Ruapehu - IGNS - Science Alert Bulletin V95/57

Friday 27 October 1995
1630 hours NZDT (UT +13)
Ruapehu Volcanic Activity

Situation Summary

As of 1630 hours, the following information is available.

*     At about 1900hr yesterday evening seismic activity at Ruapehu
increased again, similar to the increase yesterday.  The level of volcanic
tremor increased so that signals were again being recorded from the
Chateau and Ngauruhoe seismographs, and tended to over load on Dome.  This
increase in activity continued to 0600hr this morning.  Seismic activity
at  this time is at normal intra eruption levels (that is higher than
before this eruption sequence started, but low by comparison to some of
the highs we have seen during the eruption sequence).

*     Although the seismicity increased overnight there are no reports of
ash emissions, which is slightly anomalous (similar to yesterday). This
has to be related to how open the vent is and the viscosity of the magma
in the shallow part of the vent system However conditions for viewing have
been poor as a result of the volcanic fog (VOG) and low cloud about the
region.

*     Vigorous emission of a white-brown gas-rich plume (volcanic fog,
VOG) continues to occur from the summit crater of Ruapehu.  This plume has
been reported by various aircraft during the day, many reporting strong
odours. The plume appears as a brown colour (due to the high SO2 levels)
and many observers have mistaken this for ash enrichment.  The plume
continues to be ash poor.

Conclusions and Alert Status

The present eruption episode is continuing, with an increase in activity
over the last  24 hours, significant gas emissions and intermittent very
small ash eruptions.  We advise the Alert Level remains at 3.

BJ Scott for
Dr CJN Wilson, Programme Leader, Volcanology