I fenomeni vulcanici - Sei

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132 I FENOMENI ENDOGENI CONTENT AND LANGUAGE INTEGRATED LEARNING CLIL Short-Term Prediction In contrast to regional predictions, short-term predictions attempt to forecast the specific time and place of an impending eruption. They are based on instruments that monitor an active volcano to detect signals that the volcano is about to erupt. The signals include changes in the shape of the mountain and surrounding land, earthquake swarms indicating movement of magma beneath the mountain, increased emissions of ash or gas, increasing temperatures of nearby hot springs, and any other signs that magma is approaching the surface. In 1978, two U.S. Geological Survey (USGS) geologists, Dwight Crandall and Don Mullineaux, noted that Mount St. Helens had erupted more frequently and violently during the past 4,500 years than any other volcano in the contiguous 48 states. They predicted that the volcano would erupt again before the end of the century. In March 1980, about two months before the great May eruption, puffs of steam and volcanic ash rose from the crater of Mount St. Helens, and swarms of earthquakes occurred beneath the mountain. This activity convinced other USGS geologists that Crandall and Mullineaux’s prediction was correct. In response, they installed networks of seismographs, tiltmeters, and surveying instruments on and around the mountain. 2 Aerial view of pyroclastic flow deposits from the Mount Pinatubo eruption 1991. Swarm: fig. a group of bees Ash: the grey substance left when something is burnt completely Nearby: that is a short distance away Steam: the gas or vapour that rises from boiling water In the spring of 1980, the geologists warned government agencies and the public that Mount St. Helens showed signs of an impending eruption. The U.S. Forest Service and local law enforcement officers quickly evacuated the area surrounding the mountain, averting a much larger tragedy. Using similar kinds of information, geologists predicted the 1991 Mount Pinatubo eruption in the Philippines, saving many lives 2 . Although the June 25, 1997, eruption of the Soufrière Hills volcan on the Caribbean island of Montserrat killed 19 people and destroyed many homes and farms, predictions of the eruption by the Montserrat Volcano Observatory saved many additional lives. The island was long known to harbor an active volcano, and the observatory was established to monitor the volcano and to predict eruptions. The observatory recorded continued swelling of the dome, swarms of earthquakes, and many large and small eruptions, including pyroclastic flows, through the rest of 1996 and the first half of 1997. On June 25, 1997, major pyroclastic flows reached to within 50 meters of the airport. Surges and flows devastated several communities, killing 19 people. Although some people returned to homes and farms during lulls in the long eruptive sequence, there is little doubt that the warnings issued by the observatory and evacuations ordered by the government saved many lives. True or false from Thompson-Turk, Earth Science and Environment, 4E. © 2007. 1. Regional predictions attempt to forecast the specific time and place of an impending eruption. T F 2. The potential violence of a volcanic eruption is related to the geological environment of the volcano. T F 3. Earthquake swarms, emissions of ahes and gases and puffs of steam are important signal in short-term prediction of volcanic eruptions. T F 4. Short-time predictions always save human lives. T F 5. If an active volcano lies on continental crust, the eruption may be gentle because granitic magma may form. T F 6. If an active volcano lies on oceanic crust, the eruption may be gentle because basaltic magma may form. T F to Harbor: fig. to host Dome: the rounded summit of a hill or mountain; (geology) a rounded uplifted landform or underground structure Lull: a temporary period of quiet or inactivity © SEI – 2012
© SEI – 2012 attivi (circa 600) estinti quiescenti possono essere se il magma NON SALE in superficie attività ignea INTRUSIVA PLUTONI BATOLITI FILONI LACCOLITI PER RIPASSARE VULCANESIMO = forza endogena di modificazione della superficie terrestre MAGMI SIALICI INTERMEDI FEMICI basaltiche andesitiche riolitiche VISCOSITÀ SILICE EFFUSIVE i magmi sono fluidi i condotti restano liberi i gas non si accumulano concentrati in fasce lunghe e strette se il magma SALE in superficie attività ignea EFFUSIVA ERUZIONI materiali emessi 6 I <strong>fenomeni</strong> <strong>vulcanici</strong> DORSALI OCEANICHE ARCHI DI ISOLE E ALCUNI MARGINI CONTINENTALI FRATTURE CONTINENTALI VULCANI ISOLATI (PUNTI CALDI) CENTRALI LINEARI ESPLOSIVE i magmi sono viscosi i condotti si ostruiscono i gas si accumulano LAVE PIROCLASTI GAS a corda a blocchi a cuscino polveri ceneri lapilli bombe EDIFICIO VULCANICO il magma fuoriesce dal camino il magma fuoriesce dalle fratture PLATEAUX E DORSALI 133
Page 1 and 2: © SEI - 2012 I fenomeni vulcanici
Page 3 and 4: © SEI - 2012 6 I fenomeni vulcanic
Page 5 and 6: © SEI - 2012 3 I corpi magmatici i
Page 7 and 8: © SEI - 2012 La struttura L’atti
Page 9 and 10: © SEI - 2012 Le lave: forme e stru
Page 11 and 12: © SEI - 2012 Sono colate piroclast
Page 13 and 14: © SEI - 2012 ■ I coni di scorie
Page 15 and 16: © SEI - 2012 ■ Eruzioni freatich
Page 17 and 18: © SEI - 2012 Strettamente legati a
Page 19 and 20: © SEI - 2012 9 L’attività vulca
Page 21 and 22: © SEI - 2012 La provincia magmatic
Page 23 and 24: © SEI - 2012 10 Il pericolo e il r
Page 25: © SEI - 2012 Risk Assessment: Pred
Page 29 and 30: © SEI - 2012 VERIFICA Definisci vu

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