Elevation changes of Alamkouh glacier in Iran since 1955, based on remote sensing data

Abstract

To reconstruct morphometric changes in alpine glaciers, accurate and repeatable topographic surveys are required. In the present study, the elevation changes of Alamkouh glacier in Iran was evaluated by means of several multi-temporal remote sensing images with a range of high to medium nominal scales from 1955 (aerial photos), 1997 (topographic map), 2002 (Terra-ASTER) and 2010 (LiDAR). The procedures of Digital Elevation Models (DEM) extraction from aerial photos and ASTER imagery were employed by using several Ground Control Points (GCPs) which were measured by Differential Global Positioning System (DGPS) from non-glaciated areas. For assessing and correcting these DEMs to quantify Alamkouh elevation changes, first a 3-D co-registration was applied to remove the systematic shifts from the four DEMs. After the 3-D co-registration, significant biases related to elevation were found in DEMs and the existing linear relationship between the elevation differences and elevation was used to adjust the DEMs. Finally, the morphometric changes were assessed for different dates by subtracting these adjusted DEMs. The present study came across some interesting findings, including the maximum thinning rate (about −4.5±0.32m/year) in high-elevated areas which fell down to about −0.5±0.06m/year toward the tongue of the glacier between 1955 and 2010. The total volume loss during this period (1955–2010) is about 0.29±0.03km3 which the highest retreat (equal to 42% of total volumetric change) occurred during 1997–2002. The estimation of cross-sectional elevation changes confirm that the maximum glacier surface lowering has taken place in the middle of the glacier, and this rate has decreased toward the sides due to the thicker debris covers and large colluvial debris sources along the steeper and more unstable valley rocks, which could retard the melting rate.