Landslides as geological hotspots of CO<sub>2</sub> emission: clues from the instrumented Séchilienne landslide, western European Alps
<p>This study makes use of a highly instrumented active landslide observatory (9 years of data) in the French Alps, the Séchilienne slope. Here, we use a combination of major element chemistry and isotopes ratios (<span class="inline-formula"><sup>87</sup></span&...
Main Authors: | , , , , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2021-06-01
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Series: | Earth Surface Dynamics |
Online Access: | https://esurf.copernicus.org/articles/9/487/2021/esurf-9-487-2021.pdf |
Summary: | <p>This study makes use of a highly instrumented active
landslide observatory (9 years of data) in the French Alps, the
Séchilienne slope. Here, we use a combination of major element chemistry
and isotopes ratios (<span class="inline-formula"><sup>87</sup></span>Sr <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M4" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="57ee8123d9c9aefcf23d9c7f6463c158"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="esurf-9-487-2021-ie00001.svg" width="8pt" height="14pt" src="esurf-9-487-2021-ie00001.png"/></svg:svg></span></span> <span class="inline-formula"><sup>86</sup></span>Sr, <span class="inline-formula"><i>δ</i><sup>34</sup></span>S) measured in
different water types of the stable and unstable part of the Séchilienne
instability to assess the contribution of the different lithologies of the
slope and the chemical weathering mechanisms. Chemical and isotopic ratios
are used to characterize weathering processes and the origin of waters and
their flow paths through the massif. A mixing model allows us to allocate the
different major elements to different sources, to identify secondary
carbonate formation as a major process affecting solutes in the subsurface
waters of the instability, and to quantify the involvement of sulfuric and
carbonic acids as a source of protons.</p>
<p>We show that the instability creates favorable and sustained conditions for
the production of sulfuric acid by pyrite oxidation, by opening new
fractures and supplying fresh reactive surfaces. We clearly identify the
contribution of the dissolution of each mineral phase to the chemistry of
the waters, with a clear role of remote gypsum dissolution to the sulfate
budget in the sampled waters. We are also able to refine the preexisting
hydrogeological views on the local water circulation and water flow paths in
the instability by showing the hydrological connectivity of the different
zones. Overall, our results show that the Séchilienne landslide, despite
its role in accelerating rock chemical and physical weathering, acts as a
geological source of CO<span class="inline-formula"><sub>2</sub></span> to the atmosphere. If generalizable to other
large instabilities in mountain ranges, this study illustrates the complex
coupling between physical and chemical erosion and their impact on the
carbon cycle and global climate. The study also highlights the importance of
distinguishing between sulfite oxidation and gypsum dissolution as a source
of sulfate ions to rivers, particularly in mountain ranges.</p> |
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ISSN: | 2196-6311 2196-632X |