W
HY DO VOLCANOES
LIKE MOUNT
ST. HELENS ERUPT
explosively, whereas others like the
Hawaiian volcano Kilauea are
relatively quiet? Why do volcanoes
occur in chains like the Aleutian
Islands or the Cascade Range?
Why do some volcanoes form on the
ocean floor, while others occur on the
continents?
This chapter will deal with these and
similar questions as we explore the nature
and movement of magma and lava.
F O C U S O N C O N C E P T S
To assist you in learning
the important concepts in this
chapter, focus on the following
questions:
What primary factors determine
the nature of volcanic eruptions?
How do these factors affect a
magma’s viscosity?
What materials are associated
with a volcanic eruption?
What are the eruptive patterns
and basic characteristics of the
three types of volcanoes
generally recognized by
volcanologists?
What destructive forces are
associated with composite
volcanoes?
How do calderas form?
What is the source of magma for
flood basalts?
What is the relation between
volcanic activity and plate
tectonics?
What changes in a volcanic
landscape can be monitored to
detect the movement of
magma?
A recent eruption of Italy’s Mount
Etna. (Photo by Marco Fulle)