Today’s stage takes us from La Mure on the Drac River, past Bourg d’Oisans, the site of the lake that burst to flood Grenoble in 1219, up the Arc River, over the Col du Télégraphe and then up the valley of La Valloirette to the col du Galibier before descending down the valley of the Guisane to finish in Serre-Chevalier. If we had gone north instead of east out of La Mure we would have run into the Laffrey lakes, a quartet of glacial lakes.
The four lakes, from the south end of the valley near La Mure to the head at the north, are Pierre-Châtel, Pétichet, the grand lac de Laffrey, and Mort. Each one is dammed by a moraine left by the local glacier as it receded up the valley some 11,000 years ago.
Situated as they are in a tectonically active area, it is possible to reconstruct the history of earthquakes in the region using the sediments on the bottoms of the lakes (Nomade et al. 2005). Mixing of the sediment in Pétichet and Pierre-Châtel by animals makes them less useful for paleoseismology than the grand lac de Laffrey, though.
A great stage win for Primož Roglič on the Galibier. It will probably be overshadowed, perhaps, by the drama of the general classification and the green jersey this year, but like the similarly dramatic stage to Mont Ventoux last year, it will go down in my books as a stage which Serge Pauwels almost won.
- Nomade et al. (2005). Reconstructing historical seismicity from lake sediments (Lake Laffrey, Western Alps, France). Terra Nova. http://dx.doi.org/10.1111/j.1365-3121.2005.00620.x