the surface.

Most are found over the subduction zones.

The word volcano comes from the Roman god of fire, Vulcan.

MAGMA

Magmar, I

choose You!!!!

FACTORS

That determine volcanic erruption

1. Magma’s temperature

2. Magma’s composition

3. Dissolved gasses

MAGMA TYPES

Composition Silica content

Viscosity Gas Content Tendency to form pyroclastics

Volcanic Landforms

Basaltic Least50%

Least Least1-2%

Least Shield dome,Basalt platform, Cinder cones

Andesitic Intermediate60%

Intermediate Intermediate3-4%

Intermediate Composite cones

Rhyolitic Most70%

Greatest Greatest4.1-6%

Greatest Volcanic domes,Pyroclastic flows

MAGMA’S COMPOSITION

Basaltic Tends to be fluid

Can travel a distance of 150km from the crater

Andesitic Volcanic roc composition is in between Basaltic

and Rhyolitic.

Rhyolitic Very viscous

Tends to create stream-like ribbon flows

OTHER COMPONENTS

Magma’s Temperature High – Fluid magma

Low – Viscous magma

Dissolved gasses75% - Water, 15% - Carbon Dioxide, 10% - other gasses

Silica Content Poor – More fluid, Gasses can escape easily

Rich – Traps gasses which may lead to explosive erruptions

EXTRUDED MATERIALS

Lava Magma without trapped gas

Comes from basaltic magma due to low silica content

Gasses

Pyroclastics

High silica content magma that forms from pulverized rock.

CONTINUATION

Ash ~ Formed when lava contains many bubbles

Pumice ~ Froth like structure

Lapilli ~ Walnut sized

Cinder ~ Pea sized

Blocks ~ Bigger than lapilli, Made from hardened lava

Bombs ~ incandescent (glowing) lava

VOLCANO TYPES

Cinnabar Island

SHIELD

Built from Basaltic magma

Broad dome shape

Example

Mauna Loa

CINDER CONE

Very steep, small (300m)

Made from pyroclastics

Collapses easily

COMPOSITE

Large, nearly symmetrical

Made up of interbedded layers of lava and pyroclasts

Examples

Mt. Mayon

Mt. St. Hellens