Kirk Martini Brief Chronology of the 79 Eruption A sattelite image of the region surrounding Mt. Vesuvius. This chapter reviews that chronololgy and identifies potential consequences on the buildings of Pompeii. The term Plinian derives from the name of Pliny the Younger, whose written observations of the 79 eruption form an important part of the historic record of Pompeii. This phase created a rain of ash and pumice over a broad area primarily to the south of Vesuvius, carried by prevailing winds. There are several terms in volcanology to describe various types and aspects of this type of eruption.
Pyroclastic flows can move at high speeds along the ground and pass over substantial obstacles.
Their distribution is, however, strongly controlled by topography. A turbulent cloud of volcanic ash and hot gasses, which hugs the ground and travels at speeds often exceeding 100 km per hour. Surge deposits are more widely distributed than pyroclastic flow deposits, although not as widespread as air-fall pumice layers. The key basis for distinction is the amount and nature of the pyroclastic material included in the mixture of volcanic solids and gas. Denser mixtures which include larger fragments at higher solid concentrations are typically categorized as pyroclastic flow, while less dense mixtures where the pyroclasts are primarily fine dust and ash are categorized as pyroclastic surge.