Alps; glacial erosion; cosmogenic nuclides; 10Be 14C 36Cl; Last Glacial Maximum; Lateglacial; Holocene;
Wirsig Christian, Zasadni Jerzy, Ivy‐Ochs Susan, Christl Marcus, Kober Florian, Schlüchter Christian (2016), A deglaciation model of the Oberhasli, Switzerland, in Journal of Quaternary Science
, 31(1), 46-59.
Wirsig Christian, Susan Ivy-Ochs, Akçar Naki, Lupker Maarten, Hippe Kristina, Wacker Lukas, Vockenhuber Christof, Schlüchter Christian (2016), Combined cosmogenic 10Be, in situ 14C and 36Cl concentrations constrain Holocene history and erosion depth of Grueben glacier (CH), in Swiss Journal of Geosciences
, 109(3), 379-388.
Wirsig Christian, Zasadni Jerzy, Christl Marcus, Akçar Naki, Ivy-Ochs Susan (2016), Dating the onset of LGM ice surface lowering in the High Alps, in Quaternary Science Reviews
, 143, 37-50.
Wirsig Christian, Susan Ivy‐Ochs Susan, Reitner Jürgen, Christl Marcus, Vockenhuber Christof, Bichler Mathias, Reindl Martin, Subglacial abrasion rates at Goldbergkees, Hohe Tauern, Austria, determined from cosmogenic 10Be and 36Cl concentrations, in Earth Surface Processes and Landforms
Glaciers have shaped the Alps. The landforms we see, such as U-shaped glacial troughs, trough shoulders and cirques, the marked relief, as well as the overall elevation of the Alps can all be attributed to the action of glaciers. Never-the-less, relatively little is known about the rates and patterns in space and time of how the process of subglacial erosion works. Quite fundamental questions such as: How long did it take for glaciers to carve the deep troughs and overdeepenings?, How did the trough shoulder itself form?, How do cirques evolve? remain unanswered. The goal of this proposal is to quantify the fundamental process of subglacial erosion. We propose to combine detailed understanding of the morphologic setting in the chosen study sites based on field mapping and DEM analyses with cosmogenic nuclide determinations and modeling. We specifically choose the unique combination of 10Be, 14C, and 36Cl in bedrock because of their different characteristics; markedly different half-lives (14C t½=5730 years, 36Cl t½=300,000 years, 10Be t½=1,390,000 years) and distinctly different production depth profiles. Production of 36Cl does not drop off as rapidly with depth in rock as does 10Be and 14C thus 36Cl can be used more effectively than the other two to quantify how much rock has been removed during glaciations. 14C decays much more rapidly than the other two nuclides, therefore it can be used to constrain how long a site has been covered by ice over the last 15-20 kyr. The inclusion of in-situ produced 14C in such studies is critical and very few research groups have this capability. For this investigation, we have chosen two study areas in the Alps, specifically Grimsel/Haslital region (Switzerland) and Zillertal (Austria) in which we will focus on the following basic questions in Alpine Quaternary geology and geomorphology:1) Was post-LGM (Last Glacial Maximum) ice surface lowering in the high Alps simultaneous with foreland deglaciation? We will exposure date truncated bedrock spurs and high-elevation erratics in Haslital and Zillertal with 10Be and 36Cl to address this question. 2) Was glacial erosion on the sides of the trough dominated by abrasion? The valley walls may have been formed during repeated pre-LGM glaciations and were only polished during the LGM. This will be tested by looking for inherited 36Cl and 10Be (nuclides acquired before the LGM) in the polished bedrock walls of Haslital and Zillertal. 3) What is the origin of the trough shoulder and the trough kante (edge of the trough)? Are they relict features? In that case 10Be and 36Cl concentrations in bedrock from the trough shoulder would contain inheritance. We plan to compare these landforms in the two study regions.4) Do cirques really evolve more through headwall retreat than from downwearing of the bed? If this is true bedrock on the outermost margin of a cirque may still contain nuclides, 10Be and especially 36Cl, acquired during the Lateglacial prior to Holocene readvances. Nuclide concentrations should decrease going in an up-glacier direction. In this regard 14C is crucial as it will show us the length of time that the cirque glacier was expanded (and the site was covered) during the Holocene. We have already chosen first sites, additional sites will be carefully evaluated based on field investigations and DEM analyses. A key component of the proposed study is the modelling of periods of exposure, coverage and depth of glacial erosion into the bedrock based on the obtained radionuclide data. The proposal investigators and collaborators have decades of experience in the interpretation of glacial landscapes in the Alps and application of cosmogenic nuclides in glacial geomorphological studies. The nuclide modeling will therefore be strictly constrained by plausible scenarios for periods of glacier expansion based on the known field record. We are uniquely positioned in the international community to use the three cosmogenic nuclides, 10Be, 14C and 36Cl, to study glacial erosion and the timing of glacial occupation.