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Volcanism Gulp! Tectonic Settings of Igneous Activity Figure 5.11 The World’s Active Volcanoes Fig. 5.28 Volcanism Associated with Plate Tectonics Fig. 6.19 Material ejected from volcanoes Lava: Magma that has flowed on the surface of the Earth.

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Volcanism l.jpg

Volcanism

Gulp!




Volcanism associated with plate tectonics l.jpg
Volcanism Associated with Plate Tectonics

Fig. 6.19


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Material ejectedfrom volcanoes

  • Lava: Magma that has flowed on the surface of the Earth.

  • Tephra: Fragments that solidified in the air during eruption.



Looking at lava7 l.jpg

Viscosity: Measure of a fluid’s ability to flow.

Higher viscosity = slower flow. (Ketchup has higher viscosity than water.)

Looking at lava ….


Looking at lava8 l.jpg
Looking at lava ….

  • What controls lava viscosity?

    • Temperature: Higher temperature = less viscous.

    • SiO2 content: Higher SiO2 = more viscous.


Two main types of lava l.jpg
Two main types of lava

  • Mafic or basaltic:

    • Lower viscosity

    • Faster lava flows

    • Calmer eruptions

  • Felsic or rhyolitic:

    • Higher viscosity

    • Slower lava flows

    • More violent eruptions


Basaltic lava l.jpg
Basaltic lava

  • Erupts at 1000° to 1200°C

  • Can flow as fast as 100 km/hr (but usually a few km/hour)

  • Can travel as much as 50 km from volcano

  • Flood basalts: Very fluid basaltic flows that spread out in sheets over the landscape. Layered.

Columbia River flood basalts in Washington and Oregon.

Figure 6.2


Basaltic lava11 l.jpg
Basaltic lava

  • Basaltic lava flowing downhill forms pahoehoe or aa.

  • Pahoehoe: (Hawaiian “ropy”). Thin sheet of lava cools on the surface. Skin is twisted and dragged downhill to form “ropes.”

  • Aa: (Hawaiian “ouch”). Lost gas, is more viscous than pahoehoe. Cools to form thick skin. Skin breaks into jagged blocks.

Figure 6.3


Basaltic lava12 l.jpg

Pillow lava: Pillow-like blocks of basalt. ~1 m wide. Formed underwater. Blob of basalt extruded underwater (like toothpaste), skin cools quickly (“quenches”) to form glassy rind.

Basaltic lava


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Fissure eruptions

Central eruptions

Shield volcanoes

Domes

Cones

Stratovolcanoes (composite)

Eruptive stylesand landforms


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Not all lava flows have volcanoes.

When low-viscosity lava erupts from cracks in the Earth tens of kilometers long.

Make flood basalt provinces.

Fissure eruptions

Laki fissure (Iceland) erupted in 1783 extruding the largest lava flow in human history (Fig. 6.13).





Shield volcanoes l.jpg

Low-viscosity lava flows (low silica, mafic).

Successive lava flows.

Gently sloping flanks (between 2 and 10 degrees)

Tend to be very large (many 10s of km in circumference)

Shield volcanoes

Fig. 6.9


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Mauna Loa -- world’s largest structure -- 10 km above ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows


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? ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows

Is Mauna Loa about to erupt again?


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Forms above a volcanic vent ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows

Viscous lava — usually silica-rich (or cooler magma)

Associated with violent eruptions

Volcanic domes

Fig. 6.9


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Mt. St. Helens ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows

Lava

Dome

Lyn Topinka/USGS


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Cinder Cone ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows

  • Formed of pyroclastics only

  • Steep sides — ~30 degrees

  • Relatively small

  • Short duration of activity

Fig. 6.9


Cerro negro cinder cone near managua nicaragua in 1968 erupted again in 1995 and 1999 l.jpg
Cerro Negro Cinder Cone, near Managua, Nicaragua ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows in 1968 (erupted again in 1995 and 1999)

Mark Hurd Aerial Surveys


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Pyroclast? ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows

A volcanic rock fragment ejected into the air during an eruption. Loss of gases due to pressure drop results in explosive eruption.

Classified according to size.

Volcanic ash <2 mm in diameter.

Volcanic bombs: Blobs of lava that cool as they fly trough the air. Can be as big as houses.


Pyroclasic eruption at arenal volcano costa rica l.jpg
Pyroclasic Eruption at Arenal Volcano, Costa Rica ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows

Gregory G. Dimijian/Photo Researchers

Fig. 6.5


Volcanic bomb l.jpg
Volcanic Bomb ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows

Fig. 6.5

Science Source/Photo Researchers


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Lithification of pyroclasts ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows

Volcanic tuffs: Rocks created from smaller fragments.

Volcanic breccias: Rocks formed from larger fragments.


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Volcanic Breccia ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows

Fig. 6.7

Fig. 5.8

Doug Sokell/Visuals Unlimited


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Welded Tuff: California ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows

1 foot

Gerals and Buff Corsi/Visuals Unlimited


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Ash-flow Sheets Draping Topography, Japan ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows

S. Aramaki


Composite volcano l.jpg

Alternating pyroclastic layers and lava flows ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows

Slopes intermediate in steepness

Intermittent eruptions over long time span

Mostly andesite

Circum-Pacific Belt (“Ring of Fire”), Mediterranean Belt

Composite volcano

Fig. 6.9


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Mt Fujiyama, Japan ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows

Fig. 5.15

Raga/The Stock Market


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Caldera ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows


Crater lake oregon l.jpg
Crater Lake, Oregon ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows


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Phreatic Eruption ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows

An extremely explosive eruption that occurs when hot lava encounters cool seawater. Huge quantities of steam are released.

Phreatic eruption on a Pacific island south of Tokyo.

Fig. 6.11


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Hot Spots ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows

Fig. 6.19


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Hot Spots ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows

What is a hot spot?

A hot spot is the surface expression of a mantle plume.

What is a mantle plume?

A narrow, cylindrical jet of hot material, rising from deep within the Earth (perhaps the core-mantle boundary) that gives rise to surface volcanism.


Hot spots39 l.jpg
Hot Spots ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows

Fig. 6.22


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Hot Spots ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows

Fig. 6.20


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Hot Spots ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows

Fig. 6.20


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Hot Spots ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows

Fig. 6.20


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Large Igneous Provinces ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows

Fig. 6.21


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Lava Flows: ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flowse.g. Hawaii, 1998

Gas: e.g. Lake Nyos (Cameroon), 1984

1700 people killed

Ash fall: e.g. Mt. Pinatubo, 1991

Pyroclastic flows: e.g. Mt. Pelee, 1902

28,000 killed

Lahars (mudflows): e.g. Nevado del Ruiz, 1985

23,000 killed

Tsunami: e.g. Krakatoa, 1883

36,417 killed

Types of Volcanic Hazards


May 1990 eruption of kilauea hawaii l.jpg
May 1990 Eruption of Kilauea, Hawaii ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows


San juan mexico buried by paricutin lava flows l.jpg
San Juan, Mexico. ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flowsBuried by Paricutin Lava Flows.


U s active volcanoes l.jpg
U.S. Active Volcanoes ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows


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Before May, 1980 ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows

Emil Muench/Photo Researchers


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After May, 1980 ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows

David Weintraub/Photo Researchers


Japan l.jpg
Japan ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows


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Mt. Pinatubo ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows


Mudflow or lahar l.jpg
Mudflow or Lahar ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows

  • A mixture of water and pyroclastic material and sand, gravel, and boulders, in a concrete-like slurry capable of moving up to 100 km/hour

  • Flow is supported by collisions between clasts


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Mudflow ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows


23 000 killed in 1985 by volcanic mudflows nevada del ruiz l.jpg
23,000 killed in 1985 by volcanic mudflows, Nevada del Ruiz ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows


Columbia l.jpg
Columbia ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows

The only remaining buildings in Armero, Colombia, 72 km dowstream from Nevado del Ruiz volcano, destroyed and partially buried by lahars on November 13, 1985. Lahars reached Armero about 2.5 hours after an explosive eruption sent hot pyroclastic flows across the volcano's broad ice- and snow-covered summit area. Although flow depths in Armero ranged only from 2 to 5 m, three quarters of its 28,700 inhabitants perished.


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Mt. Rainier ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows


Escaping a pyroclastic flow at mount unzen japan 1991 fig 6 8 l.jpg
Escaping a Pyroclastic Flow at Mount Unzen, Japan, 1991 ocean base -- base diameter of 120 km -- took 1 million years to grow from successive lava flows(Fig. 6.8)

Pyroclasticflow (nueé ardente)

  • Mixture of hot gases, ash, and rocks forming a super-heated and dense current capable of moving 150 km/hr.

  • Buoyancy due to heated gas, density due to ash- turbulence keeps particles suspended in flow


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Pyroclastic flows erupted by Mount Pinatubo on June 15, 1991, buried the Marella River valley (SW of Pinatubo) with pumice, ash, and other volcanic rocks to depths of between 50 and 200 m. This eruption was one of the largest in the 20th century, depositing about 5.5 km3 of rock debris over nearly 400 km2.


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