Chapter 12 - Volcanoes

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Transcript Chapter 12 - Volcanoes

Grotzinger • Jordan Understanding Earth Sixth Edition

Chapter 12:

Chapter 12

Volcanoes

About Volcanoes

• Volcanoes are windows through which we can see the interior of the Earth.

• Volcanoes help us understand the plate tectonic process and mantle convection. • Volcanoes are also connected to Earth’s atmosphere and hydrosphere.

Lecture Outline

1. Volcanoes as geosystems 2. Lavas and other volcanic deposits 3. Eruptive styles and landforms 4. Interactions of volcanoes with other geosystems 5. The global pattern of volcanism

Lecture Outline

6. Volcanism and human affairs

1. Volcanoes as Geosystems ● Parts of the volcano ● hill or mountain made of: ● lavas ● other erupted materials

1. Volcanoes as Geosystems ● Parts of the geosystem ● rocks ● magmas and lavas ● processes of melting and eruption

Pipe Side vent Central vent Lava flows

Volcanic geosystem

Lithosphere Magma chamber

Pipe Side vent Central vent Lava flows

Volcanic geosystem

Lithosphere Magma chamber Magma, which originates in the asthenosphere...

Pipe Side vent Central vent Lava flows

Volcanic geosystem

Lithosphere Magma chamber ...rises through the lithosphere to form a crustal magma chamber.

Magma, which originates in the asthenosphere...

Pipe Side vent Lithosphere Magma chamber Central vent Lava flows

Volcanic geosystem

Lavas erupt through a central vent and side vents,...

...rises through the lithosphere to form a crustal magma chamber.

Magma, which originates in the asthenosphere...

Pipe Side vent Lithosphere Magma chamber Central vent Lava flows

Volcanic geosystem

...accumulating on the surface to form a volcano.

Lavas erupt through a central vent and side vents,...

...rises through the lithosphere to form a crustal magma chamber.

Magma, which originates in the asthenosphere...

1. Volcanoes as Geosystems ● Functions of the geosystem ● volcanic plumbing systems ● volcanoes as chemical factories

Thought questions for this chapter

Give a few examples of what geologists have learned about Earth’s interior by studying volcanoes and volcanic rocks.

2. Lavas and Other Volcanic Deposits ● Types of lava ● basaltic lavas (1000  1200ºC) ● aa ● pahoehoe ● pillow lavas

Pillow lavas on the sea floor

2. Lavas and Other Volcanic Deposits ● Types of lava (

continued

) ● andesitic lavas (<1000ºC) ● rhyolitic lavas (600  800ºC)

Mt. St. Helens’ andesitic cone

2. Lavas and Other Volcanic Deposits ● Texture of volcanic rocks ● reflect conditions under which they crystallized or formed ● vesicles (bubble holes) ● glassy texture (no crystals) ● pyroclasts (broken pieces)

Vesicles in basalt

2. Lavas and Other Volcanic Deposits ● Texture of volcanic rocks ● pyroclastic deposits ● volcanic ejecta (ash, bombs) ● pyroclastic flows (volcanic tuffs and breccias)

Arenal, Costa Rica: pyroclastic eruption

Volcanic ejecta bomb

Volcanic tuff

Volcanic breccia

Mt. Uzen, Japan: pyroclastic ash flow

2. Lavas and Other Volcanic Deposits ● Eruptive styles and landforms ● central eruptions ● shield volcanoes ● volcanic domes ● cinder cones ● stratovolcanoes ● volcanic craters ● calderas ● diatremes

Eruptive styles

Crater Lake, Oregon

Ship Rock, New Mexico Diatreme

Diatreme (Ship Rock)

2. Lavas and Other Volcanic Deposits ● Eruptive styles and landforms ● eruptions from linear cracks ● fissure eruptions ● flood basalts ● ash-flow deposits

Fissure eruption: Laki fissure, Iceland

Sequence of events: formation of a fissure eruption

Flood basalts: Columbia Plateau, Washington

Thought questions for this chapter

Why are eruptions of stratovolcanoes generally more explosive than those of shield volcanoes?

While on a field trip, you come across a volcanic formation that resembles a field of sandbags. The individual ellipsoid forms have a smooth, glassy surface texture. What type of lava is this, and what information does this give you about its history?

3. Interactions of Volcanoes with Other Geosystems ● Volcanism and the hydrosphere ● fumaroles and geysers ● Volcanism and the atmosphere ● aerosols and ash

Fumarole: Merapi volcano, Indonesia

Old Faithful geyser: Yellowstone National Park

4. Global Pattern of Volcanism

4. Global Pattern of Volcanism ● Basalt-producing spreading centers ● mantle source for lava (decompression melting) ● axial volcanoes of mid-ocean ridge

4. Global Pattern of Volcanism

4. Global Pattern of Volcanism ● Volcanism in subduction zones ● chains of volcanoes ● island arcs ● formation of new continental crust

4. Global Pattern of Volcanism ● Intraplate volcanism: the mantle plume hypothesis ● hot spots and mantle plumes ● sea mounts and island chains ● large igneous provinces

4. Global Pattern of Volcanism

4. Global Pattern of Volcanism: Hawaiian Island Chain / Emperor Seamounts

4. Global Pattern of Volcanism: Yellowstone Volcanic Tracks

4. Global Pattern of Volcanism: Large Igneous Provinces

Thought questions for this chapter

Why are the volcanoes on the northwest side of the Hawaiian Islands dormant whereas those on the southeast side are more active?

5. Volcanism and Human Affairs ● Volcanic hazards ● lahars ● flank collapse ● caldera collapse ● eruption clouds

5. Volcanism and Human Affairs ● Mantle-plume hypothesis ● predicting eruptions ● controlling eruptions

5. Volcanism and Human Affairs ● Natural resources ● volcanic soils ● industrial materials ● ore formation ● heat energy

5. Volcanism and Human Affairs

5. Volcanism and Human Affairs: Potentially Hazardous Volcanoes

5. Volcanism and Human Affairs: Geothermal Energy

Thought questions for this chapter

What might be the effects on civilization of a Yellowstone type caldera eruption, such as the one described at the beginning of this chapter?

How do interactions between volcanic geosystems and the climate system increase volcanic hazards?

Key terms and concepts

Andesitic lava Ash-flow deposit Basaltic lava Caldera Crater Diatreme Fissure eruption Flood basalt Geothermal energy Hot spot Hydrothermal activity Lahar Large igneous province Mantle plume Pyroclastic flow

Key terms and concepts

Rhyolitic lava Shield volcano Stratovolcano Tuff Volcanic geosystem Volcano