Fontana Tephra: A basaltic Plinian eruption in Nicaragua
Published:January 01, 2006
Heidi Wehrmann, Costanza Bonadonna, Armin Freundt, Bruce F. Houghton, Steffen Kutterolf, 2006. "Fontana Tephra: A basaltic Plinian eruption in Nicaragua", Volcanic Hazards in Central America, William I. Rose, Gregg J.S. Bluth, Michael J. Carr, John W. Ewert, Lina C. Patino, James W. Vallance
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Fontana Tephra was erupted from the Masaya area in west-central Nicaragua in the late Pleistocene. This basaltic-andesitic Plinian eruption evolved through (1) an initial sequence of short, highly explosive pulses emplacing thinly stratified fallout lapilli, (2) emplacement of a surge to the southwest while fallout took place in the northwesterly dispersal sectors, (3) a series of quasi-steady Plinian episodes depositing massive fallout beds of highly vesicular scoria lapilli, and (4) a terminal phase of the eruption comprising numerous subplinian eruption pulses in which varying amounts of external water were involved, forming a well-stratified sequence of lapilli beds. The Plinian episodes were repeatedly interrupted by phreatomagmatically affected pulses, evidenced by layers of higher lithic contents and scoria clasts with quenched rims, as well as by proximal cross-bedded fine to medium lapilli pyroclastic surge deposits, which left pale ash partings at distal locations.
Erupted tephra volumes, column heights, and wind velocities have been estimated for three different vent scenarios because no firm source location could be identified. The minimum total erupted tephra volume is between 1.4 and 1.8 km3, much lower than previous estimates for this eruption. Eruption column heights ranging from 24 to 30 km for the Plinian eruptive phases were obtained by comparing lithic and scoria distribution data with modeling results. Consistent results from different approaches suggest that these models, which were developed for dacitic to rhyolitic Plinian eruptions, also provide good approximations for basaltic Plinian eruptions considering all sources of uncertainty.