UNDERSTANDING VOLCANOS PowerPoint Presentation

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UNDERSTANDING VOLCANOS Dr. Walter Hays, Global Alliance For Disaster Reduction

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ESSENTIAL KNOWLEDGE FOR SOCIETAL SUSTAINABILITY A FRAMEWORK FOR UNDERSTANDING THE IMPACTS OF VOLCANIC ERUPTIONS ON PEOPLE AND THEIR COMMUNITIES

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GLOBAL DISTRIBUTION OF 1,500 ACTIVE VOLCANOES

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ERUPTIONS OF MOUNT MERAPI May 15, and June 6 - 8, 2006

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LOCATION IN CENTRAL JAVA

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MOUNT MERAPI RECEIVED CLOSE ATTENTION ON APRIL 18

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INDONESIA’S MOUNT MERAPI ERUPTED ON MAY 15, 2006 Mount Merapi, a stratovolcano, emitted lava, debris, and a pyroclastic flow (or cloud) on May 15.

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MAY 15, 2006 ERUPTION Hot ash released.

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MAY 15, 2006 ERUPTION Volcanic ash turned everything white

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MAY 15, 2006 ERUPTION School children wore masks to counter adverse health effects of breathing volcanic ash.

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MAY 15, 2006 ERUPTION Volcanic ash covered crops and vegetation.

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MAY 15, 2006 ERUPTION Volcanic ash covered automobiles and affected jet airline traffic.

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MOUNT MERAPI ERUPTED AGAIN ON JUNE 6-8, 2006 Mount Merapi volcano emitted lava, debris, and pyroclastic flows (superheated clouds of gas) on Tuesday, June 6 and Wednesday, June 7.

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EXPLOSIVENESS OF JUNE 8 ERUPTION SENT 15,000 FLEEING

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EVACUATION 11,000 from three districts evacuated to schools and otheren “safe haven” emer-gency shelters.

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MANY CHOSE TO EVACUATE Many citizens chose to evacuate. Evacuation was ordered. Villagers remembered the 1994 disaster.

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MANY CHOOSE NOT TO EVACUATE Many citizens chose not to evacuate because shelters are boring and they wanted to provide for livestock and tend crops.

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ESSENTIAL KNOWLEDGE ON VOLCANOES

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Plate tectonics and volcanic activity Global distribution of volcanoes Most volcanoes are located within or near ocean basins Basaltic rocks: in oceanic and continental settings Granitic rocks: in continental settings

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The nature of volcanic eruptions Three physical characteristics of a magma control its viscosity, the physical property that ultimately determines the “violence” or explosiveness, of the eruption: Composition Temperature Dissolved gases

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The magma affects the severity of a volcanic eruptions In summary Basaltic Magmas = mild eruptions Rhyolitic or Andesitic Magmas = explosive eruptions

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The nature of volcanic eruptions Viscosity is a measure of a material’s resistance to flow Factors affecting viscosity Temperature - Hotter magmas are less viscous Composition - Silica (SiO2) content

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The nature of volcanic eruptions Higher silica content = higher viscosity (e.g., felsic lava such as rhyolite) Lower silica content = lower viscosity (e.g., mafic lava such as basalt)

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The nature of volcanic eruptions Dissolved gases Gas content affects magma mobility Gases expand within a magma as it nears the Earth’s surface due to decreasing pressure The violence of an eruption is related to how easily gases escape from magma

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Materials extruded from a volcano Lava flows Basaltic lavas exhibit fluid behavior Types of basaltic flows Pahoehoe lava (resembles a twisted or ropey texture) Aa lava (rough, jagged blocky texture) Dissolved gases 1% - 6% by weight Mainly H2O and CO2

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Materials extruded from a volcano Pyroclastic materials – “fire fragments” Types of pyroclastic debris Ash and dust - fine, glassy fragments Pumice - porous rock from “frothy” lava Cinders - pea-sized material

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Materials extruded from a volcano (continued) Pyroclastic materials – “fire fragments” Types of pyroclastic debris Lapilli - walnut-sized material Particles larger than lapilli Blocks - hardened or cooled lava Bombs - ejected as hot lava

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Volcanoes General features Opening at the summit of a volcano Crater - summit depression < 1 km diameter Caldera - summit depression > 1 km diameter produced by collapse following a massive eruption Vent – surface opening connected to the magma chamber Fumarole – emit only gases and smoke

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Volcanoes Types of volcanoes Shield volcano Broad, slightly domed-shaped Generally cover large areas Produced by mild eruptions of large volumes of basaltic lava Example: Mauna Loa on Hawaii

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Volcanoes Cinder cone Built from ejected lava (mainly cinder-sized) fragments Steep slope angle Small size Frequently occur in groups

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Volcanoes Composite cone (stratovolcano) Most are located adjacent to the Pacific Ocean (e.g., Fujiyama, Mt. St. Helens) Large, classic-shaped volcano (1000’s of ft. high and several miles wide at base)

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Mt. St. Helens – prior to the 1980 eruption

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Mt. St. Helens (after the 1980 eruption)

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Volcanoes Composite cone (stratovolcano) -continued Composed of interbedded lava flows and pyroclastic debris Most violent type of activity (e.g., Mt. Vesuvius)

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Volcanic Hazards Nuée ardente – A Fiery pyroclastic flow made of hot gases infused with ash and other debris Also known as “glowing avalanches” Move down the slopes of a volcano with velocities approaching 200 km/hour

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Volcanic Hazards Lahar – volcanic landslide or mudflow Mixture of volcanic debris and water Move down slopes of volcano and stream valleys with velocities of 30 to 60 miles/hour

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volcanic hazards Pyroclastic flow Felsic and intermediate magmas Consists of ash, pumice, and other debris Material ejected at high velocities Example: Yellowstone plateau

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Other volcanic landforms Caldera Steep-walled depressions at the summit Generally > 1 km in diameter Produced by collapse Example: Crater Lake, Oregon

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Other volcanic landforms Fissure eruptions and lava plateaus Fluid basaltic lava extruded from crustal fractures called fissures Example: Columbia River Plateau Lava domes Bulbous mass of congealed lava Associated with explosive eruptions of gas-rich magma

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Other volcanic landforms Volcanic pipes and necks Pipes - short conduits that connect a magma chamber to the surface Volcanic necks (e.g., Ship Rock, New Mexico) - resistant vents left standing after erosion has removed the volcanic cone

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Shiprock, New Mexico

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Intrusive igneous activity Most magma is emplaced at depth in the Earth Once cooled and solidified, it is called a pluton

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Intrusive igneous activity Nature of plutons Shape - tabular (sheetlike) vs. massive Orientation with respect to the host (surrounding) rock Concordant vs. discordant

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Intrusive igneous activity Types of intrusive igneous features Dike – a tabular, discordant pluton Sill – a tabular, concordant pluton (e.g., Palisades Sill in New York)

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Intrusive igneous activity Types of intrusive igneous features Lacolith Similar to a sill Lens or mushroom-shaped mass Arches overlying strata upward

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Intrusive igneous activity Intrusive igneous features continued Batholith Largest intrusive body Surface exposure > 100+ km2 (smaller bodies are termed stocks) Frequently form the cores of mountains

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Plate tectonics and igneous activity Global distribution of igneous activity Most volcanoes are located within or near ocean basins Basaltic rocks: oceanic and continental settings Granitic rocks: continental settings

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Plate tectonics and igneous activity Igneous activity at plate margins Spreading centers Greatest volume of volcanic rock is produced along the oceanic ridge system

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Plate tectonics and igneous activity Igneous activity at plate margins Mechanics of spreading Decompression melting of the mantle occurs as the lithosphere is pulled apart Large quantities of basaltic magma are produced

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Plate tectonics and igneous activity Subduction zones Occur in conjunction with deep oceanic trenches Location of partial melting of descending plate and upper mantle Rising magma can form either An island arc if in the ocean A volcanic arc if on a continental margin

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Plate tectonics and igneous activity Subduction zones are associated with the Pacific Ocean Basin The region representing the Pacific Rim is known as the “Ring of Fire” Location of majority of world’s explosive volcanoes

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Plate tectonics and igneous activity Intraplate volcanism Occurs within a tectonic plate Associated with mantle plumes Localized volcanic regions in the overriding plate are called a hot spot Produces basaltic magma sources in oceanic crust (e.g., Hawaii and Iceland) Produces granitic magma sources in continental crust (e.g., Yellowstone Park)

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Volcanoes and climate The basic premise Explosive eruptions emit huge quantities of gases and fine-grained debris A portion of the incoming solar radiation is reflected and filtered out

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Volcanoes and climate Past examples of volcanism affecting climate Mount Tambora, Indonesia – 1815 Krakatau, Indonesia – 1883

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Volcanoes Can Impact Regional And Global Climate Modern examples Mount St. Helens, Washington - 1980 El Chichón, Mexico - 1982 Mount Pinatubo, Philippines - 1991