Ruapehu - IGNS - Science Alert Bulletin V95/29

Tuesday 3 October 1995
18.30 hours NZDT (UT +13)
Ruapehu Volcanic Activity 

Situation Summary

As of 18.30 hours the situation is:

*     Volcanic seismicity has remained at a low level (at or below
pre-eruption levels) since the last Science Alert Bulletin at 20.00
yesterday.  Volcanic tremor has been recorded fairly continuously, but has
remained at low levels. Discrete volcanic earthquakes have been recorded
at about 12.40 and 18.18 hours today, the latter accompanied by a distinct
plume emission event.

*     Steam-rich plumes rising to heights of 1-6 km have been seen above
the volcano for much of today.  With one exception at 18.18, the
explosions feeding these plumes are so small that they are not recorded as
volcanic earthquakes.  During the morning, the plumes carried up some ash,
which was deposited to the north as a dusting over the Whakapapa area as
far as the Top of the Bruce road.  Ash was also reported in the form of
'dirty' hail and rain as far as the Chateau.  Through the afternoon, the
plumes contained little or no ash.

*     Taking advantage of good weather, Institute field parties have
worked on the eastern, southern and northern flanks of the volcano.  On
the eastern side, one party studied the way in which ash fall material is
being eroded as the snow on which it was deposited melts.  On the western
side, two parties measured and sampled the September 23 lahar deposits in
the Whakapapaiti area.  Another party undertook further deformation
monitoring in the Whakapapa and Turoa areas, while a COSPEC flight to
measure SO2 levels in the plume was successful.  Available results will be
issued in tomorrow's Science Alert Bulletin.

Conclusions and Alert status

Seismic information and eyewitness report indicate the volcano is
sustaining a mild level of eruptive activity.  We thus advise that the
Alert Level for Ruapehu remains Level 3.

Dr C J N Wilson, Programme Leader, Volcanology. 
Ph: (07) 374 8211; Fax (07) 374 8199