ANALYSIS OF BASALTIC LAVA FLOWS AT CERRO NEGRO VOLCANO, NICARAGUA USING SPACEBORNE TIR DATA

Cerro Negro, located in northwestern Nicaragua, is a 250 m tall basaltic volcano that exhibits strombolian to subplinian explosions and occasional effusive activity. Since its formation in 1850, Cerro Negro has erupted more than 20 times, producing multiple a’a lava flows. The six flows extend in a complicated pattern, up to 6 km to the north-northeast. This investigation attempts to relatively date these flows and determine their mineralogy using remote and in-situ thermal infrared (TIR) spectroscopic techniques. Results demonstrate that data from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) of the relatively-recent basalts correlate well with changes observed in the laboratory data, and those reported in previous studies of Hawaii. A compositional deconvolution analysis of both emissivity datasets was used to create mineralogical end-member maps and relatively-date the young lava flows based upon their spectral signatures. ASTER-derived estimates of weathering rates indicate that iron oxide constituents of the flows chemically weather to hematite on the surface at a rate of 9 - 20%, whereas the devitrification and/or spalling of glass occurs at a slower rate of 1 - 9% over 76 years. A new thermal deconvolution algorithm was also tested for its applicability to low-temperature thermal features (fumaroles), using the ASTER shortwave infrared (SWIR) simultaneously with TIR data. The thermally mixed pixels were successfully identified based upon their elevated temperature, and degree of distortion in their emissivity spectra. Although constraining ages of flows emplaced very close in time remains a challenge using spaceborne multispectral TIR data, we have shown that it can be done and is an efficient way to map and relatively date young basaltic lava flows. The results of the lava flow compositional evolution in conjunction with future thermal studies of the fumarole field dynamics could provide insight into the future activity and the associated hazards of Cerro Negro.