![]() The objective of the present study was to monitor Turrialba volcano, analyzing hydrothermal alteration on three dates within the period 1986-2003 and relating results with observed volcanic activity. Hematite and goethite (iron oxides) have strong absorptions in UV region affecting the nearby visible, mainly the range of 450 and 520 nm. This feature is related to charge transfer absorptions caused by the movement of electrons between ferrous and ferric states due to a photon interaction (Clark 1995). On the other hand, the distinctive absorption feature of iron oxides appears in the visible region of electromagnetic spectrum. This distinctive feature occurs always in the SWIR region at 2210 nm, characteristic of clays, allowing for clay identification. The diagnostic absorption feature of clays results from a combination of vibrational processes, specifically Al-OH bending plus OH stretching (Clark 1995). 2005 and Pekesin 2005), selecting those input bands which are equivalent to Thematic Mapper (TM) bands. ![]() This methodology has been successfully implemented in ASTER data (Crosta et al. 2005) and tropical areas (Ruiz-Armenta & Prol-Ledesma 1995 Torres et al.1998 Suarez 2003). 2003, Delendatti 2003 Yetkin 2003, Ducart et al. 2003 Suarez 2003) in several scenarios, such as low vegetated areas (Crosta et al. It has been widely used for hydrothermal alteration delineation (Torres et al.1998 Mhalanga 2002 Mohammadzadeh & Babaee 2006 Crosta et al. This methodology was based on a series of Principal Component (PC) transformations over Thematic Mapper bands. ![]() Clays and iron oxides are the target materials for detection using Crosta Technique (Crosta and Mc Moore, 1989 Loughlin, 1991). Hydrothermal alteration is an indicator of volcanic activity, as it results from the interaction between minerals and thermal fluids, normally of volcanic origin. Palabras clave: Monitoreo volcánico, alteración hidrotermal, análisis de componentes principales, teledetección, volcán Turrialba, Costa Rica Esta investigación contribuye al establecimiento de sistemas de monitorización de volcanes basados en teledetección. Las recientes erupciones freáticas se han producido en las mismas zonas, validando los resultados. El análisis multitemporal mostró un claro incremento en las áreas de alteración entre 1986 y 2003 en los cráteres central y SW. El graben del complejo fue delimitado adecuadamente mostrando alteraciones tanto limoníticas como argílicas en una alineación N-S. Los resultados son consistentes con la actividad volcánica entre 1986 y 2003, en la que la actividad se concentró en los cráteres central y SW. Se elaboraron mapas de arcillas y óxidos de hierro para 1986, 2001 y 2003. Esta técnica se adaptó al sensor MASTER, seleccionando las bandas relevantes para la detección de minerales. Los análisis se realizaron empleando cuatro bandas como dato de entrada de análisis de componentes principales (ACP) para detectar mineralogías (arcillas y óxidos de hierro). Para ello se analizaron diferentes imágenes en fechas diferentes, Thematic Mapper (1986 y 2001) e imágenes aeroportadas MODIS/ASTER (2003). Keywords: Volcano monitoring, hydrothermal alteration, PCA, remote sensing, Turrialba volcano, Costa Rica.Įn este trabajo se analiza la alteración hidrotermal en el volcán Turrialba, sistema activo de la Cordillera Volcánica Central de Costa Rica. This research contributes to the establishment of monitoring systems in volcanic areas based on remote sensing. Reactivation of phreatic activity since 2010 developed in the same areas where increasing alteration was detected, thus validating results. Multitemporal analysis showed enlargement of alteration area in Central and Southwestern craters. Graben area was characterized by an overlap of alterations (limonitic and argillized) along an N-S alignment. Image analysis results are consistent with volcanic activity from 1986 to 2003. Argillic and limonitic zones were mapped for 1986, 20 images. ![]() The technique was adapted to MASTER sensor, selecting relevant bands for mineral detection. Analyses were carried out using 4 input bands in PCA transformations to detect clays and iron oxides. Principal component analysis (PCA) techniques were applied to Thematic Mapper (19) and MODIS/ASTER airborne imagery (2003). Hydrothermal alteration was analyzed in the active Turrialba Volcano, Central Volcanic Range, Costa Rica. Rejas 3 *, Javier Bonatti 4 *, Jesús Martínez-Frías 5 * & Rubén Martínez 6 * Esperanza Bragado-Massa 1 *, Miguel Marchamalo 2 *, Juan G.
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