Hydrogeological implications of glacial landscape evolution at Skeiðarársandur, SE Iceland

Patterns of groundwater recharge and flow in present day and palaeo-glacial environments are governed by both geomorphology and subsurface sedimentology. This paper assesses the hydrogeological implications of glacial landscape evolution and develops a conceptual model of glacial landscape evolution and hydrogeological interaction. The ice-marginal zone of Skeiðarársandur, SE Iceland was selected as a case study of a temperate, actively-receding glacier landsystem that is affected by both surging behaviour and periodic glacier outburst floods (jökulhlaups). The groundwater table elevation was measured approximately every 2-5 days throughout two six-week summer field seasons in 2000 and 2001, and once in March 2001, using a network of shallow piezometers, and hydraulic conductivity was calculated based on grain-size distribution analysis of sampled aquifer materials. The hydraulic conductivity of the near surface aquifer at the study site spans three orders of magnitude and is highest and most varied in areas inundated by the November 1996 jökulhlaup. The shallow water table in the study area responds dynamically to precipitation events with the greatest fluctuation in an enclosed moraine lake basin with a perched aquifer underlain by ice and in a zone of outwash fans proximal to the ice margin. The seasonal decline in water table is greatest at the ice margin, reflecting the reduced winter recharge from the stagnant ice zone. Landsystems with morainic relief are associated with localised moraine/precipitation-fed groundwater systems. These localised groundwater systems are superimposed on the intermediate/regional scale groundwater systems that discharge further down sandur and offshore and are dominated by the gently-sloping geomorphologically-uniform outwash plain. Groundwater-fed lakes, formed in depressions from ice blocks deposited during jökulhlaups, may provide important ecological niches. The investigations at this site demonstrate that glacial outburst floods and glacier margin fluctuations produce a suite of sediments, landforms and environments that affect the hydrogeological system.