Volcanos are openings in the earth's crust through which molten lava, ash, and gases are ejected. They have caused some of the worst disasters in history, including wiping out entire cities and killing thousands of people. They impressed the Romans so much that their god of fire was represented by a volcano. In fact, that's where the word comes from. It comes from Vulcan, the Roman fire god. They believed that Vucan lived on an island of the Italian coast. The island was volcanic. They called the island Vulcano.
Scientists have divided volcanic eruptions in to four basic groups based on the violence of the eruption and the type of material that erupts. The four groups are Hawaiian, Strombolian, Vulcanian, and Peleean. Hawaiian eruptions are named after the volcanoes in Hawaii and are the least violent type. They produce highly fluid lava that flows quietly from several vents. This gradually builds up a shield volcano.

Strombolian eruptions are named after Stromboli. These result from the constant release of gas from the magma. As the gas escapes, it produces tephra that piles up, turning into a cinder cone. Volcanic eruptions get their name from the Roman island Vulcano. Strombolian eruptions happen when sticky magma plugs the central vent. This makes the magmatic gas build up pressure until it blasts. The magma is turned into volcanic dust and bombs. The most violent kind of eruptions are the Peleean. Their name comes from the eruption of Mount Pelee in 1902 on Martinique, which killed almost 38,000 people. A Peleean eruption occurs when the magmatic gas build up tremendous pressure. This causes violent explosions with glowing clouds of hot ash and dust. Most of the volcano gets torn apart too.

It is very hard to predict when a volcanic eruption will occur and most cannot be predicted. When volcanoes erupt, little to nothing can be done to save property, but many lives can be saved if the area if evacuated soon enough.It is a constant priority for scientists to figure out how to predict them, and they have already made a little progress. Scientists use several devices to figure out when a volcano will erupt. One such instrument is called a tilt-meter, they use it to measure the expansion of a volcano. Thermometers are often used to check the temperature in the surrounding area and gas detectors are used to measure the amount of gas. Though these instruments aren't perfect, they do help.

Volcanoes also have many benefits. Many volcanic materials have important industrial and chemical uses. Lava rocks can be used in roads, while pumice is used for grinding and polishing metals and other materials. Volcanic ash improves soil fertility and the underground steams volcanoes produce can be used as a source of energy. Besides these everyday uses, scientists can use volcanoes as "windows" to the inside of the earth. By studying them and the materials they erupt, scientists can gain a better understanding of the earth.

The first picture is of an erupting volcano, courtesy of http://georoc.mpch-mainz.gwdg.de/volcano.gif The second picture is of an active volcano, courtesy of http://www.solis-media.co.uk/relocated/3dimagery/images/largeimages/volcano.jpg