LARGE-SCALE ICE-VOLCANO INTERACTION: POSSIBLE EFFECTS OF LARGE SILICIC CALDERA-FORMING ERUPTIONS AND SUPERPLUME EVENTS UNDER ICE SHEETS

The greatest known volcanic events on Earth are eruptions associated with the formation of large ash-flow calderas and superplume events when large igneous provinces (LIPs) are formed. The large ash-flow calderas are found in continents and island arcs while LIPs occur in a variety of tectonic settings.  Ice sheets have covered parts of continents at various times in Earth’s history and have been postulated for Mars.  However, no known examples of large ash-flow calderas or LIPs formed within ice sheets have been reported.  This may be because such events have not occurred or that the remains of such events have subsequently been removed by erosion or covered by later volcanism.  Characteristics of present-day subglacial volcanic activity, evidence from the geological record and simple physical models can be used to explore the possible effects of large volcanic events under ice.  It is found that a silicic eruption with a magma discharge rate of 10⁹ kg s^-1 would melt its way through a 3000 m thick ice sheet in hours or days.  If the volume of magma erupted is of the order of 1000 km³, apparently only a minor part is emplaced subglacially.  The major part would be erupted into the atmosphere, suggesting that climatic loading of aerosols and tephra would not be much affected by the ice cover.   An eruption of this magnitude should lead to melting of up to hundreds of km³ of ice and massive jökulhlaups.  The average magma supply rate during superplume events is of the order of 1 km³/yr (~10⁶ km³ erupted over ~10⁶ years).  If the magma is erupted in frequent large-volume eruptions (100-1000 km³) with effusion rates of ~10 km³/yr, it is to be expected that each eruption would create a large tuya within the ice sheet.  Such eruptions could create up to thousands of km³ of meltwater and lead to very large jökulhlaups.  Assuming a LIP area of 10⁶ km² and enhanced heat flow corresponding to solidification and cooling of 1 km³/yr of magma, it is found that the resulting basal melting is an order of magnitude less than the present-day surface accumulation in Antarctica or Greenland.  Thus, it is likely that a large polar ice sheet would survive the enhanced basal melting associated with a superplume event and significantly reduce its interaction with the atmosphere.