Perret's Eruption Diagrams

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Perret's Eruption Diagrams

The Perret System allows an observer to chart the changing phases and relative intensity of eruptive activity. “The divisions of the circle are marked to represent the different classes of phenomena in their most general terms – explosive, effusive, seismic, etc.” When activity is strong, the volcanologist blackens more circles in the appropriate radii, less when the activity subsides. The outermost dots, when connected, reveal the overall intensity at a glance. These charts describe Vesuvius during Perret’s first six months on the scene. Vesuvius Eruption of 1906.