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Geological Society of America Special Paper 415 2006 The timing of glacier advances in the northern European Alps based on surface exposure dating with cosmogenic 10Be, 26Al, 36Cl, and 21Ne Susan Ivy-Ochs† Insitut für Teilchenphysik, ETH-Hönggerberg CH-8093 Zurich, Switzerland, and Geographisches Institut, Universität Zurich-Irchel, CH-8057 Zurich, Switzerland Hanns Kerschner Institut für Geographie, Universität Innsbruck, A-6020 Innsbruck, Austria Anne Reuther Insitut für Physische Geographie, Universität Regensburg, D-93040 Regensburg, Germany Max Maisch Geographisches Institut, Universität Zurich-Irchel, CH-8057 Zurich, Switzerland Rudolf Sailer Institut für Naturgefahren und Waldgrenzregionen, Bundesforschungs- und Ausbildungszentrum für Wald, A-6020 Innsbruck, Austria Joerg Schaefer Lamont Doherty Earth Institute, Palisades, New York 10964, USA Peter W. Kubik Hans-Arno Synal Paul Scherrer Institut, c/o Institut für Teilchenphysik, ETH Hönggerberg, CH-8093 Zürich, Switzerland Christian Schlüchter Geologisches Institut, Universität Bern, CH-3012 Bern, Switzerland ABSTRACT Exposure dating of boulder and bedrock surfaces with 10Be, 21Ne, 26Al, and 36Cl allows us to constrain periods of glacier expansion in the European Alps. The age of 155 ka from a boulder of Alpine lithology located in the Jura Mountains (Switzer- land) provides a minimum age for pre-LGM (Last Glacial Maximum), more exten- sive Alpine glaciations. During the LGM, glaciers expanded onto the foreland after 30 ka. By 21.1 ± 0.9 ka deglaciation had begun, and the Rhône Glacier abandoned the †E-mail: [email protected]. Ivy-Ochs, S., Kerschner, H., Reuther, A., Maisch, M., Sailer, R., Schaefer, J., Kubik, P.W., Synal, H., and Schlüchter, C., 2006, The timing of glacier advances in the northern European Alps based on surface exposure dating with cosmogenic 10Be, 26Al, 36Cl, and 21Ne, in Siame, L.L., Bourlès, D.L., and Brown, E.T., eds., In Situ–Produced Cosmogenic Nuclides and Quantifi cation of Geological Processes: Geological Society of America Special Paper 415, p. 43–60, doi: 10.1130/2006.2415(04). For permission to copy, contact [email protected]. © 2006 Geological Society of America. All rights reserved. 43 44 Ivy-Ochs et al. outer moraines. The age of 15.4 ± 1.4 ka provides a minimum age for formation of Gschnitz stadial moraines (Austria). They mark the fi rst clear post-LGM readvance of mountain glaciers, when glacier termini were already situated well inside the moun- tains. Glacier advance at the onset of the Younger Dryas led to formation of Egesen I moraines, dated to 12.2 ± 1.0 ka at the Schönferwall site (Austria) and to 12.3 ± 1.5 ka at the outer moraine at Julier Pass (Switzerland). The age of 11.3 ± 0.9 ka for the inner moraine / rock glacier complex at Julier Pass corroborates the fi eld evidence, which points to a marked increase in rock glacier activity and delayed moraine stabilization during the late Younger Dryas. An early Preboreal glacier advance, larger than the Little Ice Age advance(s) at 10.8 ± 1.0 ka, was recorded at Kartell cirque (Austria). A moraine doublet located a few hundred meters outside the A.D. 1850 moraines in Kromer Valley (Austria) was dated at 8.4 ± 0.7 ka. At least during termination 1, gla- cier volumes in the Alps varied in tune with climate oscillations, Heinrich event 1, the Younger Dryas cold phase, the Preboreal oscillation, and the 8.2 ka event. Keywords: cosmogenic nuclides, LGM, Alpine Lateglacial, Holocene, glacier varia- tions, moraine. INTRODUCTION directly (Gosse and Phillips, 2001), making surface exposure dat- ing invaluable in formerly glaciated areas (Gosse, 2005; Reuther At the beginning of the twentieth century, the classical et al., 2006). fourfold system for the glaciations of the Alps was presented by In this paper, we summarize the present state of knowledge Penck and Brückner (1901/1909). Distinct morphostratigraphic on periods of glacier expansion in the Alps that have been tempo- elements (for the most part terraces and moraines) located on rally constrained using the cosmogenic nuclides 10Be, 21Ne, 26Al, the northern forelands of the Alps were the basis for setting up and 36Cl. Refl ecting the locations of the sites, the focus here is the following system: (1) Günz, as defi ned by older (or higher) on the northern regions of the Alps. We discuss in detail eight “Deckenschotter” (cover gravel) deposits, (2) Mindel, as defi ned sites: Montoz pre-LGM (Last Glacial maximum) boulders (Jura by younger (or lower) Deckenschotter deposits, (3) Riss, defi ned Mountains, Switzerland), the Wangen an der Aare LGM moraine by moraine remnants and outwash related to the high terraces (Solothurn, Switzerland), Grimsel Pass (Bern/Wallis, Switzer- (Hochterrasse), and (4) Würm, delineated by moraines and out- land), the Trins Gschnitz moraine (Tyrol, Austria), Daun and wash of the low terraces (Niederterrasse). Egesen moraines at Julier Pass (Graubünden, Switzerland), the The Riss and Würm glacial periods were separated by the Egesen I Schönferwall moraine (Tyrol, Austria), and the Kartell last interglacial. The system was subsequently expanded and (Tyrol, Austria) and Kromer (Vorarlberg, Austria) moraines. We repeatedly revised. Buoncristiani and Campy (2004), Fiebig et discuss the exposure dating results in the context of the chron- al. (2004), Schlüchter (2004), and van Husen (2004) summarize ological framework of climate variations in the Alps and their the present state of knowledge. Terminal moraines and associated vicinity. Specifi c site locations for the related radiocarbon, lumi- deposits formed during the Last Glacial Maximum (late Würm) nescence, and U/Th dates are found in the references given. provide the most important morphological reference point in the forelands of the Alps (Fig. 1). The fi nal disintegration of the fore- METHODS land piedmont glaciers marks the start of the “Alpine Lategla- cial” as defi ned by Penck and Brückner (1901/1909). During the Rock surfaces were sampled for exposure dating with ham- Alpine Lateglacial, glaciers readvanced several times to succes- mer and chisel. Except where indicated, the fl at tops of the larg- sively smaller extents (“stadials”), building prominent moraine est boulders were sampled. Details on sample preparation can systems in the valleys and cirques (Table 1). be found in Ivy-Ochs (1996) and Ochs and Ivy-Ochs (1997). Temporal constraints for deciphering the timing of glacier Ratios of the radionuclide to stable nuclide were measured variations have been provided by luminescence methods, radio- using accelerator mass spectrometry (AMS) at the PSI/ETH carbon, U/Th, and surface exposure dating with in situ–produced Zurich tandem accelerator facility (Synal et al., 1997). Neon cosmogenic nuclides (cf. Preusser, 2004). Each dating method isotopes were analyzed at the Institute of Isotope Geology and has its own niche and optimum age range, which is determined Mineral Resources of the ETH Zurich following the protocol by both geological circumstances (such as the material that can be given by Bruno et al. (1997). dated and its geological setting) and methodological constraints The exposure ages presented here are based on half-lives of (e.g., the half-life of the nuclides). With surface exposure dating, 1510 k.y. (10Be), 716 k.y. (26Al), and 301 k.y. (36Cl). The produc- the rock surfaces created during glacier variations can be dated tion rates used for the age calculations are listed in Table 2. Major Alpine glaciationsbasedoncosmogenicnuclides of Timing 45 06°09’ 09°32’ 13°02’ 15°26’ Stuttgart Linz 48°18’ Munich 48°18’ Isar- Inn Salzach Rhine Loisach Traun Basel Iller- Zurich Lech Lake Constance M Rh-Linth Innsbruck S Reuss Gz K Graz Bern 46°51’ Rhone(N) Chur 46°51’ Gr A J Geneva Lake Geneve Ljubiljana Rhone(S) Garda Milano Lake 45°04’ 45°04’ Monaco 0100km50 N Source: SRTM Data 06°09’ 09°32’ 13°02’ 15°26’ Figure 1. View of the Alps from Shuttle Radar Topographic Mission data. LGM ice extent based on Ehlers and Gibbard (2004). The main piedmont lobes of the northern forelands are la- beled. Location of sites investigated with cosmogenic nuclides are indicated by the circles. The yellow circles stand for data discussed in detail in this paper. The white circles represent data from other studies. M—Montoz (this paper); S—Solothurn (Ivy-Ochs et al., 2004); Gr—Grimsel Pass (Ivy-Ochs, 1996; Kelly et al., 2006); A—Grosser Aletsch Glacier (Kelly et al., 2004b); J—Julier Pass (Ivy-Ochs et al., 1996, 1999); K—Kromer (Kerschner et al., 2006), Kartell and Schönferwall (this paper); Gz—Trins Gschnitz moraine (Ivy-Ochs et al., 2006). 46 Ivy-Ochs etal. TABLE 1. SUMMARY OF THE LATEGLACIAL STADIALS, EUROPEAN ALPS Stadial Moraine and glacier characteristics Regional situation ELA depression Time-stratigraphic position Kromer Well-defi ned, blocky, multi-walled moraines, small rock glaciers.