1 Volcanoes Volcano Cam

2 Different Volcanic Settings

3 EFFUSIVE ERUPTIONS Generally at hot spots, spreading plates Mantle comes directly to surface Hot lava; low viscosity, flows easily, gases escape easily Forms shields, flood basalts

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5 EXPLOSIVE ERUPTIONS Found at subduction zones Magma low temp (800 degrees C), high viscosity, does not flow easily, gases trapped, hard to predict explosions Forms composite volcanoes, cinder cones, calderas, aerial bombs, gas flows, very destructive

6 Shield and Composite Volcanoes Figure 12.32

7 Shield Volcanoes broad, gently sloping cones constructed of solidified lava flows lava spreads widely and thinly due to its low viscosity produces a volcano in the shape of a flattened dome or ‘shield’

8 Composite Volcanoes constructed of alternating layers of pyroclastics (ash) and rock solidified from lava flows. built over long spans of time eruption is intermittent, (a few years of intense activity separated by hundreds or thousands of years of inactivity) most of the better known volcanoes of the world are composite volcanoes.

9 Composite Volcanoes

10 Columbia River basalt flow (Ancient Shield) Composite Volcano

11 Pyroclastic Flows Superheated gas and particles (ash & dust or larger cinders, blocks or bombs) At Mt. St. Helens’s the pyroclastic flow extended up to 8 km with a temp of 700 C Mount Pelee, (Carribean island of Martinique) eruption killed all but 2 of the more than 20,000 people in the town of St. Pierre

12 MOUNT ST. HELEN’S Before 1980 Eruption May 18, 1980 After 1980 Eruption

13 Mt. Pelee

14 Ashfall Ash from eruptions that falls on surrounding ground When ash is carried to high altitudes this can spread great distances

15 Mt. Pinatubo Philippines June 1991

16 Volcanoes & Environment brilliant sunsets and sunrises due to fine ash and gases in the stratosphere, (cloud drifts around world) Mt. Pinatubo - 22 million tons of sulfur dioxide (SO 2 ) formed droplets of sulfuric acid blocked some sunlight from reaching Earth, cooling temperatures worldwide by 0.5 C An eruption the size of Mount Pinatubo could affect the weather for a few years.

17 August 26,1883, Eruption destroyed much of the island of Krakatau ("Krakatoa") in Indonesia, One of the most catastrophic natural disasters in recorded history (heard more than 3000 miles away) Fine ashes from the eruption were carried by upper level winds as far away as New York City. Volcanic dust in the upper atmosphere affected incoming solar radiation and the earth's weather for several years. ANAK KRAKATAU: (Child of Krakatoa)

18 series of large tsunami waves followed main explosion, some nearly 40 meters above sea level more than 36,000 people in the coastal towns and villages killed Tsunami waves were recorded or observed throughout the Indian Ocean, the Pacific Ocean, the American West Coast, South America, and even as far away as the English Channel.

19 April Tambora Volcano, Indonesia the most powerful eruption in recorded history. Tambora's volcanic cloud lowered global temperatures by as much as 3 C Even a year after the eruption, most of the northern hemisphere experienced sharply cooler temperatures during the summer months. In parts of Europe and in North America, 1816 was known as "the year without a summer."

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22 Mt. St. Helen’s - Oct. 1, 2004 Mt. St. Helen’s - Oct. 5, 2004

23 Mt. St. Helen’s Oct. 12, 2004 Mt. St. Helen’s Today