A qualitative and quantitative analysis of 13 Landsat TM and ETM+ images of Lascar volcano for the 2000-2004 period was performed by applying the three bands and three components method to determine heat and mass flux and understand the magma circulation process in a passive degassing volcano related to permanent fumarolic activity. The behavior and evolution of spectral radiance during the study period suggest that prior to low-to-moderate magnitude eruptions these values reach their localized temporal minimum levels, corresponding to 1.9-4.38 mW/cm(2)sr mu m in July 2000 and 4.38-7.11 mW/cm(2)sr mu m in December 2003 eruptions, respectively. Similar behavior is observed for anomaly area, heat and mass fluxes. During the 2000-2004 period the heat flux was estimated to vary from 75.46 and 10,527 MW, while mass flux ranged between 131 and 18,469 kg s(-1). A magma circulation model is proposed to explain these variations, where the thermal anomaly is related to the presence of a fumarolic field and fluids movement from a magma chamber located at similar to 10-17 km depth. (C) 2015 Elsevier B.V. All rights reserved.