JOURNAL OF GEOPHYSICAL RESEARCH: SOLID EARTH, VOL. 118, 4361–4377, doi:10.1002/jgrb.50289, 2013
Magma storage and migration associated with the 2011–2012 El Hierro eruption: Implications for crustal magmatic systems at oceanic island volcanoes Pablo J. González,1 Sergey V. Samsonov,2 Susi Pepe,3 Kristy F. Tiampo,1 Pietro Tizzani,3 Francesco Casu,3 José Fernández,4 Antonio G. Camacho,4 and Eugenio Sansosti 3 Received 11 March 2013; revised 8 July 2013; accepted 10 July 2013; published 6 August 2013.
[1] Starting in July 2011, anomalous seismicity was observed at El Hierro Island, a young
oceanic island volcano. On 12 October 2011, the process led to the beginning of a submarine NW-SE fissural eruption at ~15 km from the initial earthquake loci, indicative of significant lateral magma migration. Here we conduct a multifrequency, multisensor interferometric analysis of spaceborne radar images acquired using three different satellite systems (RADARSAT-2, ENVISAT, and COSMO-SkyMed (Constellation of Small Satellites for Mediterranean Basin Observation)). The data fully captures both the pre-eruptive and coeruptive phases. Elastic modeling of the ground deformation is employed to constrain the dynamics associated with the magmatic activity. This study represents the first geodetically constrained active magmatic plumbing system model for any of the Canary Islands volcanoes, and one of the few examples of submarine volcanic activity to date. Geodetic results reveal two spatially distinct shallow (crustal) magma reservoirs, a deeper central source (9.5 ± 4.0 km), and a shallower magma reservoir at the flank of the southern rift (4.5 ± 2.0 km). The deeper source was recharged, explaining the relatively long basaltic eruption, contributing to the observed island-wide uplift processes, and validating proposed active magma underplating. The shallowest source may be an incipient reservoir that facilitates fractional crystallization as observed at other Canary Islands. Data from this eruption supports a relationship between the depth of the shallow crustal magmatic systems and the long-term magma supply rate and oceanic lithospheric age. Such a relationship implies that a factor controlling the existence/depth of shallow (crustal) magmatic systems in oceanic island volcanoes is the lithosphere thermomechanical behavior. Citation: Gonza´lez, P. J., S. V. Samsonov, S. Pepe, K. F. Tiampo, P. Tizzani, F. Casu, J. Ferna´ndez, A. G. Camacho, and E. Sansosti (2013), Magma storage and migration associated with the 2011–2012 El Hierro eruption: Implications for crustal magmatic systems at oceanic island volcanoes, J. Geophys. Res. Solid Earth, 118, 4361–4377, doi:10.1002/jgrb.50289.
1.
Introduction
[2] A deeper understanding of the magma plumbing system is critical to our ability to forecast the eruptive behavior of a volcano and to provide a wider framework to constrain dynamic volcanic processes, such as magma storage, supply rate, and migration [Takada, 1989; Poland et al., 2012; Clague Additional supporting information may be found in the online version of this article. 1 Department of Earth Sciences, University of Western Ontario London, Ontario, Canada. 2 Canada Centre for Remote Sensing, Natural Resources Canada Ottawa, Ontario, Canada. 3 Istituto per il Rilevamento Elettromagnetico dell’Ambiente, National Research Council of Italy Naples, Italy. 4 Instituto de Geociencias, CSIC, UCM Madrid, Spain. Corresponding author: P. J. González, Department of Earth Sciences, University of Western Ontario, Biological and Geological Sciences Building, 1151 Richmond St. London, ON N6A 5B7, Canada. (
[email protected]) ©2013. American Geophysical Union. All Rights Reserved. 2169-9313/13/10.1002/jgrb.50289
and Dixon, 2000, Fialko and Rubin, 1998]. Attempts to understand the structure and dynamics of magma plumbing systems at basaltic intraplate oceanic island volcanoes rely heavily on a handful of well-studied volcanoes, e.g., Kilauea and Piton de la Fournaise [Tilling and Dvorak, 1993]. However, the lack of data at other volcanoes makes it difficult to extrapolate a well-constrained magma plumbing systems and dynamics that may be used as prototypes for all oceanic island volcanoes. In particular, less active volcanoes such as the Canary or Cape Verde Islands might not be described accurately by plumbing systems inferred from highly active volcanoes. [3] An image of the active magmatic plumbing system of a volcano can be obtained via the interpretation of various geological, geophysical, and geochemical data, including seismic, experimental petrology, gas emissions chemistry, and geodetic measurements [Dzurisin, 2006]. To study the long-term evolution of magmatic systems, experimental petrology provides a very valuable tool through the analysis of erupted materials [Marsh, 1996; Hansteen et al., 1998; Longpré et al., 2008]. However, at active volcanic areas, geophysical observations are an important complement,
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GONZÁLEZ ET AL.: MAGMA DYNAMICS OF EL HIERRO ERUPTION
[5] A submarine eruption off El Hierro Island started in October 2011 and ended in early March 2012 [López et al., 2012]. The 2011–2012 El Hierro eruption represents the first eruptive episode in 40 years and the first systematically wellmonitored eruption in the Canary Islands. Consequently, the analysis of data acquired during the 2011–2012 El Hierro eruption is a unique opportunity to image, for the first time, the active magmatic system of one of the Canary Islands. In addition, it provides the first opportunity to study the volcanic phenomena associated with an onshore to offshore migration of magma that culminated into an eruption. This study also contributes to our knowledge of the magmatic systems of oceanic island volcanoes.
2.
Figure 1. Map of El Hierro Island and the three rift zones (Northeastern, Western-Northwestern, and South-Southeastern) showing topography (shaded topography). Simplified geological map of El Hierro. 1.2–0.88 Ma Tiñor volcano (green), 545–176 ka El Golfo volcano (blue), and rift volcanism, preand post-El Golfo collapse in brown and red, respectively. Flank collapses are denoted with blue dashed lines. Populated areas are shown with gray polygons. Inset: El Hierro (EH) location in the Canary Islands NW off African continent. Red star indicates the approximate location of the eruption site (same in all map figures). providing constraints on magma locations and volumes. Geodetic imaging is useful to infer complex deformation processes controlled by crustal rheology. In volcanic environments, the temperature and density contrasts affect the stress distribution which controls the dynamic magmatic processes. Nonetheless, under certain assumptions (usually brittle/elastic deformation), it is possible to evaluate magma volume storage and migration beneath a volcano [Dzurisin, 2006; Poland et al., 2012]. Therefore, the ground deformation associated with an eruption allows us to constrain the magma plumbing systems, in particular at basaltic intraplate oceanic island volcanoes with low eruption rates, and compare its structure and dynamics against the prototypes. [4] Studies of the magma plumbing systems at basaltic intraplate ocean island volcanoes (e.g., Reunion, Galápagos, Hawaiian, Canarian, and Cape Verde Islands) have revealed fundamental differences in their shallower (crustal) levels. It has been postulated that shallow (crustal) magma chambers are not always present and differ in magmatic processes. At Hawaii, magma chambers stagnate and distribute magma along elongated rift zones [Tilling and Dvorak, 1993]. However, at Tenerife and Gran Canaria Islands, crustal magma chambers develop as long-lived features that can fractionate parental basanitic composition melts into endmember (highly explosive) phonolitic magmas [Ablay and Martí, 2000]. Nevertheless, multiple processes such as flank instability also can play a role in the absence/presence of magma reservoirs by occasionally disrupting the volcanic plumbing system [e.g., Amelung and Day, 2002; Ruch et al., 2012]. Therefore, a deeper understanding of the crustal portion of the plumbing systems of oceanic island volcanoes is essential for improving volcanic risk analysis.
El Hierro Island and the 2011–2012 Eruption
[6] El Hierro Island is small basaltic oceanic island volcano with a subaerial edifice ~20 km in diameter and steep relief, with maximum altitudes of 1500 m (Pico de Malpaso) above the surrounding seafloor and bathymetry of approximately 3600–3800 m. Located in the Canary Islands volcanic archipelago, off the African continent (Figure 1), El Hierro is the south-westernmost and the youngest island, at 1.1 Ma old [Carracedo et al., 2001]. Geologically, El Hierro is composed of three overlapping units (Tiñor, El Golfo, and rift volcanism) which have suffered four flank collapses [Masson et al., 2002; Muenn et al., 2006]. The oldest formation is the Tiñor shield volcano, with activity spanning 1.2–0.88 Ma. It has been inferred that this volcano collapsed northward. Later, another shield volcano, El Golfo, completely covered the Tiñor collapse [Carracedo et al., 2001]. Eventually, El Golfo volcano again collapsed toward the north, forming the El Golfo flank collapse (87–39 ka), a prominent embayment in the north (Figure 1) [Longpré et al., 2011]. Over the last 158 ka, volcanism has been presented as effusive along three major rift zones (northeastern, west-northwestern, and southern), with the development of strombolian cinder cones and associated lava flows (Figure 1). At El Hierro, Holocene volcanism is limited to a few dated eruptions; Tanganasoga volcano, a composite volcano that erupted crystal-rich ankaramite lavas, and the Montaña Chamuscada volcano, 4000 and 2500 years before present, respectively [Guillou et al., 1996; Manconi et al., 2009]. For the last 500 years, which corresponds with the historical record, no volcanic eruptions have been confirmed. In 1793, a felt seismic crisis was dubiously associated with the eruption of the Lomo Negro volcano, northwest of the island [Carracedo et al., 2001; Romero and Guillén, 2012]. Over the past decade, seismicity has remained low, with an average seismicity rate of
