What is a Volcano?
One of the most difficult problems of standardization has been the varying usage of the word “volcano.” Definitions of “volcano” range from individual vents, measured in meters, through volcanic edifices measured in kilometers or tens of kilometers, to volcanic fields measured in hundreds of kilometers. In a database compilation, the disadvantage of the narrowest definition is not so much the multiplicity of names introduced, as the dismembering of a single volcanic plumbing system’s history into apparently unrelated separate records. The interiors of ancient volcanoes, now eroded and exposed for geologic study, show us that most subsurface magma chambers–the suppliers of lavas to overlying volcanoes–are at least several kilometers in diameter. We also know that many contemporary volcanoes grow by additions from countless flank vents as well as activity at a central crater. Consequently, we have tended to group closely spaced “volcanoes” such as the historical vents of the Canary Isl
Many readers know that the island of Hawai`i is made of five volcanoes—Kilauea, Mauna Loa, Hualalai, Mauna Kea, and Kohala. Those same readers know that such obvious features as the cones that dot Mauna Kea, the Hala`i Hills (on Mauna Loa in Hilo), Kulani Cone (on Mauna Loa), and Kapoho Cone and Mauna Ulu (on Kilauea) are places where eruptions took place in the past. But if that’s the case, then why aren’t they called volcanoes? Isn’t a volcano a place where lava reaches the surface of the earth? Why doesn’t the island have hundreds of volcanoes instead of only five? In one dictionary meaning of the word, a volcano is a vent in the earth’s crust through which rock or lava is ejected. In another, a volcano is a cone-shaped hill or mountain built around a vent. Most volcanologists disagree with both of these dictionary definitions. To a volcanologist, a volcano is a structure containing a vent or cluster of vents fed by magma rising directly from great depth within the earth, generall
A volcano is a vent or chimney which transfers molten rock known as magma from depth to the Earth’s surface. Magma erupting from a volcano is called lava and is the material which builds up the cone surrounding the vent. A volcano is active if it is erupting lava, releasing gas or generates seismic activity. A volcano is dormant if it has not erupted for a long time but could erupt again in the future. Once a volcano has been dormant for more than 10,000 years, it is termed extinct. The explosiveness of a volcanic eruption depends on how easily magma can flow and the amount of gas trapped within the magma. Large amounts of water and carbon dioxide are dissolved in magma causing it to behave in a similar way to gas expanding in fizzy drinks, which forms bubbles and escapes after opening. As magma rises quickly through the crust, gas bubbles form and expand up to 1,000 times their original size. Volcanoes can be different in appearance with some featuring perfect cone shapes while others
Volcanoes The word “volcano” comes from the little island of Vulcano in the Mediterranean Sea off Sicily. Centuries ago, the people living in this area believed that Vulcano was the chimney of the forge of Vulcan — the blacksmith of the Roman gods. They thought that the hot lava fragments and clouds of dust erupting form Vulcano came from Vulcan’s forge as he beat out thunderbolts for Jupiter, king of the gods, and weapons for Mars, the god of war. In Polynesia the people attributed eruptive activity to the beautiful but wrathful Pele, Goddess of Volcanoes, whenever she was angry or spiteful. Today we know that volcanic eruptions are not super-natural but can be studied and interpreted by scientists. The Nature of Volcanoes Volcanoes are mountains, but they are very different from other mountains; they are not formed by folding and crumpling or by uplift and erosion. Instead, volcanoes are built by the accumulation of their own eruptive products — lava, bombs (crusted over lava blobs
