Lec 12 - W 9 Tues - Volcanic activity hazards

felsic because its light coloured pumis rock froth

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Unformatted text preview: alls Clouds of pumice, fine-grained ash and acidic gases are propelled vertically, high into atmosphere. - felsic because it's LIGHT coloured - pumis = rock froth (soap = lava) Larger particles fall close to volcano, while finer particles settle farther away. - ash = respiratory probs, basically tiny pieces of glass - ash into plane engines, melt and gum up jets Consequences of ash Falls: Destruction of vegetation Surface water acidity Health = respiratory problems Aviation problems _________ Structural damage to buildings: settling on roof causes loading and subsequent collapse Primary Volcanic Hazards: Pyroclastic Flows Nuee ardente = “glowing cloud” of hot volcanic ash, boulders and gas - sucks up oxygen - hot enough, particles melted together (ash) Temperatures 100-600oC Travel >100 km/hr down slope. Obstructions knocked down or blown away suffocation is a major hazard _________ Ash can weld together in the heat = welded tuff 9 Historical Example of Volcanic Hazard: Eruption of Vesuvius Effects of ash fall and pyroclastic flow Vesuvius A.D. 79 - mount Vesuvius: intermediate to felsic magma - left with hollows (encaged in the ash) 4 cubic km of ash erupted in 19 hrs Nearby city of Pompeii buried under 3 metres of ash Rate of ash fall 12-15 cm/hr Followed by a Nuee Ardente City of Herculaneum buried under 23 metre-thick pyroclastic flow Killed 2000 people in a matter of minutes (plaster casts depicted people in last few seconds of life) - plaster casts of the ppl who died - the shock produces sumani Pliny the Younger reported earthquakes before eruption, details of the eruption itself and a tsunami generated by the explosion. Primary Volcanic Hazards: Poisonous Gas Lake Nyos, Cameroon A Killer Lake - carbon dioxide gass build up at bottom of lake - high winds, disturbance, gas escaped, flowed down side of volcano In 1986, carbon dioxide was suddenly released from the bottom of the lake (a volcanic crater) - turned orange from oxidized iron - was invisible even though not active Denser than air, the ___ carbon dioxide flowed downslope, killing more than 1700 people and livestock up to 25 km away More dangerous than carbon dioxide (which merely suffocates) are hydrogen sulphide (which legitima...
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