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Volcanic Eruptions Mt. Vesuvius (79AD) – Pompeii Prepared by Karissa Lee What is a volcano? • A volcano is a vent or 'chimney' that connects molten rock (magma) from within the Earth’s crust to the Earth's surface. • The volcano includes the surrounding cone of erupted material. How and why do volcanoes erupt? • Hot, molten rock (magma) is buoyant (has a lower density than the surrounding rocks) and will rise up through the crust to erupt on the surface. • Depending how magma reaches the surface, how easily it flows (viscosity) and the amount of gas (H2O, CO2, S) it has in it, determines how the volcano erupts. • Large amounts of gas and a high viscosity (sticky) magma will form an explosive eruption! • Small amounts of gas and (or) low viscosity (runny) magma will form an effusive eruption, non-explosive. • Lava flows when magma trickles out of the volcano (lava flow). Effusive and Explosive Eruptions • Effusive Eruptions • Occur when hot, (1200 °C ) runny basalt magmas reach the surface. Dissolved gases escape easily as the magma erupts, forming lava that flows downhill quite easily. • Lava flows generated by effusive eruptions vary in shape, thickness, length, and width depending on the type of lava erupted, discharge, slope of the ground over which the lava travels, and duration of eruption Kilauea Volcano, Hawaii. Lava spilling from the cone has formed a series of lava channels and flows. Effusive and Explosive Eruptions • Explosive Eruptions • Explosive volcanic eruptions is usually catastrophic • Erupts 10’s-1000’s km3 of magma • Send ash clouds >25 km into the stratosphere • Have severe environmental and climatic effects • Very Hazardous • Three products from an explosive eruption • Ash fall • Pyroclastic flow – A fast moving hot gas and rock with up to 450 mph speed and up to 1,000 °C temperature. This usually travels downhill by gravity, which can easily bury the highly populated areas under the mountain • Pyroclastic surge - a fluidized mass of turbulent gas and rock fragments which is ejected during some volcanic eruption Above: Large eruption column and ash cloud from an explosive eruption at Mt Vesuvius, Italy in March 1944 More About Pyroclastic Flows • Burns and buries such a wide range of region • Flood and Mud Slides • • • • Hot volcanic activity can melt snow and ice Melted snow and ice picks up rock and debris Forms fast flowing, high energy torrents Destroys all in its path • Ash Builds Up • Collapses roofs • Brings down power lines • Kills plants • Contaminates water supplies • Respiratory hazard for humans and animals • Vesuvius (AD79) eruption had pyroclastic flows with the above occurrences. Background Mt. Vesuvius (AD79) - Pompeii • • • • Mt. Vesuvius is located seven miles from the city of Naples in Italy. The height of the volcano has changed greatly for 200,000 years. It stands today at 1277 meters in height with a base that is 48 kilometers wide. On August 24, 79AD Mount Vesuvius literally blew its top, erupting tons of molten ash, rocks, pumice and sulfuric gas miles into the atmosphere and it continued about 19 hours. Mt. Vesuvius is a composite type of volcano, which is formed by alternating layers of lava and rock fragments The black cloud represents the general distribution of ash and cinder Negative and Positive Effects of Eruption Mt. Vesuvius (AD79) - Pompeii • Negative Effects • • It was an explosive eruption that followed by Pyroclastic flows of poisonous gas and hot volcanic debris engulfing the cities of Pompeii, Herculaneum and Stabiae, suffocating the inhabitants and burying the buildings. Positive Effects • The cities remained buried and undiscovered for almost 1700 years until excavation began in 1748. These excavations continue today and provide insight into life during the Roman Empire. Interesting Facts Mt. Vesuvius (AD79) - Pompeii • • • • • • • • • • The people of Pompeii and Herculaneum had plenty of warning signs way before the eruption. Some but not many did escape in time. Most were overcome by the gasses before the actual eruption. Because ash covered the sky, the visibility was so poor that people were disoriented and stopped in their tracks. The weight from the ash and debris collapsed most rooftops Mt. Vesuvius has been rumbling for years and no one took it seriously. Many tried to escape by sea but were overcome by the debris falling and many were found dead in caves along the coast. The forms of where bodies once lay were discovered when an excavator poked a rod into the ground and realized there were hollow cavities. Food, tools, paintings, and many other items were discovered under the packed and hardened ash. People today are still living quite near this rumbling mountain with it's rich, fertile soil. Vesuvius Today • The areas of Vesuvius was declared as a national park in 1995 by attracting thousands of visitors worldwide • Vesuvius is still regarded as an active and the most dangerous volcano in the world because it is located nearby heavily populated flanks: • • • around 1.5 million people live in the city of Naples alone Naples is situated approx. 30 km from Vesuvius Pyroclastic flows can flow up to 100 km from source THANK YOU • References • • • • • • • • • • • http://en.wikipedia.org/wiki/Volcano http://library.thinkquest.org/03oct/01550/eruptions.htm http://kids.discovery.com/tell-me/curiosity-corner/earth/naturaldisasters/why-do-volcanoes-erupt http://en.wikipedia.org/wiki/Explosive_eruption http://en.wikipedia.org/wiki/Effusive_eruption http://en.wikipedia.org/wiki/Vesuvious#Eruption_of_79 http://www.windows2universe.org/earth/interior/Mt_Vesuvius_ad79.html http://www.lovethesepics.com/2011/10/infamous-mount-vesuviusone-of-the-worlds-most-dangerous-volcanoes-41-pics/ http://vulcan.fis.uniroma3.it/vesuvio/79_eruption.html http://www.bbc.co.uk/dna/ptop/A28303968 http://en.wikipedia.org/wiki/Pyroclastic_flow