mar110 lecture #7 volcanoes ii - smast.umassd.edu

MAR 110: Lecture 7 Outline –Volcanoes II

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MAR110 LECTURE #7

Volcanoes II

Super volcanoes (sometimes referred to a mega volcanoes) are gigantic volcanoes that are many times more powerful than both Krakatoa and Tambora combined. The second most recent one to erupt was Toba 74,000 years ago in Sumatra and was thought to have triggered an ice age. The mass extinction that followed from the sudden drop in temperature as well as from the ash and other fallout could have wiped out as much as three fourths of all the life on the planet. (SA??)


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There are at least three known super volcanoes in the United States. The directly affected regions for each is shown with Mount Saint Helens shown for comparison. Note the relative amounts of debris. (SA??)

A volcano ejects ash into the stratosphere where the winds distribute it before

eventually falling out, sometimes after several years. (NG??)


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Large amounts of fine volcanic ash are ejected during an eruption can burn and/or smother life near the volcano as it settles. Farther away the fine dust can coat everything and cause roofs to collapse from the excessive weight of only a few centimeters. Even small amounts of the ash when breathed in can also damage lungs and other tissues. (??)


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Volcanic ash and dust in the stratosphere reflects sunlight back into space (top). This reduction in the amount of sunlight reaching the earth creates a cooling effect. Krakatoa’s eruption released enough ash into the atmosphere to cause noticeable cooling (bottom). Also note Tambora in 1815, that eruption released even more ash than Krakatoa and combined with ash from the unusually high number of other volcanoes that erupted at the same year, the cooling effect was extreme compared to other events. (??, NH)


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Interior heat escape causes convection cells, with hotter rising plumes and the cooler sinking plumes to form. The lithospheric plates at the surface move with the lateral flow that connects the plumes. The movement of the electrically-conducting mantle material in the convection cells creates the earth’s magnetic field (?)


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A hotspot is an area under the earth’s crust where an isolated, stationary plume of magma rises to the surface forming a volcanic island. As the plate moves relative to the stationary plume, the volcano is cut off from its source of magma it becomes extinct. A new volcanic island then begins to form – repeating the cycle, thereby building a chain of volcanic islands. (ItO)


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(A) Stationary hot spots feed magma to new volcanic island (#1) –around which a fringing reef forms. (B) The moving plate drags volcano #1 away from magma chamber rendering it extinct, while forming a new volcanic island (#2). (ItO)


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(C) The moving plate drags volcano #2 away from magma chamber rendering it extinct, while forming a new volcanic island (#3). (C) The moving plate drags volcano #3 away from magma chamber rendering it extinct, while forming a new volcanic island (#4). (ItO)


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Kilauea Volcanism Associated with the Hawaiian Hot Spot(?)

The Hawaiian Ridge is formed from a hot spot-generated volcanic island chain. Note the increasing age of the islands furthest away from the newest Hawaiian island. Also note that the direction of plate movement probably changed radically about 40 MYBP (ItO)


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The Big Island – Active Volcanism


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Hot spot island chains throughout the Pacific Basin

mar110 lecture #7 volcanoes ii - smast.umassd.edu

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