Nov 9 1995, 4:00 pm - Ruapehu Volcano

Situation Summary

As of 16:00, the following information is available:

• Since about 10:00 today the seismic pattern has changed at Ruapehu. Volcanic tremor has been recorded by the Dome with an average ground velocity of about 2 micrometres per second. The small A-type volcano-tectonic earthquakes which characterised the records for the last few days have stopped, being replaced by high frequency eruption earthquake signatures, most recorded only on the Dome seismograph. These events most likely accompany small ash eruptions from the active summit craters. Unfortunately weather conditions have prevented confirmation of the style of eruptive activity associated with the eruption earthquakes. Since 10:00 over 12 such events have been recorded.

• No GNS field parties have been active on the cone today.

• The COSPEC measurement made 7 November observed a SO₂ gas flux of about 5,000 tons per day (yet to be confirmed).

  Days since last major ashfall* on 14 October 1995	26
  SGV** at Dome: mean for 24 hours to 4:00 pm on 9 November 1995	<2 µm/s
  Days since SGV** last ≥10 µm/s on 27 October 1995	13
  SO2 flux: last measured on 7 November 1995	~5,000 t/day
  Deformation***: last measured on 7 November 1995	deflation
  * 1 mm thickness at 5 km radius ** Seismic ground velocity *** Tilt observed at Dome

Conclusions and Alert Status

Seismic activity indicative of explosive eruptions from the active vents has recommenced today. We advise the Alert Level remains at 3.

B.J. Scott (for C.J.N. Wilson)
Volcanology Programme Manager