Geography 111 - Principles of Geology
Review questions for Sept. 17-24: Magma, igneous rocks, and volcanic activity
NOTE: These questions are presented in the same order as the topics in chapter 3 of the textbook, as an
aid to studying assigned readings; however we will cover these topics in a somewhat different order in
class. We will also have a special unit in class on the 1991 eruption of Mt. Pinatubo, which was the largest eruption in the world in the last 80 years.
What are the physical and chemical properties of the principal kinds of magma? How are silica
content, temperature, gas content, and viscosity of a magma related to the type of volcanic rock (e.g.
basalt, andesite, dacite, rhyolite) that forms if it erupts at the earth's surface?
How are all of the above related to the type of eruption that occurs and the textural characteristics of
the volcanic deposits left behind by the eruption? How are pyroclastic deposits and tephra different
from the types of deposits that form from basaltic lava? What are vesicles; lava domes; plateau
basalts, and pillow basalts?
What are the major types of volcanoes and how are they related to the physical and chemical
characteristics of the magma, the types of eruptions, and the characteristics of the deposits left behind
by those eruptions?
What is the sequence of events leading to formation of calderas such as those at Crater Lake or the
Taal volcano?
What are the major types of geologic hazards and environmental impacts associated with volcanic
eruptions, and which kinds of volcanoes are typically associated with which kinds of hazards?
What are the principal differences between intrusive (plutonic) and extrusive (volcanic) igneous rock?
How are the different textural varieties, e.g. ranging from glassy to fine-grained to coarse-grained to
mixed texture (porphyritic) related to the way the rock forms? How are tuffs different from other types
of igneous rocks?
What dominant assemblages of silicate minerals are associated with the major varieties of intrusive
igneous rock? Which extrusive rocks are compositionally equivalent to each of these varieties?
What are plutons and what are the similarities and differences between dikes, sills, laccoliths, volcanic
pipes or necks, batholiths, and stocks?
How does the concept of magmatic differentiation by either partial melting or fractional
crystallization help to explain the origin and evolution of different types of magma (e.g. basaltic,
andesitic, and rhyolitic)? What is the role of water in partial melting? What does all of this have to do
with plate tectonics?
How is Bowen's reaction series related to the magmatic differentiation processes described above and
how is it related to the assemblages of minerals found in different kinds of igneous rocks?