{"id":6410,"date":"2020-12-16T11:57:55","date_gmt":"2020-12-16T10:57:55","guid":{"rendered":"https:\/\/dev.asleman.org\/?post_type=60_secondes&p=6410"},"modified":"2020-12-16T11:57:55","modified_gmt":"2020-12-16T10:57:55","slug":"n64-la-coquille-du-leman","status":"publish","type":"60_secondes","link":"https:\/\/asleman.org\/en\/60_secondes\/n64-la-coquille-du-leman\/","title":{"rendered":"No.64: The Lake Geneva shell"},"content":{"rendered":"

\"We others have the lake. It is vast, \ud835\uddf6\ud835\uddf9 \ud835\uddee \ud835\uddf9'\ud835\uddee\ud835\uddf6\ud835\uddff \ud835\uddf1'\ud835\ude02\ud835\uddfb\ud835\uddf2 \ud835\uddfd\ud835\uddf2\ud835\uddff\ud835\uddf9\ud835\uddf2 \ud835\uddee\ud835\ude02 \ud835\uddf3\ud835\uddfc\ud835\uddfb\ud835\uddf1 \ud835\uddf1\ud835\uddf2 \ud835\ude00\ud835\uddee \ud835\uddf0\ud835\uddfc\ud835\uddfe\ud835\ude02\ud835\uddf6\ud835\uddf9\ud835\uddf9\ud835\uddf2. The mountains and hills that border it rise up on all sides...\"<\/p>\n\n\n\n

The words of Charles-Ferdinand Ramuz illustrate a well-known landscape. The morphology of his \"shell\", however, is a little less familiar. Here are the details.<\/p>\n\n\n\n

The history of Lake Geneva is primarily linked to the collision of the Adriatic and Eurasian tectonic plates. This collision raised the Alpine peaks and the folds of the Jura, but also caused the Franco-Swiss plateau to sink. \ud835\uddd6'\ud835\uddf2\ud835\ude00\ud835\ude01 \ud835\uddf9\ud835\uddf2 \ud835\uddf0\ud835\uddee\ud835\ude00 \ud835\uddf1\ud835\ude02 \ud835\udddf\ud835\uddf2\u0301\ud835\uddfa\ud835\uddee\ud835\uddfb \ud835\uddfe\ud835\ude02\ud835\uddf6 \ud835\uddee \ud835\ude03\ud835\uddf2\u0301\ud835\uddf0\ud835\ude02 \ud835\ude02\ud835\uddfb \ud835\uddee\ud835\uddf3\ud835\uddf3\ud835\uddee\ud835\uddf6\ud835\ude00\ud835\ude00\ud835\uddf2\ud835\uddfa\ud835\uddf2\ud835\uddfb\ud835\ude01 linked to the formation of the Pre-Alps.<\/p>\n\n\n\n

The tectonic influence remains marginal in explaining the relief of the Lake Geneva \"shell\". Instead, the scientific literature highlights the role played by glaciers. Thus, it is mainly \ud835\uddf9'\ud835\uddf2\u0301\ud835\uddff\ud835\uddfc\ud835\ude00\ud835\uddf6\ud835\uddfc\ud835\uddfb \ud835\uddf4\ud835\uddf9\ud835\uddee\ud835\uddf0\ud835\uddf6\ud835\uddee\ud835\uddf6\ud835\uddff\ud835\uddf2 \ud835\uddfe\ud835\ude02\ud835\uddf6 \ud835\uddee\ud835\ude02\ud835\uddff\ud835\uddee\ud835\uddf6\ud835\ude01 \ud835\uddf0\ud835\uddff\ud835\uddf2\ud835\ude02\ud835\ude00\ud835\uddf2\u0301 \ud835\uddf9\ud835\uddf2 \ud835\uddf9\ud835\uddee\ud835\uddf0 that is responsible for some of its \ud835\uddfd\ud835\uddee\ud835\uddff\ud835\ude01\ud835\uddf6\ud835\uddf0\ud835\ude02\ud835\uddf9\ud835\uddee\ud835\uddff\ud835\uddf6\ud835\ude01\ud835\uddf2\u0301\ud835\ude00.<\/p>\n\n\n\n

For example, \ud835\uddf9\ud835\uddf2\ud835\ude00 \ud835\uddf4\ud835\uddff\ud835\uddee\ud835\uddfb\ud835\uddf1\ud835\uddf2\ud835\ude00 \ud835\uddf9\ud835\uddf6\ud835\uddf4\ud835\uddfb\ud835\uddf2\ud835\ude00 \ud835\ude07\ud835\uddf2\u0301\ud835\uddef\ud835\uddff\ud835\uddee\ud835\uddfb\ud835\ude01 \ud835\uddf9\ud835\uddf2\ud835\ude00 \ud835\uddf3\ud835\uddfc\ud835\uddfb\ud835\uddf1\ud835\ude00 between the small and large lakes would have been formed by large boulders trapped in the lower glacial layers. The advancing Rh\u00f4ne glacier would have carried these large boulders with it, \"grating\" the bottom of the lake.<\/p>\n\n\n\n

While the Rh\u00f4ne glacier hollowed out the Lake Geneva \"shell\", it also filled it with sediment as it retreated. Today, \ud835\uddf9\ud835\uddf2 \ud835\uddf3\ud835\uddfc\ud835\uddfb\ud835\uddf1 \ud835\uddf1\ud835\ude02 \ud835\uddf9\ud835\uddee\ud835\uddf0 \ud835\uddfd\ud835\uddfc\ud835\ude00\ud835\ude00\ud835\uddf2\u0300\ud835\uddf1\ud835\uddf2 \ud835\ude02\ud835\uddfb\ud835\uddf2 \ud835\uddfd\ud835\uddff\ud835\uddfc\ud835\uddf3\ud835\uddfc\ud835\uddfb\ud835\uddf1\ud835\uddf2\ud835\ude02\ud835\uddff \ud835\uddfa\ud835\uddee\ud835\ude05\ud835\uddf6\ud835\uddfa\ud835\uddee\ud835\uddf9\ud835\uddf2 \ud835\uddf1\ud835\uddf2 \ud835\udfef\ud835\udfec\ud835\udff5\ud835\uddfa, \ud835\ude00\ud835\uddfc\ud835\uddf6\ud835\ude01 \ud835\udff4\ud835\udff2 \ud835\uddf0\ud835\uddfa \ud835\uddf1\ud835\uddf2 \ud835\uddfa\ud835\uddfc\ud835\uddf6\ud835\uddfb\ud835\ude00 \ud835\uddfe\ud835\ude02'\ud835\uddf6\ud835\uddf9 \ud835\ude06 \ud835\uddee \ud835\udfed\ud835\udfee\ud835\udff1 \ud835\uddee\ud835\uddfb\ud835\ude00. This loss of depth is explained by the deposition of sediments carried by the tributaries of Lake Geneva.<\/p>\n\n\n\n

Other more specific remains can be explained by a combination of factors. For example, \ud835\uddf9\ud835\uddf2 \ud835\uddff\ud835\uddf2\ud835\uddf9\ud835\uddf6\ud835\uddf2\ud835\uddf3 \ud835\uddf6\ud835\uddfa\ud835\uddfa\ud835\uddf2\ud835\uddff\ud835\uddf4\ud835\uddf2\u0301 \ud835\uddf1\ud835\ude02 \ud835\udddb\ud835\uddee\ud835\ude02\ud835\ude01-\ud835\udde0\ud835\uddfc\ud835\uddfb\ud835\ude01 between Corsier and Versoix is a former mound of uneroded molasse on which a significant layer of sediment has been deposited. In another case, \ud835\uddf9\ud835\uddf2\ud835\ude00 \ud835\uddf3\ud835\uddf6\ud835\uddfb\ud835\uddf2\ud835\ude00 \ud835\uddf0\ud835\uddfc\ud835\uddf9\ud835\uddf9\ud835\uddf6\ud835\uddfb\ud835\uddf2\ud835\ude00 \ud835\ude00\ud835\uddfc\ud835\ude02\ud835\ude00-\ud835\uddf9\ud835\uddee\ud835\uddf0\ud835\ude02\ud835\ude00\ud835\ude01\ud835\uddff\ud835\uddf2\ud835\ude00 off Coppet are former glacial tunnels, filled in during deglaciation.<\/p>\n\n\n\n

If you'd like to find out more anecdotes about the morphology of Lake Geneva, visit our website to (re)discover the glacial origin of \ud835\uddfd\ud835\uddf6\ud835\uddf2\ud835\uddff\ud835\uddff\ud835\uddf2\ud835\ude00 \ud835\uddf1\ud835\ude02 \ud835\udde1\ud835\uddf6\ud835\ude01\ud835\uddfc\ud835\uddfb in Geneva (60s n\u00b0 44<\/a>), the formation of \ud835\uddff\ud835\uddee\ud835\ude03\ud835\uddf6\ud835\uddfb\ud835\ude00 \ud835\ude00\ud835\uddfc\ud835\ude02\ud835\ude00-\ud835\uddf9\ud835\uddee\ud835\uddf0\ud835\ude02\ud835\ude00\ud835\ude01\ud835\uddff\ud835\uddf2\ud835\ude00 at the mouth of the Rh\u00f4ne (60s n\u00b0 61<\/a>) or another version of the appearance of Lake Geneva mixing the \ud835\uddf4\ud835\uddf2\u0301\ud835\uddee\ud835\uddfb\ud835\ude01 \ud835\uddda\ud835\uddee\ud835\uddff\ud835\uddf4\ud835\uddee\ud835\uddfb\ud835\ude01\ud835\ude02\ud835\uddee (60s n\u00b0 16<\/a>).<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

Photo credits :<\/p>\n\n\n\n

\"\ud83d\udcf8\" Swisstopo
\"\ud83d\udcf8\" Jean-Louis Lods<\/p>\n\n\n\n

Sources : <\/p>\n\n\n\n

- Girardclos, Corboud, Wildi (2015)<\/a>Limno-geological cruise on Lake Geneva: geological history of the Lake Geneva basin and human occupation\". University of Geneva (online)
- J.F. Ramuz, Diary, 1902, in L\u00e9maniques n\u00b0100<\/a>
- Le Temps (2016)<\/a>, The mysteries revealed at the bottom of Lake Geneva\u201c.\u201d<\/p>\n\n\n\n

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