Emplacement of lava flows on eroded terrain, part I: The case of the Tiretaine valley (Chaîne des Puys, France) - Université Clermont Auvergne Accéder directement au contenu
Article Dans Une Revue Journal of Volcanology and Geothermal Research Année : 2023

Emplacement of lava flows on eroded terrain, part I: The case of the Tiretaine valley (Chaîne des Puys, France)

Résumé

Lava flows often erupt onto eroded landscapes, flowing across plateaus, into valleys and basins, and down escarpments. With the Tiretaine lava flow system in the Chaîne des Puys (Central France), lava flowed over the complex topography of an ancient rift margin. Erupted 41.3 ± 1.3 ka ago onto the granite plateau of the Massif Central, flow initially advanced over a surface that sloped 2°E. On reaching a fault scarp that delimits the plateau, flows descended the 6° slopes of a ravine that cuts the scarp E-W. In part 1 of this work we thus consider the case where lava is emplaced onto relatively flat terrain, then passes over a break-in-slope onto steeper slopes. To do this, we carried out mapping and facies analysis down this ∼6-km-long system, collecting 24 samples on which we completed textural and geochemical analyses. Results reveal three lava facies: (i) a 3 × 2 km proximal zone of inflated pāheohoe with a thickness of 25–50 m; (ii) a channelized medial zone with simple rubble levees nested in the ravine; and (iii) a valley-ponded distal zone with tubes and well-formed columnar jointing. Through simple mass balance calculations, and analogy with systems displaying similar facies, we find that the proximal inflated zone was fed at relatively low (1–5 m3/s) effusion rates. This built the proximal portion of the flow field over a period of 1–6 years, forming a volume of flow-field stored, degassed lava. Failure of the eastern edge of the proximal flow field at the head of the Tiretaine ravine fed high (215–315 m3/s) effusion rate flow down the ravine, to build a channelized flow system in just a few hours. However, the presence of a lava dam at the mouth of the ravine impeded further flow and resulted in ponding. This ponded volume then cooled in-place over a period of 10–11 years. Breaks-in-slope, and the resulting lava–topography interaction, thus created a system of reservoirs and transfers, with different flow rates, dynamics and emplacement time scales. For our case, where the lava flow system is mostly in a UNESCO World Heritage site, the study provides scientific support for Geoheritage efforts, outreach, and initiatives to support protection of geologically important sites. Previous article in issue
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Dates et versions

hal-04107343 , version 1 (26-05-2023)

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Citer

Benjamin Latutrie, Andrew Harris, Benjamin van Wyk de Vries, Lucia Gurioli, Etienne Médard. Emplacement of lava flows on eroded terrain, part I: The case of the Tiretaine valley (Chaîne des Puys, France). Journal of Volcanology and Geothermal Research, 2023, 438, pp.107808. ⟨10.1016/j.jvolgeores.2023.107808⟩. ⟨hal-04107343⟩
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