section 9.2 volcanic eruptions. what factors determine if a volcano erupts violently or quietly?

Section 9.2

Volcanic Eruptions

What FACTORS determine if a volcano erupts violently or quietly?

Quiet eruptions

Hawaii & Iceland

https://www.youtube.com/watch?v=fmCJSS2YAP0

Explosive,violent

eruption

https://www.youtube.com/watch?v=IhU6jml6NY4

Felsic magma Mafec* magma

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Feldspar, silica magnesium and iron

Which has a HIGH viscosity?

honey

water

Resistance to flow

MAFIC magma

• Dark colored minerals:• Magnesium and iron Fe • Olivine, pyroxene,

Hornblende, augite, biotite

• Less than 50% silica

• LOW viscosity

FELSIC magma

•Light colored minerals:•Quartz, orthoclase Feldspar•More than 60% silica

•HIGH viscosity

Geode CD-ROM

Lesson 1. Nature of Volcanic Eruptions

And

Lesson 2. Materials Extruded During

Volcanic Eruptions

Bell-workPyroclastics consist of ……--------

AshCindersLapilliiGlassPumiceBombsBlocksTuff (welded ash)

Bell-work4. What is 1 difference and 1 similarity between a …

Pyroclastic flow and a Lahar

VEI Description Plume Height Volume Classification How often Example

0 non-explosive <100 m 1000s m3 Hawaiian daily Kilauea

1 gentle 100-1000 m 10,000s m3 Haw/Strombolian daily Stromboli

2 explosive 1-5 km 1,000,000s m3 Strom/Vulcanian weekly Galeras, 1992

3 severe 3-15 km 10,000,000s m3 Vulcanian yearly Ruiz, 1985

4 cataclysmic 10-25 km 100,000,000s m3 Vulc/Plinian 10's of years Galunggung, 1982

5 paroxysmal >25 km 1 km3 Plinian 100's of years St. Helens, 1981

6 colossal >25 km 10s km3 Plin/Ultra-Plinian 100's of years Krakatau, 1883

7 super-colossal >25 km 100s km3 Ultra-Plinian 1000's of years Tambora, 1815

8 mega-colossal >25 km 1,000s km3 Ultra-Plinian 10,000's of years Yellowstone, 2 Ma

Volcanic Explosivity IndexHow to measure a volcanic eruption

Paroxysmal

• a sudden outburst of a violent eruption

• an increase of periodic eruptions • An eruption with a (V.E.I.) Volcanic

Explosivity Index of 5 (on a scale of 0-8)

Lava Vocabulary Quiz 9.2 1. Hot, erupted glass, ash, and rock fragments. ________________

2. All lava flows are this type of rock. _____________________

3. A basaltic lava that results in smooth, ropelike surfaces: ____________

4. Magma has a high viscosity because it contains over 70% of ________

5. If the magma has a high gas content, the eruptions tend to be ________

6. Because of their high silica content, this rock is light colored. ________

viscosity lava aa pahoehoe

pillow lava pyroclastic ash silica

cinders igneous metamorphic sedimentary

non-explosive mafic explosive felsic

pyroclastic

igneous

pahoehoe

silica

explosive

felsic

Before the 1980 eruption

After the VIOLENT eruption

The summit and side has been blown away.

A portion of the side of the mountain was “blown

away” leaving the mountain less steep.

Flatter terrain then before.

*Construct the profile activity

“I was walking along a path with two friends – the sun was setting - suddenly the sky turned blood red - I paused, feeling exhausted, and leaned on the fence - there was blood and tongues of fire above the blue-black fjord and the city - my friends walked on, and I stood there trembling with anxiety - and I sensed an infinite scream passing through nature."

Edvard Munch

An agonized figure wails against a blood red Norwegian skyline in Edvard Munch's “The Scream” (1893) in the National Gallery, Oslo, Norway

The 1883 eruption of the volcano Krakatoa in Indonesia put so much ash into the atmosphere, it caused unusually intense sunsets throughout Europe in the winter of 1883-4, which Munch captured in his painting.

Based upon the description…

1. What type of volcano was this?shield, stratovolcano, cinder cone

2. What type of magma erupted? mafic or felsic

3. What type of plate boundary does this volcano lie on? Convergent, divergent, transform

4. What would the eruption be on the V.E.I.