Volcanoes 1-3

Volcanoes 1-3

The nonfiction selection Volcanoes discusses volcanoes in myth and legend, and then explains how volcanoes form and what causes them to erupt, or pour out lava and ash.

The earth is made up of layers of rock. The top layers are called the earth's crust. Deep below the crust, it is hot enough to melt some of the rock, forming magma. Volcanoes form where there are cracks or holes in the crust. Magma pushes up through the crack, causing an eruption. The hot magma that pours out is called lava. When the lava cools, it hardens into rock. Thick lava that moves slowly hardens into sharp rocks. Thin lava that moves quickly forms smooth rocks.

The earth's crust is broken into huge pieces called plates. Most Volcanoes erupt in places where two plates come together, especially along the rim of the Pacific Ocean. There are underwater volcanoes, too. When they erupt, they can grow high enough to stick up out of the ocean and form islands, like Surtsey in Iceland and Mauna Loa in Hawaii.

There are four different types of volcanoes. Shield volcanoes, like Mauna Loa, have gentle slopes. Cinder cone volcanoes look like upside-down ice cream cones. Most volcanoes are composite or strato-volcanoes. They are formed when lava covers layers of cinder and ash. The last kind of volcano is a dome volcano. Its thick lava creates a steep, dome-like shape.

When volcanoes do not erupt anymore, they are considered extinct. An example is Crater Lake in Oregon.

The explosion of Mount St. Helens in 1980 shows how destructive an eruption can be. But volcanic eruptions can also create new mountains, islands, and soil.