Reconstructing recent environmental changes from proglacial lake sediments in the Western Alps (Lake Blanc Huez, 2543 m a.s.l., Grandes Rousses Massif, France) Emmanuel Chapron a, ⁎ , Xavier Faïn b , Olivier Magand b , Laurent Charlet c , Maxime Debret b , Marie Antoinette Mélières b a Geological Institute ETH, Universitätstrasse 16, CHN E23, CH-8092 Zürich, Switzerland b Laboratoire de Glaciologie et Géophysique de l’Environnement, UMR 5183, Domaine Universitaire, BP 96, F-38402 Saint Martin d’Hères, France c Laboratoire de Géophysique Interne et Tectonophysique, UMR 5559 CNRS, Observatory for Earth and Planetary Sciences (OSUG), Joseph Fourier University, BP 53, F-38041 Saint Martin d’Hères, France Received 11 October 2006; received in revised form 19 April 2007; accepted 28 May 2007 Abstract The evolution of high-altitude glaciers and human activities in the Grandes Rousses massif is documented by high-resolution seismic reflection profiling and multiproxy analysis of short sediment cores in proglacial Lake Blanc Huez. These lacustrine data are compared with historical chronicles, geomorphological features and glaciological studies in this region of the western Alps and they allow the documentation of recent environmental changes. The specific geometry of high-amplitude reflections in the uppermost seismic unit, the lithology of short cores and the available limnological data in the lake suggest that clastic particles eroded by the glaciers and transported in suspension by glacial melt waters in early summer essentially develop homopycnal flood events in the lake. A conceptual model linking fluctuations of glacier equilibrium line altitudes in the catchment area with sedimentary facies retrieved in the lake basin is proposed. This approach allows reconstructing continuous glacier fluctuations since AD1820–1850 and suggests several phases of glacier fluctuations during the Little Ice Age (LIA). These reconstructions are based on changes in lacustrine sediment laminations, density, magnetic susceptibility, reflectance spectra, organic matter and Arsenic content. The age-depth model of short sediment cores is provided by 210 Pb, 137 Cs and 241 Am radionuclide dating. This chronology is further supported by identifying in lacustrine sediments the impact of (i) the nearby M 5.3 Corrençon earthquake in AD 1962, (ii) the development of the ski resort at high-altitude close to the lake and (iii) the last advance of glaciers during the LIA in AD1820–1850 and the following phase of glacier retreat observed in the alpine region at the end of the LIA in AD 1880. Frequent sandy layers enriched in organic matter and associated with fluctuations in the Arsenic concentrations may result from hydraulic remobilisation of Middle Age mine tailings at the lake shore by snow melt or heavy rain fall events during the LIA. © 2007 Elsevier B.V. All rights reserved. Keywords: French Alps; Proglacial lakes; Little Ice Age; Seismic stratigraphy; Glacier fluctuations; High-altitude mining activities 1. Introduction The interaction of climate and human impact on Holocene environmental changes in the Alpine region and on clastic sediment delivery to lake basins is frequently Palaeogeography, Palaeoclimatology, Palaeoecology 252 (2007) 586 – 600 www.elsevier.com/locate/palaeo ⁎ Corresponding author. Tel.: +41 44 632 68 49; fax: +41 44 632 10 75. E-mail address: emmanuel.chapron@erdw.ethz.ch (E. Chapron). 0031-0182/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2007.05.015