Retreat of Tropical Glaciers in Colombia and Venezuela from 1984 to 2004 as Measured from ASTER and Landsat Images

Like glaciers throughout the world, tropical glaciers in the northern Andes have retreated during the last century. In this study, the retreat of Andean glaciers in Colombian and Venezuela has been mapped from Landsat and ASTER images acquired between 1984 and 2004. Glacier retreat has been mapped for three glaciated regions in Columbia, the Sierra Nevada de Santa Marta, the Sierra Nevada del Cocuy, and the Ruiz-Tolima Massif as has the retreat of the single remaining glacier on the Pico Bonpland Massif in Venezuela. From the Landsat archives, several satellite images spanning the Landsat record were selected based on cloud cover over the glaciers and which provided adequate temporal coverage. All selected satellite images of the study sites were coregistered to each other with a root mean square (RMS) error for the ground control points of less than 20 meters. Snow and ice extent in each image was classified using the Normalized Difference Snow Index (NDSI) method and a density slice was used to create a binary snow/ice map. The total glaciated area on each individual peak was then determined from the classified snow and ice areas. This approach was found to be effective in determining glacier area. Incorporating historical data, a time series of glacier retreat from the early 1950s to 2003 was established. All four studied regions studied showed glacier retreat over this period. In the 1950s, the overall area of glaciers studied in Colombia and Venezuela glaciers was 91.36 km in the 1950s. By 2003, the glaciers had retreated to approximately 62.07 km which represents a total ice loss of 32%.