Earth Science NotesVolcano Types

Factors Affecting Eruptions

• Trapped Gases– Carbon dioxide and water vapor get trapped

in magma and escape when pressure decreases

– Gases that build up a lot of pressure cause explosive eruptions

Factors Affecting Eruptions

• Silica – Silica is a compound composed of silicon and oxygen– Magma that is silica-rich is produces explosive

eruptions • Granitic magma• Found at subduction zones • Lava is more runny in consistency

– Magma that is silica-poor produces quiet explosions• Basaltic magma• Found at hotspots • Lava is thicker more viscous in consistency

Forms of Volcanoes

• Shield Volcanoes– Forms from the build up of quiet eruptions

through vents or fissures• Resembles a warriors shield

– Has gently sloping sides– Basaltic lava flows from here

Shield Volcanoes

Shield Volcanoes

Forms of Volcanoes

• Cinder Cone Volcanoes– Forms from the build up of explosive eruptions

• Bits of rock called tephra are blown into the air and fall to the ground. Over time the sides of this volcano forms

– Resembles a giant cone• Very steep side with loosely packed stone

Cinder Cone Volcanoes

Cinder Cone Volcanoes

Forms of Volcanoes

• Composite Volcanoes– Intermediate between cinder cone and shield

volcanoes– Eruptions vary some may be explosive others

quiet– Alternating layers of tephra and lava form the

sides of the volcano– Found near subduction zones

Composite Volcanoes

                                

composite volcano

Composite Volcanoes

Composite Volcanoes

Forms of Volcanoes

More Volcano Types

Features Of Volcanic Activity

• Batholiths – formed when magma cools underground

Features Of Volcanic Activity

• Volcanic Neck – magma inside volcano cools and outside is eroded away

Features Of Volcanic Activity

• Dike – magma that cools in vertical cracks

Features Of Volcanic Activity

• Sill – magma that cools in horizontal cracks

Features Of Volcanic Activity

• Caldera – top of volcano collapses on emptied magma chamber

                                                    

Photograph by M. Williams, National Park Service, 1977

Features Of Volcanic Activity

Volcanoes Destructiveness

Mount Vesuvius - 79 AD

Volcanoes Destructiveness• Mount St. Helen - Washington

Volcanoes Destructiveness

Volcanoes Destructiveness

This Diagram shows range of potential destruction

A super-eruption has the potential to cover the United States in 3 feet of ash from a plume. Pyroclastic flow would engulf the greater part of three states, and there is evidence that the last major 'super' eruption plunged the world into a freezing, volcanic winter that lasted a decade. An eruption would devastate world agriculture, severely effect the distribution of food and cause mass famine.

After the Aftermath

Summary

• Volcano Types– Shield / cinder cone / composite / others

• Features of Volcanic Activity– Intrusive Igneous Rocks (CH 5)

• Destructiveness of Volcanoes

• The Circle of Life