Ruapehu - IGNS - Science Alert Bulletin V95/22

29 September 1995
19.00 hours
Ruapehu Crater Lake

Situation Summary

As of 19.00h the following new information is available.

*    To 1200h today  the level of volcanic tremor was lower, but still
elevated above pre-eruption levels.  Since 1200h today the tremor level
has risen again and remains high at this time.

*    Several discrete volcanic earthquakes have occurred since 1200h,
coincident with the increase in volcanic tremor at that time. Several
eruption plumes have been reported.

*    Institute staff were able to conduct an overflight late this
afternoon, unfortunately conditions were not favourable for observations.
No major changes  were reported.

*    Institute staff are maintaining the 24hr watch on seismicity, and
completed a ground deformation survey this evening.

*    The results of a size analysis of the ash (collected 16km from Crater
Lake) shows that 25% of the ash is finer than 12 microns and 10% less than
3 microns.

Under pinning research;

A team of GNS seismologists from Wellington have installed 9 portable
seismographs around the volcano, so that more data can be collected to
further our understanding of the processes operating at depth bellow the
volcano. Data obtained on wednesday included 14 of these events.

Other Institute scientist are currently analysing ash, leachate and scoria
samples collected  in the last few days.

Plans are being formulated for wider deformation studies of the flanks of
Ruapehu using  Electronic distance measuring equipment.

Conclusions and Alert status

Due to the increase in seismicity this afternoon the Alert Level for
Ruapehu remains at Level 4.

BJ Scott for;
Dr C J N Wilson, Programme Leader, Volcanology.