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| Titel |
The chemistry and element fluxes of the July 2011 Múlakvísl and Kaldakvísl glacial floods, Iceland |
| VerfasserIn |
Iwona Galeczka, Eric H. Oelkers, Sigurður R. Gíslason |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250092370
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| Publikation (Nr.) |
 EGU/EGU2014-6707.pdf |
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| Zusammenfassung |
| The glacial floods, called ‘jökulhlaups’, are common in Iceland and are of interest to
geologists for several reasons. Firstly, the heat source origin – subglacial volcanic eruption
or/and subglacial geothermal activity – determines the potential environmental impact of the
floods. For example, if the heat was sourced by a volcanic eruption, acid gas input might lead
to acidic flood waters and toxic metal release from the host rock. In contrast, geothermal
heat melts the ice slowly allowing long-term fluid-rock interaction to neutralize
the flood waters, limiting their toxicity. The chemical composition of the flood
waters is often the only indicator of the flood triggering mechanism in volcanic and
geothermal areas. As such river water chemistry monitoring might be an effective
method to predict an upcoming volcanic eruption. Secondly, glacial floods may
play an important role in global cycle of elements. Due to high discharge during
the events, flood waters can transport large amounts of particulate material. This
particulate material has large surface areas, making it especially reactive once it
arrives in estuaries. Slow dissolution of particulate material releases micro- and
macronutrients which could enhance primary productivity along the coast and in
lakes.
In July 2011, two ~2000 m3/s glacial floods from the Icelandic Mýrdalsjökull and
Vatnajökull glaciers emerged into the Múlakvísl and Kaldakvísl rivers, respectively. 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 river but stabilized at around 1 mmol/kg; a
similar trend was observed in the Kaldakvísl river. Concentrations of most dissolved
elements in the flood waters were comparable to those commonly observed in these rivers.
The concentration of suspended particulate material however, increased dramatically during
the floods and dominated chemical transport during these events. The toxic metal
concentrations were below WHO (World Health Organisation) drinking water limits. 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. Increased concentrations of DOC,
formate, and acetate in the flood waters suggests subglacial microbiological activity
in the melt water prior to the floods. According to PHREEQC modelling, flood
waters were supersaturated with respect to a number of clays, zeolites, carbonates,
and Fe hydroxides. 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
indicates that the heat source for glacier melting was geothermal rather than volcanic. |
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