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Fontana Tephra: A basaltic Plinian eruption in Nicaragua

By
Heidi Wehrmann
Heidi Wehrmann
1
SFB 574 at Kiel University, Wischhofstr. 1-3, 24148 Kiel, Germany
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Costanza Bonadonna
Costanza Bonadonna
2
Department of Geology, University of South Florida, 4202 East Fowler Ave, Tampa, Florida, 33620, USA, and Department of Geology and Geophysics, School of Ocean and Earth Science and Technology, University of Hawaii at Manoa, 1680 East-West Road, POST Building 617a, Honolulu, Hawaii 96822, USA
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Armin Freundt
Armin Freundt
3
IfM-GEOMAR (Leibniz Institute of Marine Sciences), RD4, Wischhofstr. 1-3, 24148 Kiel, Germany, and SFB 574 at Kiel University, Wischhofstr. 1-3, 24148 Kiel, Germany
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Bruce F. Houghton
Bruce F. Houghton
4
Department of Geology and Geophysics, School of Ocean and Earth Science and Technology, University of Hawaii at Manoa, 1680 East-West Road, POST Building 617a, Honolulu, Hawaii 96822, USA
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Steffen Kutterolf
Steffen Kutterolf
5
SFB 574 at Kiel University, Wischhofstr. 1-3, 24148 Kiel, Germany
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Published:
January 01, 2006

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.

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Contents

GSA Special Papers

Volcanic Hazards in Central America

William I. Rose
William I. Rose
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Gregg J.S. Bluth
Gregg J.S. Bluth
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Michael J. Carr
Michael J. Carr
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John W. Ewert
John W. Ewert
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Lina C. Patino
Lina C. Patino
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James W. Vallance
James W. Vallance
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Geological Society of America
Volume
412
ISBN print:
9780813724126
Publication date:
January 01, 2006

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