Glacier outburst floods and outwash plain development: Skeiäarársandur, Iceland

Abstract

Outwash plains, such as Skeiaararsandur, serve as prototypes for braided river facies and analogs for the Mars Pathfinder and Viking 1 landing sites on the margins of the Chryse Basin. Glacier outburst floods (jokulhlaups) have generated some of the largest known terrestrial freshwater flows and recent studies suggest that the stratigraphy of outwash plains (sandur) is dominated by sedimentary sequences laid down during jokulhlaups, rather than by braided river facies produced by an ablation-related flow regime. The modern point-source drainage configuration on Skeiaararsandur evolved from a diffuse, multipoint distributary system during glacier retreat, when meltwater began to be routed parallel to the ice front. The contemporary pattern of water and sediment dispersal across Skeiaararsandur differs from the conditions that prevailed when the ice front was coupled to the sandur, and the November 5–6 1996 outburst flood from Skeiaararjokull had little impact on the proximal surface of Skeiaararsandur beyond the confines of the entrenched channels that traverse it. Thus, the point-source dispersal system on Skeiaararsandur may not provide an exact analogue for the pattern of meltwater dispersal responsible for the sediment assemblage laid down during past jokulhlaups, and caution may be required when comparing conditions on Skeiaararsandur to those presumed to have been experienced during massive outburst floods elsewhere.