USING REMOTE SENSING TO DETERMINE THE ENVIRONMENTAL IMPACT OF VOLCANIC EXTRUSIVE PRODUCTS AT ARENAL VOLCANO AND POAS VOLCANO, COSTA RICA

The investigation of possible environmental impact by volcanic extrusive products including lava, pyroclastic flows, ash fall, vent gas and diffuse gas emissions of CO₂ and SO₂ at two volcanoes in Costa Rica is the subject of this research. Evaluation of potential impact was conducted using field observations and the computerized processing of remotely sensed imagery. Processing methods included the use of true and false color composite images, contrast stretch enhancement, principal components analysis (PCA) and density slicing.

Field observations and previous investigations indicate that environmental impact at Arenal is mainly due to lava and pyroclastics while at Poas the main impact is acid deposition from efflux of SO₂. Interpretation of processed 1986 Landsat Thematic Mapper (TM) data has enabled delineation of the impact zones at both volcanoes. The impact areas are most evident in several of the visible and infrared TM bands. The area of acid deposition and vegetation kill at Poas is best indicated on the PC 2 band of the TM data. Delineation of pre-1986 flows from Arenal is possible using TM Bands 1-4 and can be compared to 2003 MODIS/ASTER Airborne Simulator (MASTER) images to differentiate the more recent impact from flows. An apparent pyroclastic event emanating from Arenal at the time the TM dataset was acquired is clearly displayed in false color composite using TM Bands 4, 5 and 7. The MASTER images also display evidence of a pyroclastic event occurring on March 21, 2003. Probable gas plumes projecting from the Arenal vent to the west are evident on several TM Bands and on the MASTER images obtained in 1986 and 2003, respectively.