Glacier outburst floods and outwash plain development: Skeidararsandur, Iceland

Outwash plains, such as Skeidararsandur, serve as prototypes for braided ri ver facies and analogs for the Mars Pathfinder and Viking 1 landing sites o n the margins of the Chryse Basin. Glacier outburst floods (jkulhlaups) hav e generated some of the largest known terrestrial freshwater flows and rece nt studies suggest that the stratigraphy of outwash plains (sandur) is domi nated by sedimentary sequences laid down during jokulhlaups, rather than by braided river facies produced by an ablation-related flow regime. The mode rn point-source drainage configuration on Skeioararsandur evolved from a di ffuse, multipoint distributary system during glacier retreat, when meltwate r began to be routed parallel to the ice front. The contemporary pattern of water and sediment dispersal across Skeioararsandur differs from the condi tions that prevailed when the ice front was coupled to the sandur, and the November 5-6 1996 outburst flood from Skeidararjokull had little impact on the proximal surface of Skeidararsandur beyond the confines of the entrench ed channels that traverse it, Thus, the point-source dispersal system on Sk eidararsandur may not provide an exact analogue for the pattern of meltwate r dispersal responsible for the sediment assemblage laid down during past j okulhlaups, and caution may be required when comparing conditions on Skeida rarsandur to those presumed to have been experienced during massive outburs t floods elsewhere.