Paper No. 139-1
Presentation Time: 9:00 AM
STRUCTURE AND TIMING OF EGESEN STADIAL GLACIER ADVANCES IN THE EUROPEAN ALPS
The time between the breakdown of the Last Glacial Maximum Alpine foreland piedmont lobes and the beginning of the Holocene comprises the ‘Alpine Lateglacial’. Glaciers re-advanced several times during this period with the final advance, the Egesen stadial, having deposited the most marked moraines. Moraines attributed to the Egesen stadial are found in valleys all across the Alps. Classification as an Egesen stadial moraine is based on location in valley morphostratigraphic sequence, equilibrium line altitude depression (ca. 250-400 m) with respect to the Little Ice Age equilibrium line altitude, and morphology of the moraines (Kerschner et al. 2000 and references therein). Egesen moraines are generally the first clear moraine set encountered down valley (up to a few tens of km) of the late Holocene/Little Ice Age moraines. The moraines are distinctive in that there are two, at some locations three, sets of nested moraines, with sharp-crested and blocky character. An origin in glacier advance in response to Younger Dryas cooling was long suspected. Dating attempts based on pollen and radiocarbon dating on bog sediments in the former tongue area, for example at Maloja Pass, gave first confirmation. Clear verification that the Egesen stadial moraines formed during the Younger Dryas came with the first cosmogenic nuclide surface exposure dating in the Alps at Julier Pass (Ivy-Ochs et al. 1996). Since then Egesen moraines have been exposure dated at sites ranging from the Maritime Alps (Federici et al. 2008) to the Eastern Alps of Austria (Ivy-Ochs et al. 2006). Never-the-less, the use of different 10Be production rates in the various publications may lead to confusion and mask true age relationships between the sites. Recent results from numerous Northern Hemisphere sites point overwhelmingly to a 10Be production rate of 4.0 10Be atoms per gram quartz per year (Heyman et al. 2014). Recalculation of 10Be exposure dates of Egesen sites in the Alps produced over the last 20 years with this production rate allows more insightful comparison of glacier response during the Younger Dryas in the Alps.