Ruapehu - IGNS - Science Alert Bulletin V95/49

Thursday 19 October 1995
1700 hours NZDT (UT +13)
Ruapehu Volcanic Activity

Situation Summary

As of 1700 hours, the following information is available.

*     Tremor levels have remained low at Ruapehu during the last 24 hours,
although numerous degassing eruption type events (without sudden onsets)
have been recorded by the Dome (summit) seismograph, along with a few long
period earthquakes (as described in V95/48) best recorded on the Chateau
instrument.  Field parties have observed moderate ash eruptions from the
southern vent in Ruapehu crater, at times which correlate with Dome
seismic events.  At other times, a voluminous gas plume was emitted from
the northern vent.

*     GNS parties have gone into the field to carry out tilt level surveys
at Whakapapa, and examine ash and lahar deposits in the Whangaehu River at
Tukino. Results of these investigations are not available at time of this
report.  A helicopter-lifted party sampled recent ash deposits on the
upper slopes of Ruapehu.  They encountered a ground-hugging plume of SO2
gas being blown down the upper slopes at Whakapapa.  This experience
demonstrated the possible existence of a gas hazard at Ruapehu during
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.

IA Nairn  for 
Dr CJN Wilson, Programme Leader, Volcanology