Processus et rythmes de l’incision des sandar proximaux postérieure au petit âge glaciaire (sud de l’Islande)

• Published in: Géomorphologie : relief, processus, environnement
• Main Authors: Roussel, Erwan, Chenet, Marie, Grancher, Delphine, Jomelli, Vincent
• Format: Article in Journal/Newspaper
• Language: French
• Published: Groupe français de géomorphologie 2009
• Subjects: ajustement fluvial; Islande; lichénométrie; paraglaciaire; petit âge glaciaire; recul glaciaire; sandur; fluvial adjustment; glacial retreat; Iceland; lichenometry; little ice age; paraglacial; geo; envir; Sandar; glacier
• Online Access: https://doi.org/10.4000/geomorphologie.7416; http://journals.openedition.org/geomorphologie/7416

Since the end of the Little Ice Age, glacial outlets of southern Iceland have undergone a substantial retreat, which has modified hydrological and sedimentological settings and caused fluvial adjustments. Based on lichenometric dating and topographical measurements, this study demonstrates that proximal sandar adjustment to glacier retreat follows two distinctive stages. The first one can be regarded as the reaction time of the sandur, during which the incision of the outwash plain is inhibited due to glacier front stagnation or paraglacial sediment release, which maintains the marginal sediment budget in a stable state. The second stage is characterized by the proximal sandur incision, which is triggered from the moment when the paraglacial sediment supply is insufficient to keep the sandar stable. During the second stage, the proximal sandur incision rate decreases as the glacier front retreats. The effect of glacier front readvances on the rate of proximal sandur incision is discussed. We found that glacier readvances could be able to slow down the proximal sandur incision, without time lag, by enhancing the marginal sedimentary stock. Depuis la fin du petit âge glaciaire, les langues glaciaires sud-islandaises ont enregistré un recul prononcé qui modifie a priori les conditions hydrosédimentaires offertes aux cours d’eau proglaciaires. À partir de datations lichénométriques et de mesures topographiques, cette étude montre que l’ajustement des sandar proximaux au recul glaciaire s’effectue en deux phases. La première correspond au temps de réponse du sandur, durant lequel l’incision de la plaine fluvio-glaciaire proximale est empêchée soit par la stagnation du front glaciaire soit par un apport de sédiments d’origine paraglaciaire. La seconde correspond au déclenchement de l’incision du sandur proximal lorsque l’apport de sédiments paraglaciaires n’est plus suffisant pour maintenir la plaine fluvio-glaciaire dans un état stable. Lors de cette seconde phase, la vitesse d’incision du sandur proximal a ...