Jun 15 1998, 3:30 pm - Ruapehu Volcano

Since May 9 (see RUA-1998/01 and 1998/02) we have continued to record volcanic earthquakes and short periods of weakly enhanced volcanic tremor at Mt. Ruapehu. The Crater Lake changed colour over night May 11 - 12; however no other activity has been reported until today (June 15).

There has been no apparent volcanic response to the volcanic earthquakes or tremor until today, when observers about the volcano have reported steam plumes, the largest to about 500 m above the mountain. Mountain Air pilots have also reported that the Crater Lake is a very dark grey colour with a yellow sulphur slick in the central area. They also report a light coating of ash or mud is present immediately southeast of the crater, the area downwind of the crater lake.

No eruptions have been observed, but the steam plume observations and discoloured snow would suggest some small hydrothermal events are occurring through the crater lake.

Summary

A sequence of volcanic earthquakes and minor tremor level fluctuations continues to occur at Ruapehu. Except for a change in the colour of the Crater Lake overnight May 11 - 12 no activity has been reported from the crater until observations today of steam plumes and discoloured snow.

These data are insufficient to warrant a change in the alert level. The current changes are less than those which have preceded past eruptions.

We advise the Alert Level remains at Level 1.

Brad Scott
Volcano Surveillance Manager