Recent changes of the ablation tongue and glacier foreland at the Lys Glacier (Italian Alps)

The Lys Glacier (Monte Rosa Group) is the most monitored glacier of the Italian Alps since 1940, with very frequent field measurements of terminus variations and the longest annual reporting of supraglacial debris presence. The recent changes of the ablation tongue and glacier forefield of the Lys Glacier have been evaluated through remote sensing investigations and field surveys. Terminus fluctuations, volume and debris-coverage variations, ablation rates and debris-surface temperatures have been analyzed starting for the last decades. The glacier terminus resulted to be generally retreating (cumulate retreat from 1975 to 2003 of -99 m, with an average of -3.4 m/year), with a unique period of advance occurred between 1976 and 1985. The volume decreased of 15.4 x 10-6 m3 in the considered time interval (1975-2003) and the supraglacial debris coverage resulted to be strongly increased due to several rock-fall events affecting the rock walls dominating the glacier tongue. The measured surface temperature correlates with debris thicknesses (r = 0.8). Supported by this agreement, a map representing the spatial distribution and thickness of debris cover was obtained from the ASTER-derived surface temperature data (TIR band) using the relationship between debris-surface temperature and thickness. Changes in the proglacial area have been analyzed through geomorphological investigations and dendrochronological dating. As regards the glacier forefield developed from the end of the Little Ice Age to the end of the 20th century, the correlation between dendrochronological and climatic and glaciological data (terminus variations) allowed to investigate the glacier response and ecesis time. The ongoing research on the most recent deglaciated forefield will contribute to a better understanding of tree colonization following the Lys Glacier ongoing retreat that will be compared with data already available for other alpine glaciers.