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Explosive Materials. The greater the explosivity, the greater the amount of fragmentation Lava & rock material sent into the air is called Tephra : ( Greek, for ash) is a generic term for any airborne pyroclastic accumulation
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Explosive Materials • The greater the explosivity, the greater the amount of fragmentation • Lava & rock material sent into the air is called Tephra : (Greek, for ash) is a generic term for any airborne pyroclasticaccumulation Pyroclastic flows: (fire fragments) Individual eruptive fragments are called
Tephra : Classified by size LAPILLI-- Pea- to walnut-size (2 to 64 mm). They often look like cinders ASH -- Very fine-grained fragments (< 2 mm), generally dominated by broken glass shards
Pyroclastic flows • move at speeds of over 60 miles per hour • reach temperatures of over 800 Degrees Fahrenheit (400 degrees Celsius).
Hazards of Volcanoes • Lava flows- consume land unable to rebuild • Ash falls – smother towns and countryside; health hazard • Pyroclastic flows – incinerate surrounding areas • Marine eruptions – tsunamis • Invisible gases – asphyxiation • Effect on climate – Tambora 1815; 1816 "year without Summer"
When archaeologists began excavating Pompeii, they found unusual spaces in the ash layer that, when filled with plaster, were casts of people that had been caught by the volcanic debris flow and could not escape.