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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
Page 121
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.