Fontana Tephra: A basaltic Plinian eruption in Nicaragua

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.