Lateglacial Glaciers and Climate in the Silvretta Mountains, Western Austria
by
Andreas Hertl
Department of Geography, University of Innsbruck, Austria
Coauthors: Hanns Kerschner (Department of Geography, University of Innsbruck, Austria)

The Austrian Silvretta mountains are situated in the central Alps in western Austria along the border to Switzerland. High annual precipitation sums in the W and much less pre-cipitation in the E are due to their position at the western margin of the Central Alps close to the Rhine valley and Lake Constance. Present-day glacierization is still exten-sive in the higher parts and was more widespread during the "Little Ice Age" (LIA, 1850). Due to their position between the well-mapped areas in neighbouring Grisons (Switzerland) and the Northern Alps, they are of particular interest for studies of the lateglacial glacier and climate history.

Detailed mapping of the abundant lateglacial and early holocene moraines with classical methods shows that they can be correlated with the Clavadel (Oldest Dryas), Daun (Oldest Dryas)[1], Egesen (Younger Dryas)[2] and Kromer (earliest Preboreal ?) sta-dials of the Alpine Lateglacial Chronology. The type locality of the Kromer Stadial (Kromer valley)[3] is situated within the research area. Past glacier topographies are re-constructed with the help of the theoretical long profile of a glacier tongue [4]. They provide the basis for the calculation of steady-state equilibrium line altitudes (ELA) with an accumulation area ratio of 0.67 [3]. ELA depressions are calculated relative to the ELA of 1850, which is well documented in the research area.

The results show that the glacier extent during the Younger Dryas Egesen Stadial was much more extensive than previously assumed. The Egesen Stadial was clearly three-phased (E I - III). In the central part a dendritic glacier occupied most of the area dur-ing E I and E II, whereas local glaciers dominated during E III. During all substages the ELA showed an overall rise from W to E. The ELA depression increased from val-ues, which are typical for the central Alps, towards surprisingly large values in the W. The zone of the strongest gradient of the ELA and ELA depression was located in the central part of the research area during E I and shifted westwards during the later sub-stages (E II and E III). In contrast, during the Kromer Stadial, the ELA depression was spatially homogeneous.

From ELA-depressions, the palaeoprecipitation patterns can be calculated with a glacier-climate model [5] under the reasonable assumption of a spatially homogeneous summer temperature depression. For the Younger Dryas, a constant summer temperature depres-sion of -3.5 K is assumed, which is based on timberline depression [6]. As a result, an-nual precipitation sums seem to have been higher than today (+20 %) in the western part of the research area and less than today (-15%) in the eastern part during E I (early Younger Dryas). During later phases of the Egesen Stadial, precipitation sums generally decreased, but the spatial pattern remained roughly similar. The zone with the steepest precipitation gradient shifted northwestwards. This agrees well with the Early Younger Dryas precipitation pattern in the central Alps of Austria and Switzerland [7].

The overall precipitation pattern suggests that a more zonal atmospheric circulation pattern prevailed during the Younger Dryas, as it is predicted from numerical AGCM modelling and from terrestrial evidence from northwestern Europe [8, 9].

This study was funded by the European Commission (ENV4-CT98-5105 (DG12/ASAL) and the Austrian Science Foundation (P12600-GEO).

[1] Maisch, M. 1982: Geogr. Helv. 37(2), 93 - 104. [2] Ivy-Ochs, S. et al. 1996: Ecl. Geol. Helv. 89(3), 1049 - 1063. [3] Gross, G. et al. 1977: Z. Gletschkd. Glazgeol. 12(2), 223 - 251. [4] Nye, J.F. 1952: J. Glaciol. 2(12), 103 - 107. [5] Ohmura et al. 1992: J. Glaciol 38(130), 397-411. [6] Burga, C. & R. Perret. 1998: Vegetation und Klima der Schweiz. Thun: Ott. [7] Kerschner, H. et al. 2000: Ann. Glaciol. 31, 80 - 84. [8] Renssen, H. & R.F.B. Isarin. 1998: Clim. Dyn. 14, 33 - 44. [9] Isarin, R.F.B. et al. 1997: Palaeo3 134(1-4), 127 - 148.

Date received: March 28, 2001

Copyright © 2001 by the author(s). The author(s) of this work and the organizers of the conference have granted their consent to include this abstract in Topology Atlas. Document # cagc-44.