Earth Science Notes Volcanic Eruptions Our Objectives Today

Earth Science Notes Volcanic 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 Eruptions Silica 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=q. TTLYx 4 X o 2 k • Higher Viscosity (Granitic) Magma – https: //www. youtube. com/watch? v=e 4 PUOBI w. Ev 0

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_n et. Rm 8 E

Volcanic Eruption Types Strombolian Eruptions https: //www. youtube. com/watch? v=w. S 57 sd 7 j 9 Y

Volcanic Eruption Types Vulcanian Eruptions https: //www. youtube. com/watc h? v=YF 7 ib 5 To. Vs 4

Volcanic Eruption Types • Pelean Eruptions

Volcanic Eruption Types • Even Larger than a Pelean Eruption are Plinian Eruptions https: //www. youtube. com/watch? v=IETUa_ n. Ok 1 g

Volcanoes Destructiveness Mount Vesuvius - 79 AD

Volcanoes Destructiveness • Mount St. Helen - Washington

Volcanoes Destructiveness

Features Of Volcanic Activity Limnic Eruptions: Lake Nyos

Features Of Volcanic Activity Limnic 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 (CO 2). • In 1986, a limnic eruption at Lake Nyos triggered the sudden release of about 1. 6 million tonnes of CO 2 that rushed down nearby valleys, displacing all the air and suffocating approximately 1, 700 people within 20 km of the lake.

Features Of Volcanic Activity Limnic 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 Activity Limnic 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

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