Depuis la fin du petit age glaciaire, les langues glaciaires sud-islandaises ont enregistre un recul prononce qui modifie a priori les conditions hydrosedimentaires offertes aux cours d'eau proglaciaires. A partir de datations lichenometriques et de mesures topographiques, cette etude montre que l'ajustement des sandar proximaux au recul glaciaire s'effectue en deux phases. La premiere correspond au temps de reponse du sandur, durant lequel l'incision de la plaine fluvio-glaciaire proximale est empechee soit par la stagnation du front glaciaire soit par un apport de sediments d'origine paraglaciaire. La seconde correspond au declenchement de l'incision du sandur proximal lorsque l'apport de sediments paraglaciaires n'est plus suffisant pour maintenir la plaine fluvio-glaciaire dans un etat stable. Lors de cette seconde phase, la vitesse d'incision du sandur proximal a tendance a ralentir au fur et a mesure que le front du glacier recule. La question de l'impact des re-avancees glaciaires sur la vitesse d'incision du sandur proximal est posee. En realimentant le stock sedimentaire de la marge proglaciaire, les re-avancees glaciaires seraient en mesure de provoquer un ralentissement quasiment immediat de l'incision du sandur proximal. 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.