As the 1991 eruption of Mount Pinatubo shows, volcanoes can
go hundreds of years between eruptions. Before Pinatubo’s eruption,
scientists noticed warning signs that included the occurrence of many
small earthquakes followed by explosions of steam near the volcano’s
top. Researchers brought in equipment to monitor the volcano’s
activity. Although they could not stop the eruption, they
were able to tell when people should leave.
Scientists monitor volcanoes around the world for
signs of eruptions. Indications that magma is moving
underneath a volcano include earthquake activity and
changes in the tilt of the ground. Scientists also monitor
the temperatures at openings, springs, and lakes on
volcanoes, as well as the amounts and types of gases
given off by the volcanoes. Rising temperatures and
changes in volcanic gases can indicate that fresh magma
has moved into a shallow magma chamber.
Scientists study the ages and types of volcanic rocks
around a volcano to understand the volcano’s history,
including how much time has passed between eruptions
and how violent the eruptions have been. This information gives clues about possible future eruptions.
The robot Dante II is about to enter the
crater of Mt. Spurr, Alaska, where it will
collect video data as well as water and
gas samples.
Even with close monitoring, most property damage
from volcanic eruptions cannot be prevented. But warning
people to move away from a volcano that is about to
erupt can save lives. Many of the active volcanoes that are closely
monitored are located near major cities. Among these are Mount
Rainier (ruh-NEER), which is near Seattle, Washington, and Mount
Vesuvius (vih-SOO-vee-uhs), which is near Naples (NAY-puhlz), Italy.
check your reading
What is the purpose of monitoring volcanoes?
KEY CONCEPTS
CRITICAL THINKING
1. Where are most volcanoes
located, and why are they
located there?
4. Compare and Contrast
How do the three main types
of volcanoes differ?
2. How does the type of material
that erupts from a volcano
determine the shape of the
volcano?
5. Infer Volcanic ash can be
deposited in areas many
kilometers away from the
volcano that produced it. What
are two ways in which the ash
can reach these areas?
3. What conditions do scientists
examine when they monitor
volcanoes?
CHALLENGE
6. Analyze Draw diagrams
showing how a composite
volcano might change in shape
by getting larger or smaller
with repeated eruptions.
Chapter 8: Mountains and Volcanoes 269