Glacier drainage and sandur formation at Kötlujökull, South Iceland

Abstract

Over a number of years research on a stretch of the southeastern glacier margin of Kötlujokull in South Iceland, 8 km in length, has focused on correlating the manner of glacier drainage with the genesis of sandar, exemplified by the recent evolution of the glacier foreland. The research has yielded the following results. During an initial period, beginning prior to 1945 and ending between 1966 and 1975, a belt of moraines about 1 km wide was destroyed in stages, except for a few remnants, by 11 outbreaks of subglacial meltwater at different times and locations along the glacier front. These outbursts were associated with the genesis of “ordinary”; sandar, which are referred to here as “low sandar.”; The main evolution of these sandar, and especially of their proximal parts, took only a few days and was correlated with a discharge of meltwater under high hydrostatic pressure from a subglacial tunnel mouth. The details of such an outburst are described. Prior to 1975 a general change occurred from the subglacial drainage which had prevailed earlier to predominantly supraglacial drainage. After 1978 only one subglacial meltwater exit remained, at the western corner of the glacier. The increasing violence of the supraglacial drainage was perhaps caused by structural changes in the glacier. During this second period this supraglacial drainage gave rise to the formation of a belt of finegrained sandar which largely covered the “low sandar”; and hence are called “high sandar.”; In contrast to the subglacial drainage the supraglacial drainage has not led to any serious destruction of the moraines. “Low”; and “high”; sandar differ in their sedimentological genesis. The high sandar in front of Kötlujökull are fan‐shaped bodies of sand, corresponding to a special model of facies. This evolution occurred partly under conditions of a high flow regime, and with continuous formation of antidunes.