Formation of Crater Lake
Crater Lake fills the caldera of a composite volcano.
A huge eruption removed much of the
magma from the magma chamber.
The volcano collapsed, creating a
caldera 8 kilometers in diameter and
1.6 kilometers deep.
New eruptions built a small cone in
the caldera. The caldera filled with
water from rain and snow.
Both shield volcanoes and composite volcanoes can form features
called calderas (kal-DAIR-uhz). A caldera is a huge crater formed by
the collapse of a volcano when magma rapidly erupts from underneath
it. The crater at the top of Mauna Loa in Hawaii is a caldera. Crater
Lake in Oregon fills a caldera formed by a composite volcano about
7700 years ago. A violent eruption emptied much of its magma chamber, and the top of the volcano collapsed into it. The caldera now
holds the deepest lake in the United States.
Scientists monitor volcanoes.
CONTENT FRAME
Make a content frame for
types of data used to
predict eruptions. Include
categories for current
activity and history.
268 Unit 2: The Changing Earth
Before Mount Pinatubo (PIHN-uh-TOO-boh) in the Philippines erupted
in 1991, most people living in the area did not realize that it was a
composite volcano. It had not erupted in about 500 years, and erosion
had changed its shape. Fortunately, scientists in the Philippines knew
that the volcano was becoming active months before it exploded. They
were able to warn the government and ask people to leave the area.
Their efforts probably saved tens of thousands of lives.