1. Section 9.2
Volcanic Eruptions

2. “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

3. 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 , which Munch captured in his painting.

4. What FACTORS determine if a volcano erupts violently or quietly?

5. Quiet eruptions Hawaii & Iceland
Pahoa Lava Flow

6. Explosive, violent eruption
Destructive landslide associated with 1980 Mt. St. Helen's eruption
Krakatoa eruption 2007

7. Before the 1980 eruption After the VIOLENT eruption
The summit and side has been blown away.

8. Bell-work Pyroclastics consist of …… Cinders Lapilli Glass
Ash
Cinders
Lapilli
Glass
Pumice/Obsidian
Bombs
Blocks
Tuff (welded ash)

9. Affiliated with Violent Explosions
Lahar: is a type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris, and water. The material flows down from a volcano, typically along a river valley. (Volcano peaks often have ice and snow that instantly melt when met with the heat of an erupting volcano.)
PYROCLASTIC FLOW: a dense, destructive mass of very hot ash, lava fragments, and gases ejected explosively from a volcano and typically flowing downslope at great speed.

10. Felsic magma Mafec* magma
Factors that affect volcanic eruptions:
Pg 121
Felsic magma Mafec* magma
Feldspar, silica magnesium and iron
Expolsivity depends on the amount of silica and gas in the magma.

11. So thick it acts like a “plug” to the volcano…
FELSIC magma
Light colored minerals:
Quartz, orthoclase Feldspar
More than 60% silica
Lower melting point= colder temperatures (“thick”)
HIGH viscosity
MAFIC magma
Dark colored minerals:
Magnesium and iron Fe
Olivine, pyroxene,
Hornblende, augite, biotite
Less than 50% silica
Higher melting point= hotter temperatures (“thin”)
LOW viscosity
So thick it acts like a “plug” to the volcano…
“Thin” enough that it allows the magma to move more freely…

12. Volatiles
refers to the volatile components of magma [mostly water vapor and carbon dioxide] that affect the appearance and explosivity of volcanoes.
Volatiles in a magma with a high viscosity, generally felsic with a higher silica (SiO2) content, tend to produce eruptions that are explosive.
Volatiles in a magma with a low viscosity, generally mafic with a lower silica content, tend to vent and can give rise to a lava fountain.

13. Volatiles Continued: the effect of trapped gases
How explosive a volcano will be is dependent on the gases present as well
How much gas is present
If a lot of gas is present the volcano is more likely to be more explosive
How easily the gas can escape
If the gases cannot escape easily, the volcano is more likely to be more explosive

14. What happens to bring magma to the surface?
How does the type of magma affect the surrounding pressure? (remember gas is a volatile that affects the reactivity of magma)
Volcanic eruptions and what causes them
Build up of pressure occurs more frequently with thicker magma (felsic.)….. EXPLOSIVE ERUPTION

15. Volcanic Explosivity Index
How to measure a volcanic eruption
There is the Fajita scale for tornadoes, the Safiir-Simpson scale for hurricanes, Richter scale for earthquakes, and the VEI scale for volcanoes

16. 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)

17. Lava Vocabulary Quiz 9.2 pyroclastic
Hot, erupted glass, ash, and rock fragments. ________________
All lava flows are this type of rock. _____________________
3. A basaltic lava that results in smooth, ropelike surfaces: ____________
Magma has a high viscosity if it contains over 60% of ________
If the magma has a high gas content, the eruptions tend to be ________
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
igneous
pahoehoe
silica
explosive
felsic