BackgroundThe San Venanzo complex consists of the San Venanzo maar and the Pian di Celle tuff ring, both part of the Umbria-Latium ultra-alkaline district. The tuff ring is also associated with two spatter cones and a scoria cone. This complex of vents lies within the Tiber Valley Graben, where magmatism is believed to be a result of extension that began during the Pliocene (Stoppa, 1996). Early on, the eruption was explosive, producing pyroclastic flows and dry lapilli surges covering an area of about 0.15 km2; later eruptive behavior was dominated by lava flows. Block collapse and debris flows led to the formation of the steep inner crater walls. The tuffs of both San Venanzo and Pian di Celle are calcitic to carbonatitic in composition, and have been dated at about 265 +/- 3 ka (Stoppa, 1996; Stoppa and Sforna, 1995).
Smithsonian / GVP volcano information
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