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Book Chapter

Gravity and geodesy of Concepción Volcano, Nicaragua

By
José Armando Saballos
José Armando Saballos
Department of Geology, University of South Florida, 4202 E. Fowler Avenue, SCA528, Tampa, Florida 33620, USA
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Rocco Malservisi
Rocco Malservisi
Department of Geology, University of South Florida, 4202 E. Fowler Avenue, SCA528, Tampa, Florida 33620, USA
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Charles B. Connor
Charles B. Connor
Department of Geology, University of South Florida, 4202 E. Fowler Avenue, SCA528, Tampa, Florida 33620, USA
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Peter C. La Femina
Peter C. La Femina
Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16802, USA
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Paul Wetmore
Paul Wetmore
Department of Geology, University of South Florida, 4202 E. Fowler Avenue, SCA528, Tampa, Florida 33620, USA
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Published:
November 2013

Concepción is currently the most active composite volcano in Nicaragua. Ash explosions of small to moderate size (volcano explosivity index 1–2) have occurred on a regular basis. Gravity data collected on and around the volcano between 2007 and 2010 confirm that a younger cone is built atop an older truncated edifice of denser material, predominantly lavas. The bulk density of the volcanic cone is 1764 kg m−3 (with an uncertainty of at least ±111 kg m−3), derived from gravity data. This estimated bulk density is significantly lower than densities (e.g., 2500 kg m−3) used in previous models of gravitational spreading of this volcano and suggests that the gravitational load of the edifice may be much lower than previously thought. The gravity data also revealed the existence of a possible northwest-southeast–oriented normal fault (parallel to the subduction zone). Episodic geodetic data gathered with dual-frequency global positioning system (GPS) instruments at five sites located around the volcano's base show no significant change in baseline length during 8 yr and 2 yr of observations along separate baselines. Structures deformed after the Tierra Blanca Plinian eruption ca. 19 ka, which significantly altered the form and bulk density of the volcano, may be due to the spreading of the volcano, but may also be related to volcano loading, magmatic intrusions and their subsequent evolution, and other volcano-tectonic processes, or a combination of any of these factors. A joint interpretation of our gravity and geodetic GPS data of Concepción suggests that this volcano is not spreading in a continuous fashion; if it is episodically spreading, it is driven by magma intrusion rather than gravity. These results have important implications for volcanic hazards associated with Concepción Volcano. Although during the last 15 yr tephra fallout and volcanic debris flows (lahars) have been the pervasive hazards at this volcano, earthquakes from an eventual slip of the fault on the east-northeast side of the volcano (delineated from our gravity measurements) should be considered as another important hazard, which may severely damage the infrastructures in the island, and conceivably trigger a volcano flank collapse.

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Contents

GSA Special Papers

Understanding Open-Vent Volcanism and Related Hazards

Edited by
William I. Rose
William I. Rose
Geological Engineering & Sciences, Michigan Technological University, Houghton, Michigan 49931, USA
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José Luis Palma
José Luis Palma
Departamento de Ciencias de la Tierra, Universidad de Concepción, Victor Lamas 1290, Concepción, Chile
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Hugo Delgado Granados
Hugo Delgado Granados
Instituto de Geofísica, Universidad Nacional Autónoma de México Circuito Científico, C.U. Coyoacán 04510, México, D.F.
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Nick Varley
Nick Varley
Facultad de Ciencias, Universidad de Colima, Avenida Universidad 333, Colonia Las Víboras, C.P. 28040, Colima, México
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Geological Society of America
Volume
498
ISBN print:
9780813724980
Publication date:
2013

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