Rock glacier permafrost in the Central Andes of Argentina (PermArg): regional distribution - ice content - hydrological significance
Final Report Abstract
In the central arid to semi-arid Andes (30–33°S), where human livelihoods critically depend on meltwaters from snow and ice quantitative data on potential water resources are a prerequisite for the development of a suitable adaptation strategy. Apart from glaciers, there is growing evidence that the assemblage of periglacial landforms with its invisible underground ice resources also plays an important role in mountain hydrology. Rock glaciers predominate in the landscape and often outnumber glaciers in the Central Andes. We investigated 295 rock glaciers and ice-debris complexes with feature tracking in optical satellite imagery and a random forest classification approach. Mean surface velocities of rock glaciers vary between 0.37 and 2.61 m yr^-1 showing significantly higher average speeds compared to the European Alps, Tien Shan or the Sierra Nevada. Based on our further research questions we estimated volumetric ice and water content in selected active rock glaciers in both study sites, Morenas Coloradas (Mendoza) and Agua Negra (San Juan), respectively. For the first time in the central Andes of Argentina we obtained quantitative data on the ice content of rock glaciers showing that these landforms have not only large water storage capacities but show also significant interannual changes. We used complementary data from our extensive geophysical surveys (electrical resistivity tomography and seismic refraction tomography) to apply a petrophysical four-phase model (4PM). Our results show generally very heterogeneous ice and water contents with partly very ice-rich permafrost and supra-, intra- and subpermafrost water pathways at the end of the thaw period in late summer. Both, active layer and ice-rich permafrost within the rock glacier control traps and pathways of shallow groundwater and thus regulates interannual storage changes and water releases. The combined use of surface (e.g. structure from motion analysis) and subsurface methods (geophysical methods and 4PM modeling) is highly recommended to identify spatial surface patterns and changes and potential relationships to internal ice/hydrological structures. Horizontal surface deformations of up to 2 m yr^-1 prove the active status, whereas our 4PM allow calculating volumetric fractions of ice, water, air, and rock. Crucial for the successful application of the 4PM are the predefined porosities of the material and the good resolution of the obtained geophysical data. Thermokarst features with ponds on the surface are well displayed in the 4PM with high water contents in the near subsurface. Modelled ice-rich permafrost (> 40 %) bodies interchange with permafrost conditions of lower volumetric ice content and completely ice free sections. Thus, ice saturation varies spatially from 30 to 90 %. High water saturation (>25 %) was interpreted as seasonal groundwater within unfrozen areas. Increased water content could also be related local permafrost degradation. Negative and positive vertical surface changes show a heterogeneous spatial pattern of ice gains and losses within the period of observation (2016-2017 and 2017-2018). The interannual water storage changes of -36 mm yr^-1 in 2016-2017 and 28 mm yr^-1 in 2017-2018 correspond to only 2-4 % of the entire water content of the rock glacier at the end of the thaw period, but displays a significant amount compared to the mean annual precipitation (40-140 mm). This study demonstrates quantitatively the crucial role of rock glaciers in buffering, storing, and regulating seasonal groundwater flow and recharge. These landforms constitute a long-term ice storage, where currently only 2.8 % of the surface area remains covered by perennial firn and ice. Given the widespread distribution and much slower response of active rock glaciers to the observed and predicted temperature increase in the dry Andes compared to down-wasting glaciers, our results suggest that long-term water storages and seasonal buffers in ice-rich permafrost and the active layer, respectively, will become more important for Andean watersheds in the future.
Publications
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(2016): Internal structure of Morenas Coloradas rock glacier, Vallecitos, Central Andes of Argentia (33°S). 10th International Workshop of Young Geomorphologists. Werbellinsel, Germany
Halla, C., Blöthe, J.H. & Schrott, L.
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(2016): Rock glacier permafrost in the semi-arid Andes of Argentina. 11th International Conference on Permafrost. Potsdam, Germany
Halla, C., Blöthe, J.H., Schrott, L. & Trombotto, D.
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(2017): Surface Morphology, Internal Structure and Water Storage Capacities of Rock Glaciers in the Dry Central Andes of Argentina (30- 33°S). 4th Central European Geomorphology Conference. Bayreuth, Germany
Halla, C., Blöthe, J.H., Hauck, C., Trombotto, D. & Schrott, L.
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(2018): Assessing rock glacier horizontal movement in the Cordón del Plata range, Central Andes of Argentina: Proceedings of the 5th European Conference on Permafrost. Chamonix, Mont-Blanc, p. 384-385
Blöthe, J.H., Halla, C., Schwalbe, E., Trombotto, D., & Schrott, L.
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(2018): Permafrost in Argentiniens Anden - eine bedeutende hydrologische Ressource. Geographische Rundschau, 70, 36-40
Halla, C., Blöthe, J.H., Trombotto, D. & Schrott, L.
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(2018): Potential water storage of rock glacier permafrost derived from geophysical modeling (Central Andes of Argentina). EGU General Assembly 2018. Vienna, Austria
Halla, C., Blöthe, J.H., Hauck, C., Trombotto, D. & Schrott, L.
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(2018): Volumetric ice content in active rock glaciers derived from geophysical modeling (Central Andes of Argentina). 5th European Conference on Permafrost. Chamonix, Mont-Blanc, p. 886-887
Halla, C., Blöthe, J.H., Tapía-Baldis, C., Hauck, C. & Schrott, L.
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(2019): Regional analysis of ice-debris landform kinematics in the central Andes of Argentina. EGU General Assembly 2019. Vienna, Austria
Blöthe, J.H., Schwalbe, E., Halla, C., Bottegal, E., Trombotto, D. & Schrott, L.
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(2021): Ice content and interannual water storage changes of an active rock glacier in the dry Andes of Argentina. The Cryosphere, 15, 1187-1213
Halla, C., Blöthe, J.H., Tapia Baldis, C., Trombotto, D., Hilbich, C., Hauck, C., & Schrott, L.
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(2021): Surface velocity fields of active rock glaciers and ice-debris complexes in the Central Andes of Argentina. Earth Surface Processes and Landforms, 46(2), 504-522
Blöthe, J.H., Halla, C., Schwalbe, E., Bottegal, E., Trombotto Liaudat, D., & Schrott, L.
