The name "Volcano" is originally named after "Vulcano", an Italian Island north of Sicily. Volcano is a cone which is formed above and around a vent by accumulations of erupted volcanic materials such as ash, pumice, lava flows and other volcanic rocks. A volcano constitutes a vent, crater and a cone. The vent of the volcano is an opening at the earths surface. The pipe is a passage way in the volcano in which the magma rises through to the surface during an eruption.
            The crater is a bowl shaped depression at the top of the volcano where volcanic materials like ash, lava, and other materials are released. Solidified lava, ashes, and cinder form the cone. Layers of lava, alternate with layers of ash to build the steep sided cone higher and higher. Since volcanoes erupt different from each other, depending on the kind of rising magma as well as other factors. However, most of the volcanic eruptions take place unseen on the ocean floor. Therefor they are called submarine eruptions.
            The sudden violence of volcanic eruptions causes catastrophe and devastation. Various notorious eruptions of volcanoes in the past such as Mount Pelee, Tambora, Krakatu and Pinatubo have demonstrated the devastating impact of volcanic activity on nearby landscapes and communities. Volcanoes are not randomly distributed over the Earth's surface. Most are concentrated on the edges of continents, along island chains, or beneath the sea forming long mountain ranges. More than half of the world's active volcanoes above sea level encircle the Pacific Ocean to form the circum-Pacific "Ring of Fire." In the past 25 years, scientists have developed a theory called plate tectonics, that explains the locations of volcanoes and their relationship to other large scale geologic features.

Mount Shasta
Shasta, California is the second highest mountain in the Cascade Range. The volcano is composed of four overlapping andesite eruptive centers all visible in the photograph. The oldest center in the Sargents Ridge cone, located on the strongly eroded lower slopes of Shasta, was active about 450,000 years ago.
Misery Hill, on the northwest flank of Shastam was active around 9,200 years ago. The Hotlum cone is the youngest eruptive center and forms Shasta's summit and the north and the northeast flanks. Hotlum cone was active only a few centuries ago.
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Maui and Kahoolawe
The island of Maui is made of two volcanoes. A central caldera has been identified roughly in the area of the present day Iao Valley. Alkalic basalt's capped the volcano about 1.2 million years ago. Kahoolawe is made of tholeiitic and alkalic basalt of the shield and capping stages. A rock from the capping stage has been dated at about 1 million years old.  During the rejuvenated  stage a small number of eruptions occurred near the Kanapou Bay. The age of the rocks are unknown.
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                                   Volcano Hazards
    A volcanic hazard refers to the probability that a given area will be affected by a potentially destructive volcanic process. A volcanic risk is a loss in the hazardous area. Any area near an active volcano is potentially hazardous. Some areas have higher probabilities of being affected by a destructive volcanic process than others. a home built near the summit of a volcano may have the same level risk as one built in a valley 60 km from the volcano.
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                        Causes of Eruptions.
    Deep in the Earth it is so hot that some rocks slowly mely and become a thick flowing substance called magma. Because it is lighter than the solid rock around it, magma rises and collects in magma chambers. Eventually some of the magma pushes through vents and fissures in the Earths surface. Magma that has erupted out of the volcano is called lava.  How explosive an eruption is depends on how runny or sticky the magma is. If magma is thin runny, gases can escape easily from it. Lava flows rarely kill people because they move slowly enough for people to get out of the way.
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                 Signs that an eruption is likely.
Most volcanoes provided various types of warnings before eruptions can occur. Although an explosive eruption could occur without warning, some premonitory events more likely will precede the next eruption.  People living near volcanoes may detect premonitory events before an eruption. Both the frequency of occurrences and intensity of felt earthquakes commonly increase before eruptions begin.
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