The chemistry and element fluxes of the July 2011 Múlakvísl and Kaldakvísl glacial floods, Iceland

This study describes the chemical composition and fluxes of two ~2000 m3/s glacial floods which emerged from

the IcelandicMýrdalsjökull and Vatnajökull glaciers into the Múlakvísl and Kaldakvísl rivers in July 2011.Water

samples collected during both floods had neutral to alkaline pH and conductivity from 100 to 900 μS/cm. The

total dissolved inorganic carbon (DIC), present mostly as HCO3

−, was ~9 mmol/kg during the flood peak in the

Múlakvísl but stabilized at around 1 mmol/kg; a similar behaviour was observed in the Kaldakvísl. Up to

1.5 μmol/kg of H2S was detected. Concentrations of most of the dissolved constituents in the flood waters

were comparable to those commonly observed in these rivers. In contrast, the particulate suspended material

concentration increased dramatically during the floods and dominated chemical transport during these events.

Waters were supersaturated with respect to a number of clays, zeolites, carbonates, and Fe hydroxides. The

most soluble elements were Na, Ca, K, Sr, Mn, and Mg, whereas the least soluble were Ti, Al, and REE. This

is consistent with the compositions of typical surface waters in basaltic terrains and the compositions of

global rivers in general. The toxic metal concentrations were below drinking water limits, suggesting

that there was no detrimental effect of flood waters chemistry on the environment. Increased concentration

of DOC, formate, and acetate in the flood waters suggests substantial subglacialmicrobiological activity

in the melt water prior to the floods. Reaction path modelling of the flood water chemical evolution

suggests that it experienced subglacial water–rock interaction for at least a year in the presence of limited

amounts of acid gases (e.g. SO2, HCl and HF). This suggests that the heat source for glaciermeltingwas geothermal

rather than volcanic.