Geophysical reconstruction of the late Holocene proximal proglacial landsystem at Skeiðarársandur, southeast Iceland

Abstract

Sandur plains are extensive sedimentary bodies formed in proglacial settings by glaciofluvial processes. Icelandic sandar have been hypothesised to be comprised of thick alluvial successions that provide critical insight into the processes that contributed to their formation and evolution. However, to-date, most sandar research has focused on the analysis of sedimentary successions associated to topographically-confined and small-scale systems. These, however, do not capture the variety or scale of processes that influence sandar architecture. Therefore, detailed subsurface analysis of large-scale and unconfined sandar is vital to understand how these systems respond to fundamental drivers, such as: (i) glacier oscillations, and (ii) episodic sediment flux from glacier outburst floods (aka. jökulhlaups). We report an extensive, low-frequency (40 & 100 MHz) ground-penetrating radar (GPR) survey of the ice-proximal component of a large-scale (~13km2) active sandur in southeast Iceland. A bright and continuous reflection (PR1) is identified within all radargrams and provides a boundary between pre-LIA and LIA to present-day sedimentation. GPR data reveals a ~50 m thick ice-proximal sediment wedge that is attributed to jökulhlaup and surge-related glaciofluvial activity during the Little Ice Age (LIA). An approximate rate of deposition of 0.2–0.65 m a-1 has been calculated for the sediment wedge above PR1. Furthermore, we propose an extensive, sandur-wide, pre-LIA ice marginal limit of Skeiðarárökull, southeast Iceland, based on observations reported here and in previous work.