Ruapehu - IGNS - Science Alert Bulletin V95/38

Wednesday 12 October 1995
0330 hours NZDT (UT +13)
Ruapehu Volcanic Activity

Situation Summary

Ruapehu volcano has experienced a period  of near-continuous moderate
eruptive activity over night.  Raised tremor levels have been recorded on
seismic monitoring equipment by staff at the Institute of Geological &
Nuclear Sciences at Wairakei since approximately 9pm on 11 October.  The
levels of tremor have closely resembled activity during the two peaks of
the eruption to date, on 25 September and 7 October,  but have not been
accompanied by large explosion earthquakes.  Tremor continues at this
elevated level at the time of writing.

New Zealand Army personnel in the Rangipo desert confirmed eruptive
activity associated with these events.   Observations between 9 and 10:30
pm on 11 October revealed a large eruption plume rising to approximately
10 km height and accompanied by ejection of  hot ballistic blocks and
lightning.  The lower portions of the plume were described as a reddish to
orange "geyser-like" feature.

The eruption plume has been tracked,  for 5 hours to date, by the
Meterological Service of New Zealand,  to elevations in excess of 36 000
feet. It has drifted to the northeast to pass over Whakatane and Cape
Runaway.  A feature has been that the plume does not appear to have
detached from the volcano, and the column is presumably being fed by
ongoing weak to moderate activity from Crater Lake basin.

After responding to this event, Institute staff are continuing to maintain
an overnight watch in the seismic laboratory, in case of any sudden change
in the activity,  and will fly over Ruapehu in the morning to record the
effects of the eruption close to the volcano.

Summary and Alert Status

The intensity of volcanic tremor indicates that the present eruption
episode is continuing.  Pending  inspection, we advise that the Alert
Level remains at 3.

BF Houghton  for
Dr CJN Wilson, Programme Leader, Volcanology