Oct 3 1996, 3:00 pm - Ruapehu Volcano

Activity at Ruapehu volcano has been at a low level for some weeks now and a detailed evaluation of the surveillance data available at this time indicates that the Alert Level should be lowered from Level 2 to Level 1.

Although several of the parameters that we record and use to make an evaluation of the status of the volcano remain at higher levels than they were before the enhancement of activity in June 1996 they have all been at uniform levels for some time. At present, these levels are now defining the current 'background state' for Ruapehu, and in effect the baseline has been moved. In terms of the Scientific Alert Levels this justifies moving the level from 2 down to 1.

Minor ash eruptions occurred on September 1 - 2 and possibly again on September 9. These were minor, although the September 2 - 3 activity was enough to close down one of the ski fields. Since September 9 no ash emissions have been reported and seismic activity has been at relatively low levels, except on September 29 when a short-lived period of volcanic tremor was recorded, no eruptive activity followed. Two small ponds are now forming on the floor of the crater that was active in 1996, the higher pool is overflowing into the lower one. A recent COSPEC measurement shows an output of 1700 tons/day SO₂, significantly down from the previous measurement of 5500 tons/day.

Mt. Ruapehu continues to be an active volcano and this change in Alert Status must not be interpreted to mean that there is no further possibility of eruptions. The current eruptive episode appears to have ended, but some hazardous areas remain on the volcano. Isolated explosive eruptions could still occur without useful warning signs and the active crater area should continue to be treated with respect.

B.J. Scott (for C.J.N. Wilson)
Volcanology Programme Leader