LYCOS RETRIEVER 
Volcanoes: Eruptions
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Volcanoes located within the densely cratered southern highlands have a very different morphology from either the Tharsis or Elysium volcanoes. Tyrrhena Patera has very little vertical relief (< 2 kilometers), resulting in very shallow flank slopes. The flanks of the volcano are deeply eroded with many broad channels that radiate from the summit region. The low relief and easily erodible nature of the flank materials has been interpreted to indicate that the bulk of the volcano is composed of pyroclastic ash deposits. This interpretation implies that the style of eruption for the highland volcanoes like Tyrrhena Patera is significantly different from the repeated effusion of fluid lavas that built up the shield volcanoes. (Copyright Calvin J. Hamilton; caption by LPI)
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Volcanoes come in different shapes and sizes depending on the makeup of the magma, the style of the eruption, and how often they erupt. The major types of volcanoes are cinder cones, shield volcanoes, caldaria and plateaus. Calderas and plateaus are shaped differently than traditional volcanoes neither has a mountain like shape
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The two principal volcanoes in the United States are Mauna Loa and Kilauea, both in the Hawaiian island chain. Mauna Loa, the world's largest volcano, erupted most recently in 1975 and 1984. Kilauea is in almost continual eruption. Alaskan eruptions occurred in 1989, when Mount Redoubt, along Cook Inlet, southwest of Anchorage, erupted; in 1992, when Mount Spurr erupted; and in 1996, when an unnamed volcano on Augustine Island (... in Cook Inlet) erupted. Although not in the United States, Mount Pinatubo in the Philippines projected enough ash into the stratosphere during its eruption in 1991 to have a significant cooling effect on the U.S. climate for several years. Eruptions in the lower forty-eight states are rare but certainly not unknown: for example, the widely publicized eruption of Mount St. Helens in Washington State in 1980.
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Volcanoes form when chambers of magma, or hot molten rock, boil to the surface. These magma chambers often remain sealed for hundreds of years between eruptions, until the pressure builds sufficiently to break through a vent, which is a crack or weak spot in the rock above.
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The current eruption originates from a fissure northeast of Pu'u Ô'ô vent, in the Pu'u Kahauale'a Natural Area Reserve, outside the boundaries of Hawai'i Volcanoes National Park. The area is managed by the Department of Land and Natural Resources, and is strictly off limits for public safety concerns due to hazardous vent conditions and high sulfur dioxide fume concentrations, with ongoing law enforcement to prevent entry. Outside of the Natural Area Reserve, the coastal land area near the current flow is ... strictly off limits and state officials are redirecting hikers to the lava viewing area.
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Supervolcano is the popular term for large volcanoes that usually have a large caldera and can potentially produce devastation on an enormous, sometimes continental, scale. Such eruptions would be able to cause severe cooling of global temperatures for many years afterwards because of the huge volumes of sulfur and ash erupted. They can be the most dangerous type of volcano. Examples include Yellowstone Caldera in Yellowstone National Park and Lake Toba in Sumatra, Indonesia. Supervolcanoes are hard to identify given their enormous areas covered. They are ... known as flood basalt events due to the large amounts of basalt ejected.
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Eruptions