Oct 30 1997, 2:15 pm - Ruapehu Volcano

The ongoing minor eruptive activity from Crater Lake has now declined to levels that warrant lowering of the Alert Level for Ruapehu from 2 to 1. Volcanic tremor levels have been declining with time, but minor reactivations occur intermittently. Volcanic earthquakes have also been recorded and some of these have been accompanied by small eruptions. The last confirmed small eruption, which was accompanied by a volcanic earthquake, occurred at about 9.20 pm on Saturday the 18th. A COSPEC flight on Tuesday measured a SO₂ gas flux of 390 tons per day, which is typical for the current level of activity.

Presently the crater lake is confined to the southern half of the summit crater. It is a light grey colour, and its temperature is about 52 - 55°C. Small radial wave patterns are sometimes observed on the surface, indicating fluctuating water levels. No geysering or other disturbances have been recently observed in the lake.

The northern portion of the crater floor is now dry and a prominent fumarole field-vent system has developed in the northwest. The conspicuous steam plumes which have been frequently observed over the last week to ten days are derived from this area, as is the volcanic gas plume.

In summary, activity has decreased over the last week to ten days such that the Alert Level can be lowered, however an enhancement of the typical background activity remains. Further reactivation of activity could occur while the background levels remain slightly elevated.

The Alert Level is now at Level 1.

Brad Scott (for C.P. Wood)
Volcanology Section Leader