1. Quiz
The most important factor affecting the size of crystals in an igneous rocks is the:
A. Water pressure around the magma
B. Rate of cooling
C. Size of magma
D. Mineral composition of the magma

2. Quiz
Of the more than 4000 minerals that exist, only ____ of them compose over 95% of all igneous rocks.
A. 3
B. 7
C. 11
D. 16

3. Quiz The two igneous rock types that make up the oceanic crust are:
A. basalt and gabbro
B. granite and rhyolite
C. granite and gabbro
D. andesite and granite

4. Quiz
According to Bowen’s reaction series, which ferromagnesian mineral will crystallize first in a cooling basaltic magma?
A. pyroxene
B. olivine
C. quartz
D. calcium-rich plagioclase

5. Quiz
The basaltic magma that emerges from the mid-ocean ridge is produced by the partial melting of the:
A. lithosphere
B. asthenosphere
C. outer core
D. continental crust

6. Volcanism What is a volcano?
Where do volcanoes occur and how do they erupt?
Materials produced by volcanoes and kinds of volcanic structures
Forecasting volcanic eruptions
Effects of volcanoes on global climate

7. Volcanoes on line volcanoes.usgs.gov
Volcanic hazards in the United States
53 active volcanoes (3rd most volcanically active nation)

8. Anatomy and Setting of a Volcano
Volcano: place where magma, gas, ashes erupt
Vent: cylindrical-shaped outlet for magma
Lava: magma that reached the surface
Crater: bowl-shaped depression

9. Anatomy and Setting of a Volcano
Caldera: larger than crater, formed by collapse
Feeders: network of vents

13. Geometry of volcano and style of eruption
What factor(s) control the slope of a volcano?
Why are some eruptions quiet while others are explosive and extremely destructive?
Is there a correlation between slope of a volcano and its eruptive style?

14. Materials of eruptions
Magma viscosity
depends on silica content, temperature, gases, ev. water depth and reactions with country rocks (e.g., limestone)
Lavas
fine-grained textures with microscopic crystals, glass, bubble cavities; porphyritic texture (basalts, andesites, obsidian)
basaltic and silicic lava flows

15. Materials of eruptions
Pyroclastic material
ash, cinders, lapilli, blocks, bombs
air fall (tephra) or surge deposits (nuée ardente - ignimbrite)
mudflows (lahars)
Volcanic gases
carbon dioxide, water vapor, sulfur dioxide, hydrogen sulfide

18. Volcanic structures and eruptive styles
High-silica eruptions
explosive eruptions
abundant pyroclastic debris
steep cone
Basaltic volcanoes
quiet eruptions
broad, gently sloping cones

19. Volcanic structures and eruptive styles
2/3 of all volcanoes on the Ring of Fire (Pacific subduction zones)
Divergent (basalt) and convergent (andesite, rhyolite) margins
Fissure eruptions and lava plateaus
flood basalts: Columbia Plateau and Deccan Traps
Mount Saint-Helens

20. Forecasting eruptions
Procedures for predictions
Study the geologic setting: field study and radiometric dating
Establish a monitoring system (earthquakes, tiltmeters, gas composition and quantity, heat, groundwater temperature and composition)

21. Vesuvius
Pompeii 79AD
Risk assessment for Vesuvius: Vulcan.fis.uniroma3.it/vesuvio/vesuvius_risk.html

22. Effects of volcanism Volcanism and climate
Atmosphere and climate (dust particles and acid droplets, CO2 and other gases)
Eruption of Mount Pinatubo in 1991
Carbon dioxide and the greenhouse effect
Volcanism can cause both warming and cooling
Positive aspects of volcanism

26. Summary Volcano, vent, caldera, lava, feeders
Tectonic settings of volcanoes
Magma viscosity and eruptive styles
Names of volcanic rocks and composition of lava
Forecasting eruptions
Volcanism and climate