Alpine rock glacier activity over Holocene to modern timescales (western French Alps)
<p>Active rock glaciers are some of the most frequent cryospheric landforms in midlatitude high-elevation mountain ranges. Their activity strongly influences the hydrology and geomorphology of alpine environments over short (years to decades) and long (centuries to millennia) timescales. Being...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2022-06-01
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| Series: | Earth Surface Dynamics |
| Online Access: | https://esurf.copernicus.org/articles/10/605/2022/esurf-10-605-2022.pdf |
| _version_ | 1828325238406905856 |
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| author | B. Lehmann B. Lehmann R. S. Anderson X. Bodin D. Cusicanqui D. Cusicanqui P. G. Valla J. Carcaillet |
| author_facet | B. Lehmann B. Lehmann R. S. Anderson X. Bodin D. Cusicanqui D. Cusicanqui P. G. Valla J. Carcaillet |
| author_sort | B. Lehmann |
| collection | DOAJ |
| description | <p>Active rock glaciers are some of the most frequent cryospheric landforms in midlatitude high-elevation mountain ranges. Their activity strongly influences the hydrology and geomorphology of alpine environments over short (years to decades) and long (centuries to millennia) timescales. Being conspicuous expressions of mountain permafrost and important water
reserves in the form of ground ice, rock glaciers are seen as increasingly
important actors in the geomorphological and hydrological evolution of
mountain systems, especially in the context of current climate change. Over
geological timescales, rock glaciers both reflect paleoclimate conditions
and transport rock boulders produced by headwall erosion, and they therefore participate in shaping high mountain slopes. However, the dynamics of rock glaciers and their evolution over different timescales remain under-constrained.</p>
<p>In this study, we adopt a multi-method approach, including field
observations, remote sensing, and geochronology, to investigate the rock
glacier system of the Vallon de la Route (Combeynot Massif, western French Alps). Remotely sensed images and correlation techniques are used to document the displacement field of the rock glacier over timescales ranging from days to decades. Additionally, to estimate displacement over periods from centuries to millennia, we employ terrestrial cosmogenic nuclide (quartz <span class="inline-formula"><sup>10</sup>Be</span>) surface-exposure dating on rock boulder surfaces located along the central flow line of the rock glacier, targeting different longitudinal positions from the headwall to the rock glacier terminus.</p>
<p>The remote sensing analysis demonstrates that between 1960 and 2018 the two
lower units of the rock glacier were motionless, the transitional unit
presented an integrated surface velocity of <span class="inline-formula">0.03±0.02</span> m a<span class="inline-formula"><sup>−1</sup></span>, and the two upper active units above 2600 m a.s.l. showed a velocity between <span class="inline-formula">0.14±0.08</span> and <span class="inline-formula">0.15±0.05</span> m a<span class="inline-formula"><sup>−1</sup></span>. Our results show <span class="inline-formula"><sup>10</sup>Be</span> surface-exposure ages ranging from <span class="inline-formula">13.10±0.51</span> to <span class="inline-formula">1.88±0.14</span> ka. The spatial distribution of dated rock glacier boulders reveals a first-order inverse correlation between <span class="inline-formula"><sup>10</sup>Be</span> surface-exposure age and elevation and a positive correlation with horizontal distance to the headwall. These observations support the hypothesis of rock boulders falling from the headwall and remaining on the glacier surface as they are transported down valley, and they may therefore be used to estimate rock glacier surface velocity over geological timescales. Our results also suggest that the rock glacier is characterized by two major phases of activity. The first phase, starting around 12 ka, displays a <span class="inline-formula"><sup>10</sup>Be</span> age gradient with a rock glacier surface velocity of about 0.45 m a<span class="inline-formula"><sup>−1</sup></span>, following a quiescent period between ca. 6.2 and 3.4 ka before the emplacement of the present-day upper two active units. Climatic conditions have favored an integrated rock glacier motion of around 0.18 m a<span class="inline-formula"><sup>−1</sup></span> between 3.4 ka and present day. These results
allow us to quantify back-wearing rates of the headwall of between 1.0 and
2.5 mm a<span class="inline-formula"><sup>−1</sup></span>, higher than catchment-integrated denudation rates estimated over millennial timescales. This suggests that the rock glacier system promotes the maintenance of high rock wall erosion by acting as debris conveyor and allowing freshly exposed bedrock surfaces to be affected by erosion processes.</p> |
| first_indexed | 2024-04-13T19:18:25Z |
| format | Article |
| id | doaj.art-cc3653f3701944eeadfa61b449b89fee |
| institution | Directory Open Access Journal |
| issn | 2196-6311 2196-632X |
| language | English |
| last_indexed | 2024-04-13T19:18:25Z |
| publishDate | 2022-06-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Earth Surface Dynamics |
| spelling | doaj.art-cc3653f3701944eeadfa61b449b89fee2022-12-22T02:33:36ZengCopernicus PublicationsEarth Surface Dynamics2196-63112196-632X2022-06-011060563310.5194/esurf-10-605-2022Alpine rock glacier activity over Holocene to modern timescales (western French Alps)B. Lehmann0B. Lehmann1R. S. Anderson2X. Bodin3D. Cusicanqui4D. Cusicanqui5P. G. Valla6J. Carcaillet7CNRS, EDYTEM, Université Savoie Mont Blanc, 73000, Chambéry, FranceINSTAAR and Department of Geological Sciences, University of Colorado Boulder, Boulder, CO 80309, USAINSTAAR and Department of Geological Sciences, University of Colorado Boulder, Boulder, CO 80309, USACNRS, EDYTEM, Université Savoie Mont Blanc, 73000, Chambéry, FranceCNRS, EDYTEM, Université Savoie Mont Blanc, 73000, Chambéry, FranceCNRS, IRD, IGE, Université Grenoble Alpes, CS 40700 38 058 Grenoble CEDEX 9, FranceCNRS, IRD, IFSTTAR, ISTerre, Université Grenoble Alpes, Université Savoie Mont Blanc, 38000, Grenoble, FranceCNRS, IRD, IFSTTAR, ISTerre, Université Grenoble Alpes, Université Savoie Mont Blanc, 38000, Grenoble, France<p>Active rock glaciers are some of the most frequent cryospheric landforms in midlatitude high-elevation mountain ranges. Their activity strongly influences the hydrology and geomorphology of alpine environments over short (years to decades) and long (centuries to millennia) timescales. Being conspicuous expressions of mountain permafrost and important water reserves in the form of ground ice, rock glaciers are seen as increasingly important actors in the geomorphological and hydrological evolution of mountain systems, especially in the context of current climate change. Over geological timescales, rock glaciers both reflect paleoclimate conditions and transport rock boulders produced by headwall erosion, and they therefore participate in shaping high mountain slopes. However, the dynamics of rock glaciers and their evolution over different timescales remain under-constrained.</p> <p>In this study, we adopt a multi-method approach, including field observations, remote sensing, and geochronology, to investigate the rock glacier system of the Vallon de la Route (Combeynot Massif, western French Alps). Remotely sensed images and correlation techniques are used to document the displacement field of the rock glacier over timescales ranging from days to decades. Additionally, to estimate displacement over periods from centuries to millennia, we employ terrestrial cosmogenic nuclide (quartz <span class="inline-formula"><sup>10</sup>Be</span>) surface-exposure dating on rock boulder surfaces located along the central flow line of the rock glacier, targeting different longitudinal positions from the headwall to the rock glacier terminus.</p> <p>The remote sensing analysis demonstrates that between 1960 and 2018 the two lower units of the rock glacier were motionless, the transitional unit presented an integrated surface velocity of <span class="inline-formula">0.03±0.02</span> m a<span class="inline-formula"><sup>−1</sup></span>, and the two upper active units above 2600 m a.s.l. showed a velocity between <span class="inline-formula">0.14±0.08</span> and <span class="inline-formula">0.15±0.05</span> m a<span class="inline-formula"><sup>−1</sup></span>. Our results show <span class="inline-formula"><sup>10</sup>Be</span> surface-exposure ages ranging from <span class="inline-formula">13.10±0.51</span> to <span class="inline-formula">1.88±0.14</span> ka. The spatial distribution of dated rock glacier boulders reveals a first-order inverse correlation between <span class="inline-formula"><sup>10</sup>Be</span> surface-exposure age and elevation and a positive correlation with horizontal distance to the headwall. These observations support the hypothesis of rock boulders falling from the headwall and remaining on the glacier surface as they are transported down valley, and they may therefore be used to estimate rock glacier surface velocity over geological timescales. Our results also suggest that the rock glacier is characterized by two major phases of activity. The first phase, starting around 12 ka, displays a <span class="inline-formula"><sup>10</sup>Be</span> age gradient with a rock glacier surface velocity of about 0.45 m a<span class="inline-formula"><sup>−1</sup></span>, following a quiescent period between ca. 6.2 and 3.4 ka before the emplacement of the present-day upper two active units. Climatic conditions have favored an integrated rock glacier motion of around 0.18 m a<span class="inline-formula"><sup>−1</sup></span> between 3.4 ka and present day. These results allow us to quantify back-wearing rates of the headwall of between 1.0 and 2.5 mm a<span class="inline-formula"><sup>−1</sup></span>, higher than catchment-integrated denudation rates estimated over millennial timescales. This suggests that the rock glacier system promotes the maintenance of high rock wall erosion by acting as debris conveyor and allowing freshly exposed bedrock surfaces to be affected by erosion processes.</p>https://esurf.copernicus.org/articles/10/605/2022/esurf-10-605-2022.pdf |
| spellingShingle | B. Lehmann B. Lehmann R. S. Anderson X. Bodin D. Cusicanqui D. Cusicanqui P. G. Valla J. Carcaillet Alpine rock glacier activity over Holocene to modern timescales (western French Alps) Earth Surface Dynamics |
| title | Alpine rock glacier activity over Holocene to modern timescales (western French Alps) |
| title_full | Alpine rock glacier activity over Holocene to modern timescales (western French Alps) |
| title_fullStr | Alpine rock glacier activity over Holocene to modern timescales (western French Alps) |
| title_full_unstemmed | Alpine rock glacier activity over Holocene to modern timescales (western French Alps) |
| title_short | Alpine rock glacier activity over Holocene to modern timescales (western French Alps) |
| title_sort | alpine rock glacier activity over holocene to modern timescales western french alps |
| url | https://esurf.copernicus.org/articles/10/605/2022/esurf-10-605-2022.pdf |
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