Dec 8 1995, 4:00 pm - Ruapehu Volcano

Situation Update

Activity at Ruapehu volcano has changed little since the last statement on November 29. While the volcano remains at Alert Level 2 we will only post irregular statements as are required.

The volcanic tremor has remained at a similar level to that observed for the last few days of November, with the mean seismic ground velocity about 3 - 4 μm/s. High frequency volcano-tectonic earthquakes continued to register on The Dome seismograph at the rate of 10 - 40 per day.

A visit was made to the active crater on Wednesday 6 December. During this visit there was only one lakelet present on the floor of the active crater, formed by the amalgamation of the two smaller lakelets previously observed. The eastern vent area was producing most of the volcanic plume (vog) and frequently appeared a yellow colour. Significantly less plume was originating from the western vent area (as observed from Dome). A water sample was obtained from the crater lake (57 °C), and a gas condensate sample was obtained from a high temperature fumarole (285 °C) to the north-west of the lake. Tilt-levelling surveys of the Dome and Knoll Ridge tilt sites show no changes.

Secondary lahars continue to occur. A moderate sized one has recently flowed down the Whakapapanui valley floor.

We advise the Alert Level remains at Level 2.

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