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Comunicación presntada a la 3ª Asamblea Hispano-Portuguesa de Geodesia y Geofísica = 3ª Assembleia Luso-Espanhola de Geodesia e Geofisica, celebrada en Valencia entre el 4 y el 8 de febrero de 2002. The Institute of Astronomy and Geodesy (UCM-CSIC) has installed a GPS permanent station in the geodynamic complex of Jameos in Lanzarote. In this same place there are two automated tide gauges of precision (pressure sensors). With these instruments it is sought to study the sea level variations and their possible correlation with the GPS observations. For these studies it is absolutely necessary to have an altimetric link with high accuracy between the reference point of the pillar where the GPS antenna is installed and the tide gauges bench marks. We have carried out two observation campaigns in the years 2000 and 2001. Methods of repeated geometric levelling of very short tracts have been used due to the great existent level difference. The reciprocal and simultaneous trigonometric levelling has also been used that is adapted in this type of visual inclined. In this paper the works carried out in the two epochs with the putpose of making the altimetric connections before mentioned are described. The results obtained, the evaluation of the levelling campaigns, and the comparison of the levels of different measurements are also presented.

Comunicación presntada a la 3ª Asamblea Hispano-Portuguesa de Geodesia y Geofísica = 3ª Assembleia Luso-Espanhola de Geodesia e Geofisica, celebrada en Valencia entre el 4 y el 8 de febrero de 2002., The cooperation between the 1nstitute ofAstronomy and Geodesy (CSIC-UCM) and the 1nstitute of Seismology of Wuhan (CSB) began in 1988 to develop technology and software for tidal and geodynamic investigation and applications in the field of engineering. The Geodynamics Laboratory of Lanzarote (LGL) pro vides excellent opportunities for the scientific community to test and lo check sensors and data acquisition systems developed under real conditions of observation. The first set of water tube and extensometer was installed in the observation module of Cueva de los Verdes of the LGL eight years ago. Then, differents geophysical sensors and programs for data analysis have been developed for the monitoring of the geodynamic activity in Lanzarote. We present here a review of the collaboration, with special interest in describing of the instruments. The most relevant results obtained up to now are briejly introduced.

Comunicación presntada a la 3ª Asamblea Hispano-Portuguesa de Geodesia y Geofísica = 3ª Assembleia Luso-Espanhola de Geodesia e Geofisica, celebrada en Valencia entre el 4 y el 8 de febrero de 2002., The Institute of Astronomy and Geodesy (UCM-CSIC) has installed a GPS permanent station in the geodynamic complex of Jameos in Lanzarote. In this same place there are two automated tide gauges of precision (pressure sensors). With these instruments it is sought to study the sea level variations and their possible correlation with the GPS observations. For these studies it is absolutely necessary to have an altimetric link with high accuracy between the reference point of the pillar where the GPS antenna is installed and the tide gauges bench marks. We have carried out two observation campaigns in the years 2000 and 2001. Methods of repeated geometric levelling of very short tracts have been used due to the great existent level difference. The reciprocal and simultaneous trigonometric levelling has also been used that is adapted in this type of visual inclined. In this paper the works carried out in the two epochs with the putpose of making the altimetric connections before mentioned are described. The results obtained, the evaluation of the levelling campaigns, and the comparison of the levels of different measurements are also presented.

Comunicación presntada a la 3ª Asamblea Hispano-Portuguesa de Geodesia y Geofísica = 3ª Assembleia Luso-Espanhola de Geodesia e Geofisica, celebrada en Valencia entre el 4 y el 8 de febrero de 2002., The observation's module for continuous recording of sea level variations in the LGL is located in the intersection between the volcanic tunnel of La Corona volcano and the Atlantic Ocean, at the north of Lanzarote Island in a place named Jameos del Agua. The situation and features of this module, they make of it a place of excellent characteristics to study the possible variations of sea level, which is one of the indicative parameters of a possible global climatic change. Since 1987 we have settled various tidal sensors in the most three important lakes, constituted inside the volcanic tube, in the nearby of the coast when the volcanic tube descends below ocean level. Likewise, we settled in the exterior a sea-bottom maregraph in the closest area to the coast of the Jameos del Agua. Three years ago the station was accomplished with a geodetic GPS in continuous operation, to control possible deformations of geodynamic character. Some interesting results obtained up to now are presented here, as well as the plans foreseen for the future in this module of the LGL.

Comunicación presntada a la 3ª Asamblea Hispano-Portuguesa de Geodesia y Geofísica = 3ª Assembleia Luso-Espanhola de Geodesia e Geofisica, celebrada en Valencia entre el 4 y el 8 de febrero de 2002., GPS techniques have demonstrated their usefulness in monitoring and detecting deformations, but a low cost-maximum gain technique such as InSAR must be found in order to assure the full surveillance of certain areas of interest. Two deformation areas have been detected using InSAR and two GPS geodetic campaigns have been designed to check these assessments. In this presentation we describe the results of two GPS campaigns conducted one year apart in Tenerife, Canary lslands, and designed to detect vertical movement. The results of these campaigns will provide future considerations about time span, number of points and general observation and documentation issues in order to obtain reliable results. We also describe in detail how the observation methodology and instrumentation were designed to avoid systematic errors in height and assure the necessary quality of the data.

Comunicación presntada a la 3ª Asamblea Hispano-Portuguesa de Geodesia y Geofísica = 3ª Assembleia Luso-Espanhola de Geodesia e Geofisica, celebrada en Valencia entre el 4 y el 8 de febrero de 2002., The Institute of Astronomy and Geodesy (CSIC-UCM) has installed a GPS permanent station in the geodynamic laboratory of Lanzarote, Canary Island. Starting from continuous GPS observations for four weeks some provisional coordinates of the antenna have been determined. Diverse reference systems have been used and different configurations have been rehearsed. In order to process the series of observations the software AOSS V.1.6 and Bernese V.4.2 have been used. IGS and EUREF reference stations have been used in diverse configurations. The results have been transformed to the same ITRF system. The diverse obtained solutions don't coincide, there are discrepancies that are not small in some cases. In this work the methodology and the obtained results are presented and an analysis of the same ones is done.

Comunicación presntada a la 3ª Asamblea Hispano-Portuguesa de Geodesia y Geofísica = 3ª Assembleia Luso-Espanhola de Geodesia e Geofisica, celebrada en Valencia entre el 4 y el 8 de febrero de 2002., To define the most suitable volcano monitoring system is a particularly difficu/t task in the absence of recent activity. It must take into account not only the technical optimization of the monitoring systems, but also their economic and scientific profitability. Traditionally, observations of seismic, hydrologic, or fumarolic activity have proven useful. Since volcanic activity almost inevitably produces deformation and gravity changes before, during, between and after the events geodetic techniques are now included, in the light of the lA VCEJ's recommendations regarding routine monitoring. They are proving to be a powerful tool in the monitoring of volcanic activity detecting anomalies somefimes months or weeks before the magma jlow leads to earthquakes or other eruption precursors. Geodetic monitoring thus complements seismic monitoring by extending the study of volcanic phenomena from seconds to years and providing details on the growth of magma bodies within the volcano. Canary Islands, with a population of about 1.8 mil/ion people, are located less than /00 km from the African continent. They were formed on the continental rise and slope as independent structures. Despite being on a passive margin, they are a volcanic archipelago with a long-standing history of volcanic activity that began more than 40 m.y. ago. At least a dozen eruptions occurred on the islands ofLanzarote, Tenerife, and La Palma between /500 and 197 J. Several different types of volcanic manifestations, which follow a time pattern are to be seen on the Canary Islands. This is a typical case in which the volcanic monitoring system must be carefully designed. The system must be efficient, but must also make full use of existing facilities and have acceptable installation and running costs, in line with the current inactivity. In this presentation we described a proposal for the geodetic monitoring system in Canary lslands. This monitoring system has been develoloped with base on experimental results from different research projects and the application of theoretical analysis. This system makes used of terrestrial and space geodetic techniques.

Comunicación presntada a la 3ª Asamblea Hispano-Portuguesa de Geodesia y Geofísica = 3ª Assembleia Luso-Espanhola de Geodesia e Geofisica, celebrada en Valencia entre el 4 y el 8 de febrero de 2002., Since 1995 two short base-length horizontal pendulums are continuously recording at the station Cueva de los Verdes (Geodynamics laboratory of Lanzarote). Both tilt-meters are modified from the classical Ostrovsky pendulums and are adapted to the local features of the station. The tilt-meters have a working range of measurements of +-20seconds of arc and can resolve up to one second of arc. Such technical properties allow determining the precise tilt response to Earth tides. The tidal tilt models obtained show an important influence from ocean tides. Thus, the estimated amplitude for the main harmonic constituents is of some 4-5 times larger than values measured at continental stations. In this work, the ocean loading and attraction effect, which are computed from global ocean tidal models supplemented with precise regional and local ones will be evaluated. Hence, tidal tilt observations can be corrected from this effect.

Comunicación presntada a la 3ª Asamblea Hispano-Portuguesa de Geodesia y Geofísica = 3ª Assembleia Luso-Espanhola de Geodesia e Geofisica, celebrada en Valencia entre el 4 y el 8 de febrero de 2002. The observation's module for continuous recording of sea level variations in the LGL is located in the intersection between the volcanic tunnel of La Corona volcano and the Atlantic Ocean, at the north of Lanzarote Island in a place named Jameos del Agua. The situation and features of this module, they make of it a place of excellent characteristics to study the possible variations of sea level, which is one of the indicative parameters of a possible global climatic change. Since 1987 we have settled various tidal sensors in the most three important lakes, constituted inside the volcanic tube, in the nearby of the coast when the volcanic tube descends below ocean level. Likewise, we settled in the exterior a sea-bottom maregraph in the closest area to the coast of the Jameos del Agua. Three years ago the station was accomplished with a geodetic GPS in continuous operation, to control possible deformations of geodynamic character. Some interesting results obtained up to now are presented here, as well as the plans foreseen for the future in this module of the LGL.

Comunicación presntada a la 3ª Asamblea Hispano-Portuguesa de Geodesia y Geofísica = 3ª Assembleia Luso-Espanhola de Geodesia e Geofisica, celebrada en Valencia entre el 4 y el 8 de febrero de 2002., Observations of seismic, hydrologic or fumarolic activity have proven useful as reliable eruption precursors. In the last years, geodetic measurements are being used more extensively in active volcanoes because they have been shown to provide a reliable eruption precursor. Furthermore, ground deformation measurement techniques are attracting more attention, in particular with regard to pre-eruption ground displacement. The introduction of new geodetic techniques such as Global Positioning System (GPS) and Synthetic Aperture Radar Interferometry (SAR) can be highly useful in this context, because both techniques have pro ven to be a suitable tool for ground deformation monitoring of active volcanic areas. In this frame, it is possible to demonstrate the feas ibility of using space technologies for operational decision support demonstration at a volcanic risk scenario like Canary Islands. Particularly, the good existing coherence of volcanic areas makes them very proper for InSAR techniques application. By other hand, the theoretical and observational results of the analysis of sensibility of existing classical networks have made necessary the designing and observation of a GPS network in the island of Tenerife with a global coverage and monitoring purposes. This GPS network would be a complement and checking of InSAR observations performed in the island. The main objective of this job is defining and checking the applicability of a new geodetic monitoring system in Tenerife. In order to gel this, we make use of the existing facilities in the island and the new geodetic space techniques. We try to gel the possibility of detection of deformation at any part of the island. Therefore, the new system must be able to allow us the monitoring of any existing ground movement in the island.

Comunicación presntada a la 3ª Asamblea Hispano-Portuguesa de Geodesia y Geofísica = 3ª Assembleia Luso-Espanhola de Geodesia e Geofisica, celebrada en Valencia entre el 4 y el 8 de febrero de 2002. Since 1995 two short base-length horizontal pendulums are continuously recording at the station Cueva de los Verdes (Geodynamics laboratory of Lanzarote). Both tilt-meters are modified from the classical Ostrovsky pendulums and are adapted to the local features of the station. The tilt-meters have a working range of measurements of +-20seconds of arc and can resolve up to one second of arc. Such technical properties allow determining the precise tilt response to Earth tides. The tidal tilt models obtained show an important influence from ocean tides. Thus, the estimated amplitude for the main harmonic constituents is of some 4-5 times larger than values measured at continental stations. In this work, the ocean loading and attraction effect, which are computed from global ocean tidal models supplemented with precise regional and local ones will be evaluated. Hence, tidal tilt observations can be corrected from this effect.

Comunicación presntada a la 3ª Asamblea Hispano-Portuguesa de Geodesia y Geofísica = 3ª Assembleia Luso-Espanhola de Geodesia e Geofisica, celebrada en Valencia entre el 4 y el 8 de febrero de 2002., The strain response of the Earth to tidal forces is observed in the Geodynamics Laboratory of Lanzarote Island. The instruments, installed in a gallery inside the lava tunnel of Cueva de los Verdes, are kind of horizontal ceramic-tube extensometers. Their base fines comprise from 8 to 38 m length and are orientated in two orthogonal directions (45º.2 N Y 135°.2 N), which depend on the situation in the gallery. The reliability of this instruments, which measure the variation of distance between two fixed points with a resolution of 10 -10, allow us to dispose long term series of tidal strains since 1992. The data series are analysed in order to study the stability of the instruments. Also, with these data we can determine the tidal strain models, as well as the tidal deformation and the long-term variations of strains in this island. Due to the dependence of the local conditions of the station, which is located in an island, the oceanic influence will be investigated together with local atmospheric disturbing effects. These effects are carefully studied for this station, in order to allow the identification and, if possible, its separation from other signals of interest, given the volcanic feature of the island.