Mar 24 2006, 2:00 pm - Raoul Island Volcano

Image courtesy of the OMI SO₂ group at the University of Maryland and NASA / KNMI / FMI.

Sulphur dioxide (SO₂) gas was detected by a satellite about 5 hours after the Raoul Island eruption on Friday 17 March. SO₂ data were supplied by the OMI SO₂ group at the University of Maryland and NASA / KNMI / FMI. The total amount of SO₂ released during the eruption and the subsequent 5 hours was estimated at 200 tonnes. While this is a relatively small amount of SO₂, it is significant in that it confirms the involvement of magmatic gases in the eruption, and the presence of degassing magma within the volcano. Subsequent observations have not detected further SO₂ discharge, most likely owing to absorption of this gas by the vent/lake hydrothermal system.

Over the last few days the level of earthquake activity at or close to Raoul Island has continued to decline and is now only 5 to 10 earthquakes per day, most of which are probably too small to be felt on the island.

The likelihood of future magmatic activity is considered to be higher than originally thought, now that magmatic gas involvement has been confirmed. The lack of any unequivocal seismic evidence for magma movement (such as the strong volcanic tremor observed before the 1964 eruption) suggests that the volume of magma at shallow depth beneath Raoul Island may be relatively small, and the decline in seismic activity since the eruption suggests that at this stage further magma may not moving to shallow depth. Careful seismic monitoring of Raoul Island will continue.

The Alert Level for Raoul Island remains at Alert Level 2.

Steve Sherburn
GeoHazards Duty Officer