Remote sensing of the 1998 mudflow at Casita volcano, Nicaragua

Abstract

A devastating lahar (volcanic mudflow) occurred at Casita volcano (Nicaragua) in 1998, triggered by excessive precipitation associated with Hurricane Mitch. We investigate here the morphology and drainage structure of the flow deposition area, primarily using satellite optical and radar imagery. Because the lahar destroyed several towns and villages, killing over 2500 people, we also assess the utility of images available at the time of the event for disaster management. We find that SPOT multispectral data are most suited to delineate and characterize the flow field, but show limitations for damage assessment, and problems with cloud contamination. ERS Synthetic Aperture Radar (SAR) imagery largely failed to detect the lahar deposits, with RADARSAT performing slightly better. The relatively coarse-grained deposits, together with a dense cover of wooden debris, made the flow nearly imperceptible to the short wavelength C-Band radar, especially at ERS's steep incident angle. Because of spatial, spectral and radiometric limitations in all types of imagery used, the synergistic potential of optical and radar, as well as high- and low-resolution optical data was explored. The best synergy was found not in merged imagery, but in the incorporation of auxiliary information, such as elevation, map and GIS data. Given the cloud problem, forthcoming radar satellites with variable polarization and incident angles are expected to provide better results in comparable, future situations.