Deception Island, Antarctica (1969) Given that subglacial eruptions occur in often sparsely populated regions, they are not commonly observed or monitored; thus timings and sequences of events for an eruption of this type are poorly constrained. Research of the 1969
Deception Island eruption demonstrates that the impact of a subglacial eruption is not limited purely by
glacier thickness, but that the pre-volcanic ice structure and densification (proportion of impermeable ice) play a role as well. In this case, even though the glacier was thin, a large
jökulhlaup was observed as the glacier was largely made up of impermeable (unfractured) ice with a sudden
supraglacial flood once the cavity has reached capacity. The resulting flood severely damaged buildings on the island, with complete destruction of a British scientific station.
Grímsvötn, Iceland (1996) Over a period of 13 days in 1996, 3 km2 of ice was melted with erupted magma fracturing into glass to form a 7 km long and 300 m high
hyaloclastite ridge under 750 m of ice at Gjalp
fissure vent of
Grímsvötn volcano in Iceland. Meltwater flowed along a narrow basal glacier bed into a
subglacial lake for five weeks, before being released as a sudden flood, or
jökulhlaup. Although it has been proposed that subglacial volcanism may play a role in the dynamics of
West Antarctic ice streams by supplying water to their base, for the Gjalp eruption, no rapid basal sliding was observed at the regional scale, with the formation of ice cauldrons over eruptive fissures due to the sudden removal of mass at the base. Research demonstrated that for warm-based glaciers, the effects of subglacial volcanic eruptions are localised, with eruptions forming deep depressions and causing jökulhlaups. For there to be significant changes in the extent and shape of an
ice sheet, extensive subglacial volcanism would be required, melting a considerable fraction of the total ice volume over a short period of time.
Eyjafjallajökull, Iceland (2010) , Iceland, in 2010 In the first two days of the eruption, ice cauldrons were formed over the volcanic vents. Radar images reveal the development of these cauldrons in a 200 m thick ice cover within the summit
caldera. They can also be used to document the
subglacial and
supraglacial passage of meltwater away from the eruption site. Research shows the eruption breached the ice surface four hours after the initial eruption onset, whilst meltwater release was characterised by accumulation and subsequent drainage, with most of the volcanic material in the ice cauldrons being drained in hyperconcentrated floods. ==See also==