USING OPTICAL IMAGERY DATA FOR LITHOLOGICAL MAPPING OF COMPOSITE VOLCANOES IN HIGH ARID PUNA PLATEAU. TUZGLE VOLCANO CASE STUDY;
USING OPTICAL IMAGERY DATA FOR LITHOLOGICAL MAPPING OF COMPOSITE VOLCANOES IN HIGH ARID PUNA PLATEAU. TUZGLE VOLCANO CASE STUDY

Remote sensing data are particularly suitable for the geological mapping of inaccessible and/or large non-vegetated areas. Volcanic mapping in the Altiplano-Puna plateau of the Central Andes is a challenging task due to inaccessibility, extreme climatic conditions, high altitude above sea level and dangerous issues like minefields. In this paper we present a practical spectral mapping methodology for arid volcanic regions using optical imagery data, which it has been tested in the area of the Cerro Tuzgle volcano, a Quaternary composite volcano, because of its well-known stratigraphy. Some of the most common and well known processing techniques were used to multispectral data (Landsat 7 ETM+, Landsat 8 and ASTER). Then, supervised classification and an assessment of the classification were produced for every image created. The quantitative accuracy of the classification maps resulting from different data sets was assessed by comparing the classification with ground truth data (reference data) extracted from the geological map by means of a confusion matrix and related statistics. We found that supervised classification over Principal Component Analysis images was the best methodology for lithological mapping. Low costs, data availability and broad swath of the multispectral data make these images valuable for lithological mapping in arid regions. Even if this methodology is effective to composite volcano preliminary mapping, the correct reconstruction of the stratigraphy of a volcano always requires field survey. 

Geological mapping of volcanic areas is important to unravel the evolution of the volcanism with important implication for the assessment of the geologic hazard and the exploration and exploitation of energy and mineral resources. Volcanic mapping in -Puna plateau is a challenging task due to inaccessibility, extreme climatic conditions, high altitude above sea level and dangerous issues like minefields, so an effective and validated methodology for mapping is fundamental to ensure the quality of the final results for the end-users. A practical mapping methodology using optical imagery data tested in Cerro Tuzgle because of its well-known stratigraphy is presented. Some of the most common and well known processing techniques (false color combinations, band ratios and principal component analysis) were used to multispectral data (Landsat 7, Landsat 8 and ASTER). Then, supervised classification and an assessment of the classification were produced for every image created. The quantitative accuracy of the classification maps resulting from different data sets was assessed by comparing the classification with ground truth data extracted from the geological map by means of a confusion matrix and related statistics. Since the validation over several processing techniques, we found that supervised classification over PCA in multispectral data was the best methodology for lithological mapping in volcanic areas. Comparing the three multispectral sensors used in this work, we achieve better results and more accuracy with ASTER images. Low costs, data availability and broad swath of the multispectral data make these images valuable for lithological mapping in arid volcanic regions. This time- and cost-effective methodology is adequate to composite volcano preliminary mapping, but the correct reconstruction of the stratigraphy of a volcano always requires field survey.