The origin and evolution of Holocene sandur deposits in areas of jokulhlaup drainage, Iceland

Abstract

The impact of jokulhlaup (flood) history on the origin and evolution of the coastal sandar of southern Iceland is explored in this paper through analysis of the morphology, sedimentology and stratigraphy of six different sandur environments. The results indicate that three distinct models of sandur evolution can be identified from the landform and lithofacies assemblages of the deposits. Type I sandur deposits are characterized by repeated, thin, upward-fining cycles of gravels, sands and silts, and are found in areas of seasonal meltwater activity associated with braided river systems. Type II sandur deposits are characterized by thick (>10 cm), coarsening-upward, clast-supported cobble gravels, overlain by a fining-upward sequence of fine gravels, sands and silts, which are found in areas of prolonged (days and weeks), high magnitude drainage events associated with subglacial geothermal activity or ice-dammed lake drainage. Finally Type III sandur deposits are typified by thick sequences (8m+) of structureless pumice granules, underlain by a crudely bedded basal unit, and capped by several metres of trough cross-bedded and horizontally bedded granules. These deposits are associated with catastrophic drainage events generated by subglacial volcanic eruptions. -from Author