TIMING AND STRUCTURE OF THE LATE GLACIAL GSCHNITZ AND EGESEN GLACIER ADVANCES IN THE EUROPEAN ALPS

Starting around 19 ka, the LGM (Last Glacial Maximum) system of ice domes, ice streams and piedmont glaciers in the European Alps collapsed to a dendritic glacier system, then finally to valley glaciers. The sequence of late glacial glacier readvances; Bühl, Steinach, Gschnitz, Clavadel/Senders, Daun, Egesen, and Kromer/Kartell; was largely set-up more than 100 years ago. Late glacial moraines lie less than 20 km downvalley from the LIA (Little Ice Age) moraines and about 100 km upvalley from the LGM terminal positions.

The Gschnitz stadial is characterized by an ELA (equilibrium line altitude) drop of 650-700 m with respect to the reference LIA ELA. At Trins, the Gschnitz type locality in the eastern Alps, the moraine contains a large volume of sediment and has simple well-defined lateral moraines. The glacier did advance over largely ice-free terrain and maintained its position at Trins for up to several hundred years. 10Be surface exposure dates put the glacier advance at 15-16 ka; right around the time of Heinrich event 1. A weak second peak in the age distribution implies instability of the boulders well into the Younger Dryas.

Egesen stadial moraines demarcate glacier terminal positions 450 to 180 m below the LIA positions based on ELA, but this is strongly dependent on location in the Alps. Egesen moraine complexes are made up of several sharp-crested, bouldery ridges, that are infrequently cross-cutting. 10Be exposure ages from several sites indicate moraine stabilization around 11-12 ka, i.e. during the Younger Dryas. Timing of the Kromer/Kartell stadial, sometimes placed as the final phase of the Egesen, remains enigmatic. In the Ferwall group of the Eastern Alps, Kartell moraines, characterized by an ELA drop of 120 m, lie about 1 km downvalley from the LIA moraines and 1 km upvalley from the youngest local Egesen moraines. 10Be exposure ages around 10 ka, point to affinity with the Preboreal oscillation. In contrast, 10Be exposure ages for boulders atop the moraine at the type locality in the Kromer valley (ELA change -60 m) indicate the moraine formed during glacier advance 2 thousand years later.