Ruapehu - IGNS - Science Alert Bulletin V95/51

Saturday 21 October 1995
1600 hours NZDT (UT +13)
Ruapehu Volcanic Activity

Situation Summary

As of 1600 hours, the following information is available.

*     A further successful COSPEC flight, to measure the SO2 gas output
from Ruapehu was made yesterday afternoon by Dr BW Christenson.  The
flight also obtained excellent views into the active crater area and
recorded what appears to be the first signs of lava dome growth on the
crater floor.  If this observation is correct it is consistent with the
seismicity reported below.

*     Over all seismicity levels have remained low at Ruapehu since the
last bulletin at 1000 h on 20 October.  The number of degassing eruption
type events (without sudden onsets) has declined in size and frequency
since about 0100h on 19 October.  There has been no volcanic tremor in the
last 24hrs, however the record from Dome has become dominated by small (M
1-2) volcano tectonic earthquakes. These would indicate some form of
brittle failure and may represent some form of intrusion at shallow
(1-2km) depth.

*     A brown gas plume continues to be emitted from Ruapehu.  Earlier
today an Eagle Air flight reported ash on the aircraft after landing at
Palmerston North. No distinct ash rich eruptions have been reported.

*     The SO2 discharge remains high. 

(SO2 is a toxic gas which could produce a significant gas hazard on the
upper slopes of Ruapehu, and possibly beyond, in suitable wind
conditions.)

Conclusions and Alert Status

The present eruption episode is continuing at a reduced level, with weak
ash but strong gas emissions.  We  advise that the Alert Level remains at
3 for Ruapehu volcano.

BJ Scott  for 
Dr CJN Wilson, Programme Leader, Volcanology