Volcanoes
Objectives- Be able to describe the regions where most volcanoes happen at.
A volcano is a weak spot on the earth’s surface where melted rock comes to the surface. The
melted rock, when it is underground, is called magma. Magma also contains gases and water vapor.
Once magma is on the surface, it is called lava. When volcanoes erupt, new rock is added to the earth’s
surface. Volcanoes are considered to be constructive
(building) forces.
Most volcanoes are found along plate
boundaries. This may include convergent boundaries
and divergent boundaries. One major volcanic belt is
called the Pacific Ring of Fire. It borders the Pacific
Ocean.
Many of the volcanoes along the Ring of Fire
form at convergent plate boundaries. These can
include ocean/continental such as long the northwest
coast of the United States including Mt. St. Helens and Mt. Hood and along the west coast of South
America. Japan, the Philippian Islands, and New Zealand form at convergent ocean/ocean convergent
plate boundaries. These volcanic islands along plate boundaries are called island arc volcanoes.
Other volcanoes form at divergent plate boundaries. In places such as along the Mid Atlantic
Ridge, ocean crust is being pulled apart. Many of the volcanoes along the Mid Atlantic Ridge remain
below the surface of the water. Iceland, one of the most volcanic places on earth, is along the Mid
Atlantic Ridge. Mt. Kilimanjaro in Africa is at a divergent plate boundary where continental crust is being
pulled apart.
Other volcanoes form at Hot Spots, or weak spots in the crust away from plate boundaries
where magma rises to the surface. Two examples of hot spots include Hawaii and Yellowstone.
1. What is a volcano?
2. A mixture of rock forming materials, gases and water from the mantle is called __________________.
3. When magma reaches the surface of the earth, it is called _________________.
4. What is the Ring of Fire?
5. Describe how volcanoes from at divergent plate boundaries. Use knowledge from earlier in this unit
to help with the explanation.
6. T/F Many volcanoes form near converging plate boundaries where oceanic crust returns to the
mantle.
7. How does subduction at converging plate boundaries lead to the formation of volcanoes? Use
knowledge from earlier in this unit to help with the explanation.
8. Volcanoes at plate boundaries where two oceanic plates collide create a string of islands called a(n)
______________________________________.
9. What types of plates collide to form the Andes Mountains of South America?