What is a volcano? A volcano is a crack or hole in the crust of the Earth through which molten (melted) rock rises to the surface to form a mountain. The surface of the Earth is divided into "plates".
 

    In this project, we are looking at volcanoes in the United States. All of the volcanoes in the United States are found in the western states, and in Alaska and Hawaii.
 
 
 

Alaska
Arizona
California
Colorado
Hawaii
Idaho
New Mexico
Nevada
Oregon
Utah
Washington
Wyoming
 
 
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    If we could look down underneath a volcano, we would see rock so hot that it is melted. This melted rock is called magma when it is under the surface of the Earth. There is a lot of pressure on the magma. If the magma is squeezed all the way to the surface, we say the volcano is erupting. The magma is now called lava. The lava is not under any pressure, so it can flow. Some kinds of lava are almost as runny as water, and other kinds are very thick.
 
    There are several types of volcanoes. Shield volcanoes have gentle slopes like a shield, because they are made of many layers of a kind of volcanic rock that flows easily when melted. This kind of rock is called basalt. When it flows out of a vent in the earth's surface it forms thin layers sloping away from the crater. Some shield volcanoes get to be very large. The volcanoes that make up the Hawaiian Islands are shield volcanoes.

Kahoolawe, Hawaii           Cinder cones are made of bits of a kind of volcanic rock called andesite. Sometimes there are bits of basalt too. These bits of rock are called cinders. They may be tiny, like ash, or larger like gravel. They get blown out of the vent and harden in the air. When they land, they pile up around the crater to form a steep cone. Cinder cones are often smaller than shield volcanoes, and they wear away easily.   Amboy Crater, California         Stratovolcanoes (also known as composites) are made of layers of cinders between layers of lava. The layers of cinders makes the sides steep, and the layers of hardened lava keep them from wearing away fast. Many famous volcanoes like Mt. Saint Helens and Mt. Rainier in Washington are stratovolcanoes.   Mt. Rainier, Washington  
 
 

    Caldera volcanoes are very large stratovolcanoes that collapsed after an eruption. Crater Lake in Oregon is an example of a caldera. About 7000 years ago it was a volcano we now call Mt. Mazama. It erupted many times, blowing gas and magma into the air and spilling lava over the edge of the crater. When Mt. Mazama stopped erupting, it had a large empty space underneath. Eventually the space got so big that the top of the mountain caved in. Three cinder cones later erupted in the center of the crater. Over hundreds of and hundreds of years, the crater filled up with rain, snow, and ice. One of the cinder cones can still be seen above the water. It is called Wizard Island.

  Crater Lake, Oregon           Lava domes (also known as volcanic domes) occur next to craters of stratovolcanoes. They are relatively small and form when very sticky lava erupts slowly from a vent. They can also be very explosive. Mt. Saint Helens in Washington has a lava dome.   Mono Craters, California                 When a volcano erupts, not only does the lava come out, but dust and gas shoot into the sky too. The falling dust is called ash. Earthquakes may also happen before, during, and after eruptions. Some volcanoes erupt very quietly, and others may send tons of steam, ash, and rocks into the air with a large, loud explosion.             When Mount St. Helens erupted on May 18, 1980, it caused millions of dollars in damage to homes, roads, crops, and forests. The ash plume could be seen for hundreds of miles. Even though it caused a lot of damage, within a year there were plants and new trees growing on the mountain. Animals and birds came back quickly, too. Today scientists can go down into the crater and study the lava dome.     Near Mt. Saint Helens...18 years after the eruption                           There are a lot of great places on the Internet to find information about volcanoes.  Here are some we like:

USGS Volcanoes
Volcanoes Online
Volcanoes . Com 
Volcano World
Cascades Volcano Observatory
Volcano Watch
The Volcanic Jump Station
NeMO Cruise 1998 - Education/Public Outreach 
Michigan Tech Volcanoes Page
Yahoo! Search Results
 
 

We hope you have had a great time learning about volcanoes.  Thanks for visiting us!