volcano is a mountain that opens downward to a pool of molten rock below the surface of the earth. When pressure builds up, eruptions occur. Gases and rock shoot up through the opening and spill over or fill the air with lava fragments. Eruptions can cause lateral blasts, lava flows, hot ash flows, mudslides, avalanches, falling ash and floods. Volcano eruptions have been known to knock down entire forests. An erupting volcano can trigger tsunamis, flashfloods, earthquakes, mudflows and rockfalls.

volcanoes in the U.S. are found mainly in Hawaii, Alaska, California, Oregon and Washington. The greatest chance of eruptions near areas where many people live is in Hawaii and Alaska. The danger area around a volcano covers about a 20-mile radius. In May 18, 1980, Mount St. Helens erupted in Washington state. It killed 58 people and caused more than $1 billion in property damage.

volcanic ash, made of pulverized rock, can be harsh, acidic, gritty, glassy and smelly. The ash can cause damage to the lungs of older people, babies and people with respiratory problems.