Vallées glaciaires et fjords : réflexions à partir de l’exemple islandais

Glaciations generate glaciers, it is obvious. But the latter are not identical, they vary according to their mass, their position on the topography (summit or not), the temperature of their ice, their flows and… time. Glacial actions are therefore extremely varied and leave numerous traces, which allows geomorphologists to reconstruct the evolution of the landscapes that they have affected. Among the traces we will note the fjords. These ancient glacial valleys invaded by the rising sea are particularly spectacular because of their youth and the landscapes they generate (high sub-vertical walls, waterfalls, shoulders, hanging valleys, wild aspect, etc.) which attract tourists and cruise passengers. The best known, real geomorphological prototypes are the Norwegian fjords. But there are many other countries with fjords (Greenland, Alaska, Chilean Patagonia, South Island of New Zealand, etc.) which host notable differences, beyond their common characteristics. Among the latter, the fjords of Iceland offer unusual characteristics: exceptional widths, relatively shallow entrenchment (rarity of overdigging) and above all numerous sedimentary deposits downstream going so far as to form lidos. The aim of this article is to recapitulate the knowledge in terms of glacial geomorphology and to show the particularism of the Icelandic fjords. Finally, explanatory hypotheses of the latter are put forward, supported by photographs.