Reconstruction of the dynamics and origin of rock glaciers in an Alpine environment
Authors: Lehmann Benjamin , Anderson Robert S. , Bodin Xavier , Valla Pierre G. , Carcaillet Julien 
Published: March 2021

&lt;p&gt;Rock glaciers are one of the most frequent cryospheric landform in mid-latitude mountain ranges. They influence the evolution of alpine environments on short (years to decades) and long (centuries to millennia) time scales. As a visible expression of mountain permafrost [1] as well as an important water reserve in the form of ground ice [2], rock glaciers are seen as increasingly important in the evolution of geomorphology and hydrology of mountain systems in the context of climate change and deglaciation [3, 4]. On longer time scales, rock glaciers transport boulders produced by the erosion of the headwall upstream and downstream and therefore participate in shaping mountain slopes [5]. Despite their importance, the dynamics and origin of rock glaciers are poorly understood.&lt;/p&gt;&lt;p&gt;In this study, we propose to address two questions:&lt;/p&gt;&lt;p&gt;1) How does the dynamics of rock glaciers change over time?&lt;/p&gt;&lt;p&gt;2) What is the origin of rock glaciers and what is their influence on the evolution of alpine environments?&lt;/p&gt;&lt;p&gt;These two questions require an evaluation of the surface velocity field of rock glaciers by relating short and long time scales. To solve this problem, we combine complementary methods including remote sensing, geochronology with a mechanical model of rock glacier dynamics. We apply this approach to the rock glacier complex of the Vallon de la Route in the Massif du Combeynot (French alps).&lt;/p&gt;&lt;p&gt;In order to reconstruct the displacement field of the rock glacier on modern time scales, we used remote sensing methods (i.e., image correlation and InSAR). Over longer periods (10&lt;sup&gt;3&lt;/sup&gt; to 10&lt;sup&gt;4&lt;/sup&gt; years), we used cosmogenic terrestrial nuclides (TCN) dating. By applying this methodology to boulder surfaces at different positions along the central flow line of the rock glacier, from the headwall to its terminus, we will be able to convert the exposure ages into surface displacement. The use of dynamic modelling of rock glaciers [6] will allow us to relate the surface kinematics to short to long time scales. It will then be possible to discuss the age, origin of rock glaciers and how topo-climatic and geomorphological processes control their evolution in Alpine environment.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;[1] Barsch, D.: Rockglaciers. Indicators for the Present and Former Geoecology in High Mountain Environments, Springer series in physical environment vol. 16, Springer, Berlin, Heidelberg, 1996.&lt;/p&gt;&lt;p&gt;[2] Jones, D. B., Harrison, S., Anderson, K., and Whalley, W. B.: Rock glaciers and mountain hydrology: A review, Earth-Sci Rev, 193, 66&amp;#8211;90, 2019.&lt;/p&gt;&lt;p&gt;[3] Haeberli, W., Schaub, Y., and Huggel, C.: Increasing risks related to landslides from degrading permafrost into new lakes in deglaciating mountain ranges, Geomorphology, 293, 405&amp;#8211;417, 2017.&lt;/p&gt;&lt;p&gt;[4] Knight, J., Harrison, S., and Jones, D. B.: Rock glaciers and the geomorphological evolution of deglacierizing mountains, Geomorphology, 324, 14&amp;#8211;24, 2019.&lt;/p&gt;&lt;p&gt;[5] MacGregor, K.R., Anderson, R.S., Waddington, E.D.: Numerical modeling of glacial erosion and headwall processes in alpine valleys. Geomorphology 103 (2):189&amp;#8211;204, 2009.&lt;/p&gt;&lt;p&gt;[6] Anderson, R. S., Anderson, L. S., Armstrong, W. H., Rossi, M. W., &amp; Crump, S. E.: Glaciation of alpine valleys: The glacier&amp;#8211;debris-covered glacier&amp;#8211;rock glacier continuum. Geomorphology, 311, 127-142, 2018.&lt;/p&gt;