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Blanco, I.
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Blanco, I.
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- PublicationOpen AccessMagnetic study of the Furnas caldera (Azores)(1997-03)
; ; ; ;Blanco, I.; Departamento de Volcanología, Museo Nacional de Ciencias Naturales, CSIC, Madrid, Spain ;Garcìa, A.; Departamento de Volcanología, Museo Nacional de Ciencias Naturales, CSIC, Madrid, Spain ;Torta, J. M.; Departamento de Volcanología, Museo Nacional de Ciencias Naturales, CSIC, Madrid, Spain; ; A local ground magnetic study of the Furnas caldera (S. Miguel Island, Azores) has provided new insight into the magnetic structure of this volcano. Analysis of the data comprised removal of the IGRF, reduction to the pole, pseudogravity integration and upward continuation. Also, a spectral method was applied to estimate the depth to the magnetic sources, as well as a 2.5D forward modelling technique. Magnetic properties obtained at the laboratory for some representative sample rocks were considered in the modelling process. The most relevant features are the existence of an important negative anomaly inside the caldera and of an intense positive anomaly to the south of the coast. The former points out a decrease in the magnetization of the caldera filling materials with respect to the surrounding rocks, which could be explained as the result of post-eruption processes such as hydrothermal alteration. This is expected as Furnas has an active hydrothermal system probably related with a magmatic reservoir at high temperature. The positive anomaly suggests the existence of a strongly-magnetized body beneath the south coast.271 766 - PublicationOpen AccessHigh-resolution aeromagnetic survey of the Teide volcano (Canary Islands): a preliminary analysis(1997-03)
; ; ; ; ;Garcìa, A.; Departamento de Volcanología, Museo Nacional de Ciencias Naturales, CSIC, Madrid, Spain ;Blanco, I.; Instituto Geográfico Nacional, Madrid, Spain ;Torta, J. M.; Departamento de Volcanología, Museo Nacional de Ciencias Naturales, CSIC, Madrid, Spain ;Socías, I.; Instituto Geográfico Nacional, Madrid, Spain; ; ; To contribute to our understanding of the structure of the Teide volcano, a detailed aeromagnetic survey was carried out covering the area of Las Cañadas caldera and the Teide-Pico Viejo complex. Taking into account the rugged relief of the area (altitude ranges from sea level to almost 4000 m), a terrain correction has been applied. As a first approximation, the topography has been characterized by a uniform magnetization of 5 Am-1 (based on field and laboratory rock magnetic data). Several enhancement techniques have been applied to the residual map (original map minus topographic effect), such as reduction to the pole, pseudogravity integration and upward continuation. In the reduced-to-the-pole map the large positive anomaly that appears centered to the north of Pico Viejo is noteworthy and could be caused by a basaltic intrusion responsible for the last eruptions in this area. Also, a small magnetic low appears over Teide peak, which should be related to slightly-magnetized shallow phonolitic materials. The main tectonic direction of Tenerife, SW-NE, is also clearly reflected on the magnetic anomaly map. The comparison between the pseudogravity and the Bouguer anomaly maps indicates a good correlation between magnetic and gravimetric sources.244 698 - PublicationOpen AccessA search for the volcanomagnetic signal at Deception volcano (South Shetland I., Antarctica)(1997-03)
; ; ; ; ; ; ;Garcìa, A.; Departamento de Volcanología, Museo Nacional de Ciencias Naturales, CSIC, Madrid, Spain ;Blanco, I.; Departamento de Volcanología, Museo Nacional de Ciencias Naturales, CSIC, Madrid, Spain ;Torta, J. M.; Departamento de Volcanología, Museo Nacional de Ciencias Naturales, CSIC, Madrid, Spain ;Astiz, M. M.; E.T.S. Arquitectura, Universidad Politécnica de Madrid, Spain ;Ibáñez, J. M.; Instituto Andaluz de Geofísica, Granada, Spain ;Ortiz, R.; Departamento de Volcanología, Museo Nacional de Ciencias Naturales, CSIC, Madrid, Spain; ; ; ; ; After the increase in seismic activity detected during the 1991-1992 summer survey at Deception Island, the continuous measurement of total magnetic intensity was included among the different techniques used to monitor this active volcano. The Polish geomagnetic observatory Arctowski, located on King George Island, served as a reference station, and changes in the differences between the daily mean values at both stations were interpreted as indicators of volcanomagnetic effects at Deception. A magnetic station in continuous recording mode was also installed during the 1993-1994 and 1994-1995 surveys. During the latter, a second magnetometer was deployed on Deception Island, and a third one in the vicinity of the Spanish Antarctic Station on Livingston Island (at a distance of 35 km) and was used as a reference station. The results from the first survey suggest that a small magma injection, responsible for the seismic re-activation, could produce a volcanomagnetic effect, detected as a slight change in the difference between Deception and Arctowski. On the other hand, a long term variation starting at that moment seems to indicate a thermomagnetic effect. However the short register period of only two stations do not allow the sources to be modelled. The future deployment of a magnetic array during the austral summer surveys, throughout the volcano, and of a permanent geomagnetic observatory at Livingston I. is aimed at further observations of magnetic transients of volcanic origin at Deception Island.234 203