Hydrothermal system of Central Tenerife Volcanic Complex, Canary Islands (Spain), inferred from self-potential measurements

doi:10.1016/j.jvolgeores.2013.12.007

Journal of Volcanology and Geothermal Research

Volume 272, 15 February 2014, Pages 59-77

https://doi.org/10.1016/j.jvolgeores.2013.12.007 Get rights and content

Highlights

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Characterization of hydrothermal systems in central Tenerife by self-potential
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Long-lived hydrothermalism exclusively over shallow felsic magma reservoirs
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Fossil hydrothermal activity at some points along Las Cañadas caldera wall
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Independent groundwater systems in Ucanca, Guajara and Diego Hernández calderas
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Diego Hernández groundwater system geometry reveals an almost closed caldera.

Abstract

An extensive self-potential survey was carried out in the central volcanic complex of Tenerife Island (Canary Islands, Spain). A total amount of ~ 237 km of profiles with 20 m spacing between measurements was completed, including radial profiles extending from the summits of Teide and Pico Viejo, and circular profiles inside and around Las Cañadas caldera and the northern slopes of Teide and Pico Viejo. One of the main results of this mapping is the detection of well-developed hydrothermal systems within the edifices of Teide and Pico Viejo, and also associated with the flank satellite M. Blanca and M. Rajada volcanoes. A strong structural control of the surface manifestation of these hydrothermal systems is deduced from the data, pointing to the subdivision of Teide and Pico Viejo hydrothermal systems in three zones: summit crater, upper and lower hydrothermal systems. Self-potential maxima related to hydrothermal activity are absent from the proximal parts of the NE and NW rift zones as well as from at least two of the mafic historical eruptions (Chinyero and Siete Fuentes), indicating that long-lived hydrothermal systems have developed exclusively over relatively shallow felsic magma reservoirs. Towards Las Cañadas caldera floor and walls, the influence of the central hydrothermal systems disappears and the self-potential signal is controlled by the topography, the distance to the water table of Las Cañadas aquifer and its geometry. Nevertheless, fossil or remanent hydrothermal activity at some points along the Caldera wall, especially around the Roques de García area, is also suggested by the data. Self-potential data indicate the existence of independent groundwater systems in the three calderas of Ucanca, Guajara and Diego Hernández, with a funnel shaped negative anomaly in the Diego Hernández caldera floor related to the subsurface topography of the caldera bottom. Two other important self-potential features are detected: positive values towards the northwestern Santiago rift, possibly due to the relatively high altitude of the water-table in this area; and a linear set of minima to the west of Pico Viejo, aligned with the northwestern rift and related to meteoric water infiltration along its fracture system.

Introduction

Persistent active subaerial volcanism is usually accompanied by hydrothermal activity, which develops an energy transfer between the deep magmatic reservoirs and the surface layers of a volcanic system. The heat exchange between these two distinct parts of a volcanic system is performed mainly by convection of subsurface fluids, both by groundwater circulation supplied by meteoric water recharge and also by the ascension of hot volcanic gasses liberated from deep magma cooling and gas exsolution during magma migration toward the surface (Giggenbach, 1996, Ingebritsen et al., 2006, Ingebritsen et al., 2010, Pirajno, 2009). Hydrothermal activity greatly enhances alteration and argillization of volcanic rocks and therefore constitutes one of the major agents in mechanical alteration of volcanic edifices (Siebert et al., 1987, Lopez and Williams, 1993, Wyk et al., 1997, Kerle et al., 2001, Reid et al., 2001, Wyk et al., 2001, Cecchi et al., 2005). Because of this, hydrothermal alteration is considered a major factor affecting volcano flank stability (Aizawa, 2008, Aizawa et al., 2009) and it is usually invoked to explain volcanic landslides and gravitational flank collapses, which are widely observed in volcanic oceanic islands (Le Friant et al., 2003, Le Friant et al., 2004, Merle and Lénat, 2003, Merle et al., 2006, Barde-Cabusson and Merle, 2007, Romagnoli et al., 2009a, Romagnoli et al., 2009b). Hydrothermal systems can develop a strong coupling with the eruptive activity of their parent magmatic systems and sometimes the state of the hydrothermal system, its spatial dimensions and the intensity of the heat transfer can be used as a volcano monitoring tool (Aubert et al., 2008, Gaudin et al., 2013). The lateral extension and the geometry of a hydrothermal system are highly variable, depending on diverse factors, both internal to the volcanic system, like structural boundaries (caldera, craters, regional faults, weakness areas) and also external, like the pattern and magnitude of meteoric groundwater recharge by rain and snow (Finizola et al., 2004, Tort and Finizola, 2005, Barde-Cabusson et al., 2012, Peltier et al., 2012).

In the present work we have focused on the central area of Tenerife Island (Canary Islands, Spain), dominated by Teide and Pico Viejo stratovolcanoes and Las Cañadas caldera, in which active hydrothermal activity is evidenced by fumaroles, thermal anomalies and CO₂ diffuse emission in Teide summit and upper-cone flanks. Several geophysical studies (gravimetric, magnetic, seismic and magnetotelluric) have been devoted to this area (Ablay and Keary, 2000, Araña et al., 2000, Canales et al., 2000, Pous et al., 2002, Coppo et al., 2008, Coppo et al., 2009, Coppo et al., 2010, Gottsmann et al., 2008, Blanco-Montenegro et al., 2011, Camacho et al., 2011) but only a few have focused on its hydrothermal system (García de la Noceda et al., 1989, Aubert and Kieffer, 1996, Ohno et al., 2004). The surface expression of Teide summit hydrothermal system has been recently studied by Del Potro et al. (2009), who analyzed also the mechanical properties of the clay-rich materials resulting from the hydrothermal alteration (alunite and kaolinite, Del Potro and Hürlimann, 2009). Although these two works provide a useful general cartography of upper-Teide hydrothermal field, no information is available about the subsurface extension and magnitude of the corresponding hydrothermal system.

Knowledge about Teide–Pico Viejo hydrothermal system can be very useful at least in two different ways. Firstly, any realistic investigation on the mechanical properties and inner strength of Teide–Pico Viejo edifices must take into account the extension, geometry and degree of hydrothermal alteration experienced by their subsurface materials, with obvious implications about the potential for future lateral collapses and about the possibility of any deformation having affected these volcanic edifices (for example volcano spreading, see Márquez et al., 2008). Secondly, it can serve to further develop volcano monitoring tools based on the observation of the state and intensity of the hydrothermal system associated to this volcanic area, either by periodic repetition of geophysical measurements in selected areas or by the installation of continuous monitoring.

The objective of our work has been to study (1) the extension, geometry and structure of the hydrothermal systems and (2) some hydrogeological main features of the Teide–Pico Viejo complex of Tenerife summit. We have chosen the self-potential method due to its sensitivity to subsurface fluid movement, which makes it an ideal tool to investigate hydrothermal activity and its interaction with structural boundaries in volcanic edifices (Corwin and Hoover, 1979, Revil and Pezard, 1998, Revil et al., 1999a, Revil et al., 1999b, Revil et al., 2004, Revil et al., 2008, Finizola et al., 2002, Finizola et al., 2003, Finizola et al., 2004, Finizola et al., 2006, Zlotnicki and Nishida, 2003, Ishido, 2004). Our results will be compared with other complementary geophysical studies already performed in the summit part of Tenerife Island.

Section snippets

Geological setting

The bulk of Tenerife Island consists of basaltic materials accumulated over the seafloor since at least the middle Miocene, forming a basaltic shield whose oldest subaerial exposures are probably older than 11.9 Ma (Abdel-Monem and Watkins, 1972, Ancochea et al., 1990, Thirwall et al., 2000, Guillou et al., 2004). The eroded remnants of this shield-building phase make up the Anaga, Teno and Roque del Conde massifs (see Fig. 1). Later, the emission of more evolved magmas (mainly basalts,

Self-potential method

There are several geophysical methods especially useful to investigate the subsurface structure of volcanic hydrothermal systems, particularly those based on the electrical properties of subsurface materials. Hydrothermal activity in heterogeneous volcanic systems produces very sharp changes in groundwater content and flow direction between different parts of the volcanic system and it also induces strong alteration and argillization of parent volcanic materials. These are primary factors

Data acquisition and processing

The self-potential mapping of the active volcanic system of central Tenerife reported in the present work constitutes by its surface extension, by the total longitude of measured profiles (237 km) and by the number of measurements (11,911 points during seven campaigns between 2007 and 2011), one of the most important efforts of this type performed until now. A spacing of 20 m between consecutive measurements was chosen to allow enough resolution to detect any linear small-scale feature like

Results and interpretation

The results of the SP mapping are shown in Fig. 3, Fig. 4, Fig. 5. Fig. 3 shows the interpolation of the data (50 m grid, see the previous paragraph for procedure). Fig. 4, Fig. 5 show the original SP measurements (20 m spacing) along 3 main profiles cutting Teide, Pico Viejo, Montaña Blanca and Montaña Rajada edifices in different directions (Fig. 4) and 3 additional profiles crossing Diego Hernández caldera (Fig. 5).

Discussion

Once the main features revealed by the SP mapping have been presented, some additional insights about their significance can be gained comparing them with the results of previously published geophysical studies.

Conclusions

The self-potential survey described in this paper has revealed the surface extension and structure of the hydrothermal system of central Tenerife. Strong hydrothermal activity has been detected in Teide and Pico Viejo edifices, while weaker hydrothermal systems, either active or fossil, are observed in Montaña Blanca and Montaña Rajada flank satellite felsic vents. SP data seem to indicate also the presence of fossil hydrothermal activity along some parts of the floor of Las Cañadas caldera

Acknowledgments

We are grateful to the Cabildo de Tenerife and the Parque Nacional del Teide for their authorization to work in this Unesco World Heritage Site. We thank the Teleférico del Teide for the support and facilities during fieldwork in the upper part of Teide and Pico Viejo edifices. We are grateful to the Parador Nacional de las Cañadas del Teide, the Observatorio Astronómico del Teide and the Observatorio Meteorológico de Izaña for their facilities and help. Thanks to Clelia and Cristina Perez from

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Such a configuration supports the accumulation of dense magma at the interior of the central part of the island, but not the hypothesis that the evolution of Tenerife involved the construction of three isolated proto-islands (Teno, Anaga and Roques del Conde), the space in between which was subsequently occupied by the central complex (Ancochea et al., 1990; Carracedo, 1994; Walter, 2003). The low-density contrast located below the Teide-Pico Viejo and Las Cañadas caldera (numbered 2 in Fig. 4) is interpreted to be the combined effect of i) low-density phonolitic materials filling the collapsed sector of the Las Cañadas edifice (Martí et al., 1994), ii) the infill of the caldera depression by poorly consolidated, highly porous and permeable lavas from Teide and Pico Viejo (Martí et al., 2008), iii) the presence of a deep aquifer inside the caldera depression (Coppo et al., 2008), iv) the existence of an active hydrothermal system (Piña-Varas et al., 2014; Villasante-Marcos et al., 2014), and v) the presence of fresh magma accumulated at shallow depths (Ablay et al., 1998; Andujar, 2007). This latter contributing factor is consistent with the results obtained by the array beam-forming method that reveals possible fractures filled by volatiles or magma at 2–4 km b.s.l. in the Las Cañadas caldera (Barros et al., 2012).
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2019, Earth-Science Reviews
Citation Excerpt :
As it was mentioned for the existing physical volcanology data, geophysical data have not been considered in any of the works that support an origin of the caldera by sector collapse. However, geophysical studies, including magnetism, gravimetry, magnetotellurics, audio-magnetotellurics, seismic tomography, and self-potential studies, provide structural data on the interior of Tenerife that are crucial to interpret the internal structure of the Las Cañadas caldera and consequently, its origin (see MacFarlane and Ridley, 1968; Vieira et al., 1986; Ortiz et al., 1986; Camacho et al., 1991, 2011; García et al., 1997; Aubert and Kieffer, 1998; Ablay and Kearey, 2000; Araña et al., 2000; Almendros et al., 2000, 2007; Pous et al., 2002; Gottsmann et al., 2008; Coppo et al., 2008, 2010; García-Yeguas, 2010; Blanco-Montenegro et al., 2011; De Barros et al., 2012; García-Yeguas et al., 2012, 2017; Prudencio et al., 2013, 2015; Piña-Varas et al., 2014, 2015; Villasante-Marcos et al., 2014). Summarising the main findings among all these studies, the following observations arise (Fig. 15): 1) the existence of important negative gravimetric anomalies in the interior of Las Cañadas caldera; 2) the presence of low magnetic materials infilling the caldera depression and high magnetic anomalies along the rift systems; 3) the existence of a conductive level below the post-caldera infill, the topographic surface of which reveals the presence of several depressions, corresponding to the western (Ucanca), central (Guajara), and eastern (Diego Hernández) zones, outlined by Martí et al. (1994); 4) the presence of hydrothermal alteration along the entire boundary of the caldera, even below the TPV complex; 5) the presence of the structural wall of the Las Roques de García rooted at depth separating the depressions of Ucanca and Guajara; and 6) the existence of a structural discontinuity between the interior of the caldera and the Icod valley, marked by a sharp contrast in electrical conductivity, density, and with strong seismic wave refractions (Almendros et al., 2007).
The Las Cañadas caldera is one of the best exposed volcanic calderas in the world and one of the few known evolved alkaline volcanoes. It truncates the pre-Teide-Pico Viejo central volcanic edifice, the Las Cañadas edifice, which started to take shape at the end of the formation of a large basaltic shield that forms the main part of island of Tenerife. Historically, the origin of the Las Cañadas caldera has been controversial, as it has been interpreted as the result of either multiple vertical collapses or due to a giant sector collapse. The available stratigraphical, structural, volcanological, geochronological, and geophysical data, as well as its comparison to other well-known collapse calderas should not offer any doubt as to its direct relationship with a long history of phonolitic explosive volcanism. However, the existence of large landslide events on Tenerife, which have significantly modified the flanks of the Las Cañadas volcano, have also been used as a potential explanation for the origin of the Las Cañadas depression. This contribution reviews the available information on the Las Cañadas caldera, the causes of this controversy, and rationalises the most plausible explanation for the origin of Las Cañadas caldera based on the current evidence gathered from all previous studies.

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