Hydrothermal alteration was analyzed in the active Turrialba Volcano, Central Volcanic Range, Costa Rica. Principal component analysis (PCA) techniques were applied to Thematic Mapper (1986 and 2001) and MODIS/ASTER airborne imagery (2003). Analyses were carried out using 4 input bands in PCA transformations to detect clays and iron oxides. The technique was adapted to MASTER sensor, selecting relevant bands for mineral detection. Argillic and limonitic zones were mapped for 1986, 2001 and 2003 images. Image analysis results are consistent with volcanic activity from 1986 to 2003. Graben area was characterized by an overlap of alterations (limonitic and argillized) along an N-S alignment. Multitemporal analysis showed enlargement of alteration area in Central and Southwestern craters. Reactivation of phreatic activity since 2010 developed in the same areas where increasing alteration was detected, thus validating results. This research contributes to the establishment of monitoring systems in volcanic areas based on remote sensing.