Subglacial explosive volcanism generates hazards resulting from magma-ice interaction, including meltwater flooding and fine-grained volcanic ash. The literature contains descriptions of some recent subglacial eruptions and suggests several heat transfer mechanisms but lacks a detailed study of heat transfer in the magma-water-ice system. Quantification of heat transfer processes allows further development of dynamic models of subglacial eruptions that may help to inform hazard management. 1 have quantified particle-water heat transfer with a model that couples intraparticle conduction with boiling on particle surfaces. In general, where magma is fragmented by explosion or granulation, much of the initial heat of the magma is transferred to water rapidly compared to eruption timescales. Within liquid-dominated subglacial eruption cavities, heat fluxes from water to ice of c. 0.6 MW m-2 can be obtained by single phase free convection. When local boiling occurs in the vent region heat fluxes of 3-5 MW m-2 , approaching those inferred for some recent subglacial eruptions, may be attained by two-phase free convection and may be increased by momentum transfer from the eruption jet. In vapour-dominated cavities, heat fluxes of 0.1-1 MW m-2 can be obtained by steam condensation during free convection, depending on cavity pressure and the concentration of non-condensable gases present. Forced convection reduces the effect of non-condensable gases; in this case a maximum heat flux of c. 2 MW m-2 may be attained. In a drained and depressurised cavity the resulting eruption jet may transfer heat by a combination of radiation, steam condensation and pyroclast impact. Heat fluxes from radiation and condensation are unlikely to exceed 0.5 MW m-2. An experimental study of pyroclast impact on ice, using sand at 300 °C, demonstrated heat fluxes of 0.4 MW in-2. The effects of higher particle temperature and damage from repeated impact of larger particles remain to be investigated.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:730248 |
| Date | January 2016 |
| Creators | Woodcock, Duncan Charles |
| Publisher | Lancaster University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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