Situation Summary

As at 22:30 the situation is as follows:

• Volcanic tremor continued at fluctuating but generally low levels during most of the 24 hours prior to 16:30 today. The tremor record from the Dome (summit) instrument was strongly banded into intervals of moderate and low tremor. Two small (M1 - M1.5) volcanic earthquakes were recorded at 04:34 and 06:34. A period of elevated tremor commenced at 15:50, and increased to intense levels by 16:30. This intense tremor has been accompanied by voluminous ash emission. Ash plumes have risen to more than 35,000 feet and a continuous ash cloud has been reported on the 20:00 weather satellite imagery, extending downwind at 30,000 feet to cross the coast between Napier and Waipukurau. Heavy ash falls have been reported between Waiouru and the east coast. The Desert Road has been closed by ashfall.
• Ash emission appears to have declined after about 20:30, accompanied by decreasing tremor levels. Tremor has been replaced by occurrence of numerous discrete volcanic earthquakes, the largest of magnitude about 3. At least one of these events (at 22:00) produced a loud boom heard by GNS staff collecting ash at the Wahianoa Aqueduct on the Desert Road. The volcanic earthquakes appear to record individual explosions in the summit crater.
• Bad weather has prevented ground observations of Ruapehu today.
• Observations of Ruapehu crater yesterday afternoon showed intermittent ash eruptions from the deep southern vent in the now dry crater basin, with mostly steam and gas emitted from the northern vent. This was the reverse of the situation observed during an overflight yesterday morning, when ash was being emitted from the northern vent, and steam/gas from the southern vent.

Alert Status

The present eruption episode at Ruapehu is continuing. From 16:30 to 20:30 today volcanic tremor was more intense than at any other time during this eruption sequence, accompanying voluminous ash emission. We advise that the Volcanic Alert Level remains at Level 3.

I.A. Nairn (for C.J.N. Wilson)
Volcanology Programme Manager