May 26 2003, 11:30 am - Ruapehu Volcano

Since the middle of March 2003 the temperature of Ruapehu's summit Crater Lake has been slowly rising, and is now slightly over 40°C. Similar temperatures were observed in January 2003 when the lake temperature reached 42°C.

This morning around 10.00 am a steam plume was observed above the Crater Lake, rising 200 - 300 m. No seismic activity accompanied this plume, suggesting there was no eruption and that the plume was generated by atmospheric conditions alone. Steam plumes were also observed on April 21.

Ruapehu Crater Lake has been visited three times recently to record the lake temperature and collect water samples. The lake temperature has risen from 30°C on March 5 to reach 41.6°C on May 15. During this time there has been an increase in the background levels of volcanic tremor and some volcanic earthquakes have also been recorded. There have been no significant changes observed in the lake water chemistry.

This is the fourth time that the temperature of the Crater Lake has risen above 35°C since the start of 2001. It is not unusual for the temperature of the Crater Lake to cycle over periods of 6-9 months. Minor hydrothermal activity can occur in the lake during the temperature peaks.

As there is no change in activity the Alert Level for Ruapehu remains at Alert Level 1.

Brad Scott
Volcano Surveillance Co-ordinator