Volatile concentrations in basaltic tuyas, edifices that form during a subglacial eruption and remain once the ice sheet has retreated, have been used to calculate the thickness of the overlying ice sheet at the onset of the eruption (Tuffen, 2010). However, subglacial eruptions are complex events and this technique does not always provide a clear answer (Schopka et al., 2006; Edwards et al., 2009). The purpose of this research is to evaluate this technique and investigate constraints on the quality of data collected by attempting to calculate the minimum ice thickness under which Hlöðufell, a tuya in south-central Iceland, erupted.
Hlöðufell is a Holocene tuya located in the Western Rift Zone of Iceland, 9 km south from the modern edge of Langjökull ice cap. Dissolved H2O concentrations were measured using Fourier transform infrared spectroscopy (FTIR) and quenching pressures were calculated using the VolatileCalc pressure-solubility model (Newman and Lowenstern, 2002). Overlying ice thickness was calculated by relating quenching pressures, the density of ice, and the elevation of the sample.
Water concentrations range from 0.068 –to 0.478 wt. % H2O, representing pressures ranging from 0.66 to 24.72 bars. These pressures represent ice thicknesses between 0 and 268 m thick. The minimum ice thickness level is represented in the lithofacies of the tuya by the passage zone, the transition between subaerial and subaqueous flows. The minimum ice thickness for Hlöðufell is ~ 500 m, much thicker than this study calculated using water concentrations. This indicates that the volatile concentrations in the basaltic glasses at Hlöðufell do not record the accurate quenching pressure. We interpret the overall low water concentrations to mean that our samples must have degassed at or close to atmospheric pressures at higher elevations, and flowed downslope into areas of thicker ice or deeper melt-water before quenching. These results show that subglacial eruptions and degassing processes are complex and variable and require further investigation.
| Identifer | oai:union.ndltd.org:UMASS/oai:scholarworks.umass.edu:masters_theses_2-1488 |
| Date | 24 March 2017 |
| Creators | Lee, Carver |
| Publisher | ScholarWorks@UMass Amherst |
| Source Sets | University of Massachusetts, Amherst |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Masters Theses |
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