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International audience; To calibrate the in situ 10Be production rate, we collected surface samples from nine large granitic boulders within the deposits of a rock avalanche that occurred in AD 1717 in the upper Ferret Valley, Mont Blanc Massif, Italy. The 10Be concentrations were extremely low and successfully measured within 10% analytical uncertainty or less. The concentrations vary from 4829 ± 448 to 5917 ± 476 at g−1. Using the historical age exposure time, we calculated the local and sea level‐high latitude (i.e. ≥60°) cosmogenic 10Be spallogenic production rates. Depending on the scaling schemes, these vary between 4.60 ± 0.38 and 5.26 ± 0.43 at g−1 a−1. Although they correlate well with global values, our production rates are clearly higher than those from more recent calibration sites. We conclude that our 10Be production rate is a mean and an upper bound for production rates in the Massif region over the past 300 years. This rate is probably influenced by inheritance and will yield inaccurate (e.g. too young) exposure ages when applied to surface‐exposure studies in the area. Other independently dated rock‐avalanche deposits in the region that are approximately 103 years old could be considered as possible calibration sites.

Poster

International audience; On 12 September AD 1717, a rock volume larger than 10 million m3 collapsed onto the Triolet Glacier, mobilized a mass composed of ice and sediment and travelled more than 7 km downvalley in the upper Ferret Valley, Mont Blanc Massif (Italy). This rock avalanche destroyed two small settlements, causing seven casualties and loss of livestock. No detailed maps were made at the time. Later investigators attributed accumulations of granitic boulders and irregular ridges on the upper valley floor to either glacial deposition, or the AD 1717 rock avalanche, or a complex mixture of glacial deposition, earlier rock avalanche and AD 1717 rock avalanche origin. In this study, we present cosmogenic 10Be exposure ages from nine boulders in the extensive chaotic boulder deposit with irregular ridges, two from Holocene glacier-free areas, and one from a Little Ice Age moraine. Exposure ages between 330 ± 23 and 483 ± 123 a from eight of nine boulders from the chaotic deposit indicate that at least seven were deposited by the AD 1717 rock avalanche. The other three boulders yielded 10Be exposure ages of 10 900 ± 400, 9700 ± 400 and 244 ± 97 a, respectively. Our results are in good agreement with the existing chronology from dendrochronology and lichenometry, and radiocarbon analysis of wood samples, but not with older 14C ages from a peat bog in the upper part of the valley. Based on the new age control, the rock avalanche deposits cover the whole bottom of the upper Ferret valley. Copyright © 2012 John Wiley & Sons, Ltd.

International audience; The granitic deposit of the upper Val Ferret was shown in 1980 to result from a large September 1717 rock avalanche. A huge volume of rock and ice travelled onto the Triolet Glacier>7 km downvalley. Boulder accumulations and irregular ridges spread out over a distance of 2 km on the valley floor terminate with an arcuate front. A 2009 reconstruction with radiocarbon dating proposed a smaller lateral extension of the landslide on the valley floor preserving Lateglacial moraines, but cosmogenic exposure dating questions it. Consistency of 10Be dates suggests that the deposit results from the 1717 rock avalanche, with a rock volume>10×106 m3, and a likely similar ice volume. The importance of rock avalanches has to be emphasised to help to prevent risk in inhabitated valleys. Even for the recent period, the contribution of cosmogenic exposure dating to geomorphological analysis of complex landform assemblages is valuable.

Anatolia is situated in the Eastern Mediterranean region between 36 – 42N and 26 – 45E. The geological records of paleoglaciations in the high terrains of Anatolia are key archives to quantify paleoclimate change in the Eastern Mediterranean area. The climate of the Eastern Mediterranean region is influenced by three main atmospheric systems: the main middle to high latitude westerlies, the mid-latitude subtropical high-pressure systems, and the monsoon climate. Glacial geological studies in Turkey have started in the late 19th century. Glacial deposits are found mainly in the eastern, northeastern and southern part of the Anatolian Peninsula. Anatolia is the fundamental element to understand the interactions between paleoenvironment, climatic variations, and development of the human societies. As the Taurus and Black Sea Mountains are sensitively situated for the paleoclimatic reconstructions, a chronostratigraphic framework on the paleoglaciation should be elaborated. The timing of the Last Glacial Maximum (LGM) in Anatolia is still unknown. Our first results from Kavron Valley (Kaçkar Mountains, NE Turkey) are encouraging for the reconstruction of paleoglaciations in Turkey and related paleoclimatological interpretations although it is presently difficult to pinpoint the classical Last Glacial Maximum – Younger Dryas – Little Ice Age moraine sequences in the field., Die spezielle geographische Lage der Türkei nordöstlich vom Mittelmeer zwischen 36 und 42 N, bzw. zwischen 26 und 45 E macht sie für Klima- und Paläoklimastudien zu einem besonders zentralen und sensiblen Gebiet. Der Vergletscherungsgeschichte von Anatolien kommt demzufolge eine Schlüsselrolle bei der Bewertung von Klimaveränderungen im östlichen Mittelmeerraum zu. Bereits aus dem späten 19. Jahrhundert sind glazialgeologischse Studien aus der Türkei bekannt. Vergletscherungsspuren sind vorwiegend in den östlichen, nordöstlichen und südlichen Gebirgszügen von Kleinasien vorhanden: in den Gebirgen am Schwarzen Meer, im Taurus, in den ostanatolischen Bergen, dem Uludağ und auf isolierten Vulkanen wie Erciyes, Süphan und Ararat. Das Klima im östlichen Mittelmeerraum ist hauptsächlich durch drei atmosphärische Strömungen geprägt: westliche Höhenströmungen der mittleren und höheren Breiten, subtropische Hochdruckgebiete der mittleren Breiten und der Monsun. Der Transport von Feuchtigkeit ist die zentrale Bestimmungsgröße für die Niederschlagsverteilung in diesem Gebiet. Für die Feuchtigkeitszufuhr in die Gebirge Kleinasiens während der pleistozänen Kaltzeiten sind Lage und Maxima der Jetstreams wichtig. Gletscher und ihre Ablagerungen sind in diesem Zusammenhang zentrale Archive für Klimarekonstruktionen Amplitude und Frequenz von eiszeitlichen Gletscherschwankungen müssen möglichst präzise erfasst werden, um Aussagen über die eiszeitliche atmosphärischen Zirkulationen – wie in den Alpen – machen zu können. Dies ist für Kleinasien auch zudem wichtig und interessant, weil diese Gegend seit Jahrtausenden intensive besiedelt ist. Das Alter der letzten maximalen Vereisung in Anatolien ist bisher unbekannt. Unsere ersten Ergebnisse aus dem Kavrontal (Kaçkar Gebirge, NE Türkei) sind vielversprechend in bezug auf die Rekonstruktion früherer Vergletscherungen in der Türkei und daraus folgenden Interpretationen über die paläoklimatologischen Verhältnisse. Es ist im Augenblick jedoch schwierig die im Gelände unterscheidbaren Moränensequenzen mit den klassischen Vereisungsstadien (Letztes Glaziales Maximum, Jüngere Dryaszeit, Kleine Eiszeit) zu verknüpfen.