Sep 2 1996, 11:30 am - Ruapehu Volcano

On Sunday evening a minor enhancement of eruptive activity, consistent with Level 2 (continued minor eruptive activity) occurred at Mt. Ruapehu. There were two short-lived periods of activity on Sunday evening. The latter activity caused minor ashfall over the Turoa Skifield area.

In summary, on Sunday evening between 17:44 and 19:00 there was an increase in seismic activity (indicative of ash eruptions) as recorded by the seismometers operated at Mt Ruapehu by GNS. This seismicity was accompanied by an ash eruption which was observed by aircraft and flight control services (Taupo). The eruption plume trailed down wind (east) about 50 nautical miles (90 - 100 km). No reports of ashfall have been received by GNS, but some minor falls should have occurred downwind of the volcano.

A second smaller seismic sequence occurred between 23:01 and 23:30 and this produced a minor ashfall on the Turoa side of Mt. Ruapehu. The ashfall was just significant enough to interfere with snow grooming activities. Observations early this morning suggest minor ash was associated with the plume.

Weak and intermittent low frequency volcanic tremor was recorded between 03:00 and 06:00 on Sunday morning, and may reflect processes that lead to the activity later in the day. Low frequency signals also accompanied the activity on Sunday evening.

There appears to have been some surprise expressed on some areas that eruptive activity has occurred at Level 2. Level 2 on the Scientific Alert Level is defined as 'continued minor eruptive activity' and the activity over the weekend is consistent with that definition, hence the alert level will remain at Level 2. Level 3 is defined as 'significant local eruption in progress', and the current activity is well short of that at this time. The Institute will continue to monitor the activity at Ruapehu and advise the responding agencies as the level of activity changes.

Further minor eruptive activity is expected from Ruapehu, and further larger events are a possibility.

B.J. Scott
Volcano Surveillance Manager