Marti Et Al 2009 Tene Crisis.Pdf

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Authors requiring further information regarding Elsevier’s archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright Author's personal copy Journal of Volcanology and Geothermal Research 182 (2009) 23–33 Contents lists available at ScienceDirect Journal of Volcanology and Geothermal Research journal homepage: www.elsevier.com/locate/jvolgeores Characterising unrest during the reawakening of the central volcanic complex on Tenerife, Canary Islands, 2004–2005, and implications for assessing hazards and risk mitigation J. Martí a,⁎, R. Ortiz b, J. Gottsmann c, A. Garcia b, S. De La Cruz-Reyna d a Institute of Earth Sciences “Jaume Almera”, CSIC, Lluís Solé Sabarís s/n, Barcelona 08028, Spain b Department of Volcanology, Museo Nacional de Ciencias Naturales, CSIC, C/ José Gutiérrez Abascal, 2, 28006 Madrid, Spain c Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 1RJ, United Kingdom d Instituto de Geofísica, Universidad Nacional Autónoma de México, Ciudad Universitaria, México 04510 D.F., México article info abstract Article history: Increased onshore seismic activity in April 2004 marked the first documented renewal of tectonic unrest on Received 13 June 2007 Tenerife, Canary Islands, Spain, since the island's last volcanic eruption in 1909. Events included tremors, felt Accepted 30 January 2009 earthquakes and the occasional emission of a visible gas plume from the central 3718 m high Teide volcano, Available online 15 February 2009 and an increased diffuse emission of CO2. Here, we evaluate results from seismic and microgravimetric observations in addition to other available data obtained between April 2004 and July 2005, in order to shed Keywords: light on the source of these events. We discuss the information to assess whether collectively the phenomena Tenerife “ ” central complex qualify to be termed volcanic unrest , and the socio-economic implications of the phenomena, and critically fi unrest examine the ensuing scienti c response. We also evaluate the potential volcanic-eruption precursory volcano monitoring character of the data. Suggestions for the establishment of improved volcano monitoring programmes, early hazard assessment warning systems and civil response protocols for volcanic crises on Tenerife are proposed. © 2009 Elsevier B.V. All rights reserved. 1. Introduction thermal system may equally produce ground deformation and seismicity (Sturtevant et al., 1996; Bianco et al., 2004; Tikku et al., 2006; Episodes of unrest are inherent components of the lifecycle of a Gottsmann et al., 2007). As a consequence, the beginning of unrest at a volcano. In a number of recent cases including Soufrière Hills (Sparks dormant volcano presents investigators with the intrinsic dilemma as to and Young, 2002) and Mt. St. Helens (Endo et al., 1981), unrest whether the unrest will culminate in an eruptive phase, hence posing a preceded eruptions and must hence be seen as an important eruption direct threat to life and property around a volcano, or whether the precursor (Sandri et al., 2004). However, there are also examples of “unusual” behaviour will eventually dissipate, causing little disruption unrest waning-off after months or years of restlessness without any to communities and hence little socio-economic damage. This uncer- eruptive volcanic activity. Most prominent cases include the volcanic tainty is even more challenging and extends to the basic question of how calderas of Long Valley (Battaglia et al., 2003a,b) and the Campi to define unrest when the dormant volcano has not erupted in historical Flegrei (Dvorak, and Berrino, 1991). times or has not previously shown signs of unrest, either witnessed by a Volcanic unrest is the manifestation of complex sub-surface local population or recorded by a monitoring network. This situation processes leading to detectable signals at the ground surface. Processes was dramatically illustrated, for example, by the eruptions of El Chichón such as magma migration and emplacement, tectonic and hydrothermal (1982) and Popocatépetl, (1994) (México) (De La Cruz-Reyna and activity can trigger seismicity, ground deformation, thermal variations Tilling, 2007), Pinatubo (Philippines) (1991) (Newhall and Punongba- and changes in the potential fields around a volcano. Seismicity and yan, 1996), or Soufrière Hills (Montserrat) (1995–present) (Kilburn and ground deformation may be induced by brittle failure of surrounding Voight, 1998; Sparks and Young, 2002). rocks due to the pressure increase accompanying the replenishment of The Spanish volcanological community was confronted with this magma reservoirs and the exsolution of a gas phase, a process regarded dilemma in early 2004, during a period of increased seismic activity as a key trigger for volcanic eruptions (Murphy et al., 1998). and manifestations of activity that was potentially volcanic began on Alternatively, volume/pressure increases within a sub-surface hydro- the volcanic island after a quiescence of almost 100 years. The lack of both previous data and a volcano monitoring network, created a particular situation in which the available information was assessed ⁎ Corresponding author. and interpreted based on comparison to other volcanic systems, not E-mail address: [email protected] (J. Martí). necessarily to Tenerife, and on the expertise of the scientists involved 0377-0273/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jvolgeores.2009.01.028 Author's personal copy 24 J. Martí et al. / Journal of Volcanology and Geothermal Research 182 (2009) 23–33 in the investigation. However, there was no general consensus on observed phenomena by various authors with respect to the abnormal either the volcanic evolution of Tenerife or on its current state of activity on Tenerife. activity to use as a basis for judging the future outlook. This gave rise to a rather confusing situation in which some scientists defined the 2. Volcanological background information anomalous behaviour as volcanic unrest (García et al., 2006; Gottsmann et al., 2006), while others claimed that there was no The Canary Islands form a volcanic archipelago with a long-standing clear indication for unrest (Carracedo and Troll, 2006; Carracedo et al., history of volcanic activity that began more than 40 million years ago 2006). This controversy, which is in part due to the lack of knowledge (Araña and Ortiz, 1991; Anguita and Hernan, 2000). More than a dozen on the Tenerife volcanology, was particularly dramatic in the light of eruptions have occurred on the islands of Tenerife, Lanzarote, and La a possible reawakening of the Teide-Pico Viejo volcanic complex, as Palma since the 16th century. Tenerife, the largest of the Canary Islands, there is clear disagreement concerning whether or not this is still has an eruptive history of over 12 million years including a shield an active volcanic complex (Ablay and Marti, 2000; Carracedo building phase followed by the construction of a central volcanic et al., 2003; García et al., 2006; Carracedo et al., 2007; Marti et al., structure, the Las Cañadas edifice (Marti et al., 1994)(Fig. 1). The 2008). volcanic evolution of Tenerife comprises both constructive and Unfortunately, the situation experienced in Tenerife is not ex- destructive phases including vertical and lateral collapses on the order clusive to this region, but has occurred previously in other volcanic of several km3 (Marti et al., 1997). At least three vertical collapses areas (e.g., the Guadeloupe crisis in 1976, Tazieff, 1979) and it will resulted in the formation of the 16 km-wide Las Cañadas caldera, into most certainly occur again somewhere else in the future. In an attempt which the prominent Teide-Pico Viejo volcanic complex was emplaced to address the hazards and risk implications of a poorly known during predominantly effusive and also occasional explosive activity volcanic system, we analyse the particular case of Tenerife. We present over the past 170–190 ka (Marti et al., 1994; Marti and Gudmundsson, data collected prior to and (with an emphasis) during the crisis from 2000; Ablay and Marti, 2000). This complex appears to be fed by both early 2004 to late 2005 from geophysical investigations including shallow-level (b5 km) phonolitic magma reservoirs and deeper-seated seismic, gravimetric and geodetic observations, and discuss whether basaltic magma patches (Ablay et al.,1998; Ablay and Marti, 2000; Martí or not these data allow to suggest a change in the behaviour of et al., 2008). Recent (b0.5 ka) volcanic activity was located on the Teide- volcanic system on Tenerife, i.e. the occurrence of volcanic unrest. We Pico Viejo complex (explosive and effusive phonolitic eruptions) as well also discuss historic volcanic activity on Tenerife in the light of theses as along a NW–SE and NE–SW oriented extensional structural new investigations and examine whether or not Teide should still be

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