Jul 28 1997, 10:30 am - Ruapehu Volcano

Over the weekend volcanic tremor recommenced at Mt. Ruapehu, the first significant tremor since August 1996.

The tremor started gradually on Saturday morning (July 26) at about 03:30 NZST and quickly increased in vigour to reach a maximum by 05:30. This tremor was sustained until 10:30 on Sunday (July 27), at a level of more than twice the typical background level at Ruapehu.

A further weaker period of tremor was recorded on Monday (July 28) from 02:20 to 05:10.

The 1996 eruptions were preceded by strong volcanic tremor on June 15, about 36 hours before eruptive activity started. The tremor recorded this weekend is of lower amplitude than that recorded before the 1996 eruptions, but has been sustained for a longer period than in 1996 (31 hours versus 11 hours in 1996).

The occurrence of this volcanic tremor increases the likelihood of further eruptive activity at Ruapehu in the short term, ie. days to weeks.

This level of activity is insufficient to justify a change in the alert level for the volcano, as an increase to Level 2 would require the actual onset of eruptive activity.

The Alert Level remains at 1.

B.J. Scott (for C.P. Wood)
Volcanology Section Leader