Earth Science NotesVolcanic Eruptions

Our Objectives Today are…

I can …

•Explain the Factors that affect Volcanic Eruptions

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

•Describe the destructiveness of Volcanoes

•The Circle of Life

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• Gases build up

more pressure in thicker (more viscous) magma.

• What type of magma would cause the greatest explosion.

Recall: Unit 3 Viscosity means RESISTANCE TO FLOW

Factors Affecting EruptionsSilica Content • Silica is a compound composed of silicon and oxygen

• Magma that is silica-rich (i.e. Granitic) produces explosive eruptions – Has a high viscosity (THICK) – TRAPS more gasses – RECALL: silica-rich magma formed granitic (felsic) rocks

Factors Affecting Eruptions

Silica Content • Silica is a compound composed of silicon and oxygen

• Magma that is silica-poor (i.e. Basaltic) produces quiet explosions– Has a LOW viscosity (Thin) – Forms nonexplosive eruptions – RECALL: silica-poor magma formed basaltic (mafic) rocks

Hawaiian Volcano

Basaltic Andesitic Granitic (Rhyolitic)

Factors Affecting Eruptions

• Low Viscosity (Basaltic) Magma– https://www.youtube.com/watch?v=qTTLYx4X

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• Higher Viscosity (Granitic) Magma– https://www.youtube.com/watch?v=e4PUOBI

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Volcanic Eruption Types• Volcanic

eruptions are characterized by expolosivity and height of plume.

Please Note: as with classification scheme, there are several forms and eruptions may be difficult to distinguish at times

Volcanic Eruption Types

Four Main categories of volcanic eruptions(see EN: Kinds of Eruptions)

• Hawaiian – weakest

• Strombolian – weak

• Vulcanian – kind of explosive

• Pelean – massive explosions

Volcanic Eruption Types

Hawaiian Eruptions

https://www.youtube.com/watch?v=CSu_netRm8E

Volcanic Eruption Types

Strombolian Eruptions

https://www.youtube.com/watch?v=w-S57sd7j9Y

Volcanic Eruption TypesVulcanian Eruptions

https://www.youtube.com/watch?v=YF7ib5ToVs4

Volcanic Eruption Types

• Pelean Eruptions

Volcanic Eruption Types

• Even Larger than a Pelean Eruption are Plinian Eruptions https://www.youtube.com/watch?

v=IETUa_nOk1g

Volcanoes Destructiveness

Mount Vesuvius - 79 AD

Volcanoes Destructiveness• Mount St. Helen - Washington

Volcanoes Destructiveness

Features Of Volcanic ActivityLimnic Eruptions: Lake Nyos

Features Of Volcanic ActivityLimnic Eruptions: Lake Nyos

• Lake Nyos is a deep lake high on the flank of an inactive volcano in Cameroon.

• A pocket of magma lies beneath the lake, charging the water with an estimated 90 million tonnes of carbon dioxide (CO2).

• In 1986, a limnic eruption at Lake Nyos triggered the sudden release of about 1.6 million tonnes of CO2 that rushed down nearby valleys, displacing all the air and suffocating approximately 1,700 people within 20 km of the lake.

Features Of Volcanic ActivityLimnic Eruptions: Lake Nyos

Elements for a Limnic Eruption

• Very deep volcanic lake.

• Lake has to be over a slow source of volcanic gas.

• Lake has to be very, very still.

Features Of Volcanic ActivityLimnic Eruptions: Lake Nyos

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

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

Features Of Volcanic Activity

Our Objectives Today were…

Can I …

•Explain the Factors that affect Volcanic Eruptions

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

•Describe the destructiveness of Volcanoes

•The Circle of Life