"Whereas glacier advance is known during the ""Little Ice Age"" (1600-1850), their retreat in the 150 years that followed is no longer in doubt (example: surface of Gébroulaz in 1965: 420 ha and in 2009: 330 ha). Recent monitoring has given surprising results. The upper part of the glacier (above 3,100 m in altitude) has thickened by 20 metres! Explanation: the glacier passes through a rocky narrowing which compresses it laterally and causes it to swell artificially."