A volcano is a mountain that opens downward to a reservoir of molten rock 

below the surface of the earth. 

Unlike most mountains, which are pushed up from below, volcanoes are vents 

through which molten rock escapes to the earth’s surface. 

When pressure from gases within the molten rock becomes too great, an eruption occurs.

Eruptions can be quiet or explosive.

There may be lava flows, flattened landscapes, poisonous gases, and flying rock and ash 

that can sometimes travel hundreds of miles downwind.

Because of their intense heat, lava flows are great fire hazards.

Lava flows destroy everything in their path, but most move slowly enough 

that people can move out of the way.

Fresh volcanic ash, made of pulverized rock, can be abrasive, acidic, gritty, gassy and odorous. 

While not immediately dangerous to most adults, the acidic gas and ash can cause lung damage 

to small infants, to older adults and to those suffering from severe respiratory illnesses.

Volcanic ash also can damage machinery, including engines and electrical equipment. 

Ash accumulations mixed with water become heavy and can collapse roofs. 

Volcanic ash can affect people hundreds of miles away from the cone of a volcano.

Sideways directed volcanic explosions, known as "lateral blasts," can shoot large pieces 

of rock at very high speeds for several miles. 

These explosions can kill by impact, burial or heat. 

They have been known to knock down entire forests.

Volcanic eruptions can be accompanied by other natural hazards, 

including earthquakes, mudflows and flash floods, rock falls and landslides, 

acid rain, fire, and (under special conditions) tsunamis.

Active volcanoes in the U.S. are found mainly in Hawaii, Alaska and the Pacific Northwest.

There are 18 states which have volcanoes:

Alaska, Arizona, California, Colorado, Hawaii, Idaho, Mississippi, Missouri, Nevada, 

New Hampshire, New Mexico, Oregon, South Dakota, Texas, Utah, Virginia, Washington, and Wyoming

There are 5 states which have what are considered active volcanoes:

Alaska, California, Hawaii, Oregon and Washington.

The danger area around a volcano covers approximately a 20-mile radius 

however, some danger may exist 100 miles or more from a volcano.