Long Term Ground Deformation in Volcanic Islands: Tenerife and La Palma, Canaries

Canary Islands form a volcanic archipelago with 7 major islands with a long-standing history of volcanic activity that began more than 40 million years ago More than a dozen eruptions have occurred on the islands of Tenerife, Lanzarote, and La Palma since the 16 th century. We used several geodetic techniques in order to achieve ground deformation on those islands. We propose that the measured deformation is directly related to gravitational sinking of the intrusive core the island into a weak lithosphere. We favour this thesis, relative to that of spreading, because neither the published data on the geology of Tenerife show evidence of compressional structures around the base of the island nor the GPS data indicate significant radial displacements, which would have been present in the case of spreading. In adition, given that the crust has been inflected under the mass of Tenerife, following Borgia (1994), we propose that the volcanic edifice is in a state of compression, which, in some volcanoes, has in the past been associated with hazardous explosive eruptions

Application of CPT, an advanced DInSAR technique, to study surface displacement near Itoiz dam, Navarra, Spain

Itoiz reservoir is located in Navarra, northern Spain, being a newly constructed gravity dam that stores the water from the Irati and the Urrobi rivers. The dam has a total height of 121 m, a total length of 525 m and a maximum water storage volume of 410 hm3. The aim of this work is to study the surface displacement field during the impoundment of the Itoiz water reservoir, Figure 1. Orbital SAR Differential Interferometry (DInSAR) techniques have been proven to be a useful and powerful tool in tectonic areas for surveying subtle surface deformations over several years related to geodynamic phenomena. An advanced DInSAR observation technique, Coherent Pixel Technique (CPT), has been applied to study the existence of deformation in the dam area in order to obtain mean velocities and time series of deformation. We have studied the applicability of this technique to study the surface displacement field during the impoundment of the Itoiz water reservoir. Specifically, we focus on the analysis of the stability of the left slope of the reservoir. See [1,2] for more details. We have used ERS and ENVISAT descending and ascending images concerning to the 1992-2008 and 2003-2008 periods respectively. We compare the observation results with the displacement induced by water loading obtained using a theoretical model.Peer reviewe

Space Geodesy, Potential Fields (gravity and geomagnetic) and Geomathematics

This new research sub-line, part of the Research Line/Department at Institute of Geosciences “Earth Dynamics and Earth Observation”, includes the activities of four previously existing research groups: (i) Space Geodesy,Gravimetry and Geomathematics, (ii) Palaeomagnetism, Rock Magnetism and Geomagnetic Modelling, (iii) Terrestrial and Planetary Magnetic Field and Aeronomy, and (iv)Gravimetry, Tides and Geodynamics. These four research groups, which are included on it to work together and cooperate during the next years, have been working until now independently and with very few cooperation between them. In short, it includes the study and modelling of the Earth’s (and others celestial bodies’) shape, gravity and magnetic fields, and their variations in time and space, using terrestrial and space integrated geodetic, gravimetric, geomagnetic and paleomagnetic data and advanced mathematical models and techniques

On the applicability of an advanced DInSAR technique near Itoiz and Yesa reservoirs, Navarra, Spain.

In this paper we show the applicability of orbital Synthetic Aperture Radar (SAR) Differential Interferometry (DInSAR) with multiple images for terrain deformation episodes monitoring. This paper is focused on the Coherent Pixels Technique (CPT). This technique has been tested with ERS SAR and ENVISAT ASAR data for the period 1992-2008 from The Itoiz and Yesa reservoirs. These ones, located in Navarra, northern Spain, are constructed gravity dams that stores the water from the Irati and the Urrobi rivers, and the Aragón river respectively. The results has been compared with theoretical results obtained using an analytical model.Peer reviewe

DInSAR, GPS and gravity observation results in La Palma, Canary islands

We review several results from geodetic observations carried out in La Palma Island during the period 1992-2007. A gravity survey was done for structural studies, and InSAR and GPS observations techniques were applied to study the existence of deformation areas in the Island. Gravity anomalies have been inverted using a non-linear three-dimensional gravity inversion approach to obtain the geometry of the anomalous bodies. The main structural feature is a large high density body interpreted as a dense intrusive plutonic body and the pliocene-age uplifted seamount. An elongated minimum is detected below the Cumbre Vieja according to the rift structure. InSAR results show two areas of subsidence, a mild long wavelength signal on the western part of Cumbre Vieja and clear subsidence located on the Teneguia volcano where the last eruption took place in 1971. A GPS network composed by 26 stations covering the island has been defined. Vertical displacements determined by comparing the GPS coordinates obtained in 2007 and in 1994 are consistent with the InSAR results. From the comparison of 2006 and 2007 coordinates we conclude that more time span is needed to obtain clearly significant displacements, but observed trends are also consistent with InSAR results. All the observed significant displacements are at stations located outside of the large high density central body.Peer reviewe

Geodetic and structural research in La Palma, Canary Islands, Spain: 1992-2007 results

We review the results of the geodetic and structural studies carried out on La Palma Island using geodetic and geophysical data during the period 1992–2007. InSAR and GPS observation techniques were applied to study the existence of deformation on the island and gravity observations were carried out for structural studies. Gravity data were inverted using a nonlinear three-dimensional gravity inversion approach to obtain the geometry of the anomalous bodies constructed in a random growth process with respect to an exponentially stratified background. The main structural feature is a large central body (under the Caldera de Taburiente) with high density, which was interpreted as the Pliocene-age uplifted seamount and a relatively dense intrusive plutonic complex/magma body. The Cumbre Vieja series is characterized by elongated minima distributed according to the rift structure. InSAR results show a clear subsidence located on the Teneguía volcano, where the last eruption took place in 1971. A thermal source is the most probable origin for this deformation. A GPS network composed of 26 stations covering the total island surface was set up. Vertical displacements determined comparing the GPS coordinates obtained in 2007 with coordinates determined in 1994 are consistent with the InSAR results obtained in the southern part of the island. This is not the case for the northern part. From the comparison of 2006 and 2007 coordinates it is clear that more time is needed to obtain significant displacements, but observed trends are also consistent with InSAR results. All the observed significant displacements are in stations located outside of the large high-density central body.Peer reviewe