1. Predicting volcanic eruptions

2. F D C B A

3. Outline • Review of igneous rocks, magmas, and types of volcanoes
• Peaceful vs. explosive eruptions
• Predicting volcanic eruptions
• Airplane flight paths and
risks posed by volcanic ash

4. Texture
Chemical
Composition
Plutonic
Volcanic

5. Plutonic & volcanic equivalents
Felsic
Rhyolite
Granite
Obsidian
Quartz
monzonite
Andesite
Gabbro
Basalt
Mafic
Plutonic
Volcanic

6. 2) Dissolved gases in the magma
What controls whether an eruption
is a peaceful lava flow or
explosive?
SiO2
Viscosity of the magma
SiO2
— Composition (How much SiO2?)
— Temperature
2) Dissolved gases in the magma
Dissolved gases

7. Magmas vs. Eruptions Peaceful… Explosive! Mafic Felsic SiO2
Temperature
( °C)
( °C)
Viscosity

8. Low SiO2 magmas = Low gas content = Shield volcanoes
High-SiO2 magmas = High gas content = Composite volcanoes

9. Explosivity of volcanoes
VEI Description Plume Height Volume How often Example
0 non-explosive m s m3 daily Kilauea
1 gentle m ,000s m3 daily Stromboli
2 explosive km ,000,000s m3 weekly Galeras, 1992
3 severe km ,000,000s m3 yearly Ruiz, 1985
4 cataclysmic km ,000,000s m 's of years Galunggung, 1982
5 paroxysmal km km 's of years St. Helens, 1980
6 colossal km s km 's of years Krakatau, 1883
7 super-colossal 25 km s km 's of years Tambora, 1815
8 mega-colossal 25 km ,000s km ,000's of years Yellowstone, 2 Ma

10. Haleakala, Maui
Shield volcano

11. Peaceful eruption

12. Composite volcanoes — think subduction!

14. Volcanism around the globe

16. The Tectonic Plates

17. Mount St. Helens — Before
Composite volcano

18. Explosive volcanism
Mount St. Helens — May 18, 1980

19. Mount St. Helens — After

20. Predicting eruptions
Before an eruption, magma moves into the area beneath the volcano and collects in a magma chamber; this magma movement causes changes in the volcano that scientists can measure.

21. Predicting eruptions 1. Gas released -
Measure volume and composition
2. Small earthquakes produced Measure with seismometer,
look for harmonic tremors
3. Slight swelling of the volcano slope. Measure with tiltmeter, GPS
4. Hydrologic changes

22. Seismicity at Mount St. Helens in 1980

23. Seismicity at Mt. St. Helens in the last 10 years

24. Seismicity and depths of seismicity Mount St
Seismicity and depths of seismicity Mount St. Helens in the last 10 years

25. Notice how big these earthquakes are...

26. How is seismicity before a volcanic eruption
different from seismicity related to
subduction zones?

27. How is seismicity before a volcanic eruption
different from seismicity related to
subduction zones?
They differ in the…
• Size (magnitude) of the earthquakes
• Location of the hypocenters
• Types of seismic waves generated
• Cause of the quakes

30. Regular, constant shaking related to
Harmonic tremors
Examples from Mt. St. Helens
Regular, constant shaking related to
magma moving
underneath a volcano

31. Harmonic tremors vs. P- and S-waves

32. New lava dome
Mount St. Helens
February 25, 2005

34. Mt. Rainier

35. Mt. Ranier The periodic melting of glacier ice from Mt
Mt. Ranier The periodic melting of glacier ice from Mt. Rainier has generated at least 50 major lahars over the past 10,000 years.
A major mudflow descends down the White River once every 600 years.
More than 300,000 people now live in the area covered by these extensive lahars!

36. Lahar or mud flow — One of the deadliest hazards
that occur with snow melt or rain

37. Mayon volcano, Philippines
Ash —
Most common type of eruption
Pyroclastic flows —
One of the deadliest hazards

38. Mt. Pinatubo — the Philippines — June 1991

46. Clark Air Force base before and after — The Philippines 1991