Il ghiacciaio del Ruitor (Valle d'Aosta) nella piccola Età Glaciale

The Ruitor glacier (Aosta Valley) during the Little Ice Age

Abstract

The maximum extent reached by the Ruitor glacier during the Little Ice Age (LIA) was reconstructed on the basis of a geomorphologic survey of marginal moraines, drift limits and erosional trimlines. At the LIA maximum the glacier was 27% larger than now (1991) and its terminus was at an altitude 370 m lower than the present. LIA melt-water streams and marginal lakes were identified. In particular the ice dammed Ruitor lake is well documented by shorelines, a delta moraine and by melt-water channels. Jökulhlaup coarse sediments have been observed just out of the max LIA moraines, possibly deposited by the last outburst (1751) from the ice dammed lake. On the base of historical documents the max LIA advance occurred between 1751 and 1864, possibly in phase with the 1820 advance shown by other Aosta valley glaciers, as previously suggested by Sacco. Pre-LIA Holocene moraines were also observed and preliminarily dated. The surface extent variations of the Ruitor glacier during the Holocene are bracketed between the maximum LIA and the minimum pre-Neoglacial, inferred from stratigraphic evidence. The Equilibrium Line Altitude variation was of about 150 m, a value in agreement with what observed in other Italian glaciers with a prevailing northern aspect.